NEN 3650-1 chapters 8 and 9

Standardization Center

Replaces NEN 3650:1992; NEN 3650:1992/C:1996; NEN 3650-1:2001 Draft;

NTA 8000:2000; NEN 3652:1998, in part. Replaces NEN 3650:1992 together with

NEN 3650-2:2003 K1 inclusive

Netherlands Standards

NEN 3650-1 (nl)

Requirements for Pipeline Systems Part 1:

General

Section 2: Chapters 8-9ICS 23.040.10

July 2003

Netherlands Standardization Institute

Standards Commission 310 004 Transport Pipelines

Apart from exceptions provided by the law, nothing from this publication may be duplicated and/or published by means of photocopy, microfilm, storage in computer files or otherwise, which also applies to full or partial processing, without the written consent of the Netherlands Standardization Institute.Although the utmost care has been taken with this publication, errors and omissions cannot be entirely excluded. The Netherlands Standardization Institute and/or the members of the committees therefore accept no liability, not even for direct or indirect damage, occurring due to or in relation with the application of publications issued by the Netherlands Standardization Institute.

The Netherlands Standardization Institute will, with the exclusion of any other beneficiary, collect payments owed by third parties for duplication and/or act in and out of law, where this authority is not transferred or falls by right to the Reproduction Rights Foundation.

NEN 2003 Netherlands Standardization Institute

P.O. Box 5059, 2600 DB Delft

Telephone: (015) 2 690 390, Fax (015) 2690 190

NEN 3650-1:2003

Contents NEN 3650-1

Chapter 1 Subject and Area of Application Section 1

Chapter 2 Reference Standards Section 1

Chapter 3 Terms and Definitions Section 1

Chapter 4 Symbols Section 1

Chapter 5 Abbreviations Section 1

Chapter 6 Safety Section 1

Chapter 7 Process Safety Conditions Section 1

Chapter 8 Construction Design Section 2

Chapter 9 Type (land-based) Section 2

Chapter 10 Operation and Termination of Operations Section 3

Chapter 11 Offshore Pipeline Section 3

Appendix A (standard) Groups of pipeline systems Section 3

Appendix B (standard) Design aspects Design dataSection 3

Appendix C (standard) Design aspects Loading Section 4

Appendix D (standard) Design aspectsTension and deformation through loading Section 5

Appendix E (standard) Type with HDD-calculation Section 5

Appendix F (standard) Offshore pipeline aspects Section 6

Appendix G (standard) Trenchless Technology Section 6

Appendix H (Informational) Design aspects Pipeline land routes Section 6

Appendix I (Informational) Design aspects Field data Section 6

Appendix J (Informational) Pipeline Systems and European Machine Guidelines 98/37/EC Section 6

Appendix K (Informational) Sphere of Action Pressure Apparatus Section 6

Bibliography Section 6

Contents Section 2

Forward4

8.Constructional Design5

8.1 Pipeline Configuration5

8.1.1General5

8.1.2Route Definition5

8.1.3.Aspects Related to the Choice of Pipeline Alignment5

8.1.4Pipeline Depth Position6

8.1.5.Parallel Pipelines6

8.1.6Channel Containing Cables and Pipes6

8.1.7 Pipe Sleeve6

8.1.8Pigging Facilities7

8.1.9.Axially Rigid and Non-rigid Pipes7

8.1.9.1General7

8.1.9.2Axially Rigid Connection7

8.1.9.3Axially Non-rigid Connection8

8.1.9.4Compensator or Dismantling Joint Connection9

8.2Pipeline Design10

8.2.1General and Field of Application10

8.2.2Basic Requirements for Pipeline Design10

8.2.3Safety Level10

8.2.4Maximum Limit State and Serviceability Limit State11

8.2.5. Calculation Method11

8.2.6Limitation of the Survey13

8.2.7Loads14

8.2.7.1General14

8.2.7.2Load Type Further Information 15

8.2.8Load Combinations and Load Factors17

8.2.8.1Load Combinations and Load Factors for Maximum Limit States17

8.2.8.2Load Combinations and Load Factors for Serviceability Limit States18

8.2.9Verification Procedure and Material Factors18

8.2.10Pipeline Outline and Classification in Sections to be Calculated 19

8.2.10.1Outline19

8.2.10.2Sections to be Calculated19

8.2.11Mutual Influencing of Pipelines and Related Structures20

8.2.12Specific Design Aspects21

8.2.12.1Specific Design Aspects for Underground Sections21

8.2.12.2Specific Design Aspects for Aboveground Sections21

8.3Station Design22

8.3.1General22

8.3.2Requirements22

8.3.3Components23

8.2.4Connection Between Pipeline and Station24

9.Laying (on Land)24

9.1.General24

9.2.Distinction Based on Laying Method25

9.2.1General25

9.2.2Aboveground Pipelines25

9.2.3Open Excavations25

9.2.4Underground25

9.2.5Crossings25

9.2.6Trenchless technology25

9.2.7Landfall26

9.2.8Sinking26

9.3Laying Preparation26

9.4Transport and Storage27

9.5Laying Underground and Aboveground Pipelines27

9.5.1Tracing and Marking27

9.5.2Route Study27

9.5.3Site Layout27

9.5.4Activities Near High-Voltage Connections and /or Overhead Wires of Railways and Tramways28

9.5.5Underground Pipeline Groundwork28

9.5.5.1General28

9.5.5.2.Trenches28

9.5.5.3Storage of Excavated Ground28

9.5.5.4Use of Explosives29

9.5.6Pipeline Laying in Open Trenches29

9.5.6.1General29

9.5.6.2Dry Trench Laying29

9.5.6.3Wet Laying30

9.5.6.4Measuring off Pipelines30

9.5.7Trench Backfill30

9.5.7.1General30

9.5.7.2Pipeline Design Requirements and Ground Characteristic Changes30

9.5.7.3Requirements Related to Grade Use31

9.5.7.4Soil Deficits and Soil Surpluses32

9.5.7.5Warning Tape33

9.5.7.6Site Finish33

9.5.8Proximity and Crossing of Underground Structures (Including Existing

Cables and Pipelines)33

9.6Laying Crossings33

9.6.1General33

9.5.2Pipe Sleeve33

9.6.3Trenchless34

9.6.4From the Building Pit Without Groundwater Extraction34

9.7Station Construction34

9.8Cleaning and Out-of-roundness Check34

9.8.1General34

9.8.2Cleaning35

9.8.3Out-of-roundness Check35

9.8.4Drying35

9.9Tests35

9.9.1General35

9.9.2Test Plan36

9.9.3Completion36

9.9.4Safety During Testing36

9.10Delivery37

9.10.1Documents37

9.10.2Precommissioning and Commissioning37

9.11Verification and Inspection37

9.12Safety38

9.12.1General38

9.12.2Compliance with Safety Regulations38

9.12.3Construction, Environmental and Safety Plan38

9.12.4Accessibility of Adjoining Buildings38

9.12.5Third Party Requirements38

9.13Environmental Contamination39

Foreword

This standard is a revision of NEN 3650:1992. Besides steel pipe which was the hallmark of the 1992 publication, this edition includes other pipeline materials.

The standard is divided into parts. The first part includes general requirements for pipeline systems. The parts that follow include requirements specific to the pipeline material dealt with in that section, NEN 3650-2:2003 Steel, Draft NEN 3650-3:2003 Synthetics, Draft NEN 3650-4:2003 Concrete, and Draft NEN 3650-5:2003 Cast Iron. The standards series has been drawn up under the aegis of the Netherlands Standards Commission 310004 Transport pipelines.

NEN 3650-1 has the status of a national standard. The section includes general guidelines from the earlier NEN 3650:1992 and NEN 3650:1998. Material-specific requirements are included in the relevant sections dealing with those materials. Additions are made to general regulations whenever the use of materials other than steel makes this necessary. Some standards have been withdrawn, as requirements have been adjusted from the standpoint of technological progress, namely, with respect to the total life-cycle approach to external security (risk-control during design, installment, maintenance and shut-down), design calculation and the relation to (European and international) standards and directives. New attention is now being paid to the choice of route, articulated pipelines, offshore pipelines and grooveless techniques. A probabilistic approach was applied to structural design, where assumptions are made about various loadings (internal and external) and properties of materials. Via a model calculation, the effects on the structure are determined, which must be compared with the minimal limit values and boundary conditions. Backgrounds of the new calculation methods are covered in a supplement to NPR 3659:1996/A1:2003.

Appendices A,B,C,D,E,F and G are the components of which this standard consists. Appendixes H,I,J and K are informational components of this standard.

Because the Figures in this standard are in large part adopted from the old standards, and the additions were made outside NEN, the standards and editing rules for technical drawings have not been completely followed which can be seen from the captions to the Figures. In the text part of the standard, however, correct standards were utilized.

Revision of Standard

NEN 3650-2 is divided into Sections. There is an annual review to determine whether or not the revision of one or more Sections is necessary. The content of each Section is examined minimally once every 5 years. Proposals for revision must be submitted in writing to NEN.

Purpose of the Standard

The purpose of the Standard-series is to obtain underground pipeline systems safe for people, the environment and property, by making requirements for the design, installation, start-up and shut-down of pipeline operations that will guarantee a durable, effective, and efficient system.

This demands safety regulations. Deviation from the (fixed) regulations of this standard is only possible, if it can be shown that the same or higher level of safety will be otherwise attained.

Interface EN- and ISO standards

Relative to the relevant EN standards for the pipeline-technical domain, this standard adds additional details for conditions in the Netherlands.

The stipulations of this standard, including the adopted revisions according to NEN-EN 1594:2000 and ISO 13623:2000, are applicable to pipelines, in that this is also in compliance with the stipulations of NEN-EN 1594:2000 and ISO 13623:2000.

Use of Standard

The people applying the standard, must be familiar with the materials employed and be in possession of the relevant expertise.

The designer, builder or user of the pipeline system is reminded that this standard is not a design specification nor a handbook.

8.Constructional Design

8.1 Pipeline Configuration

8.1.1General

The design, laying, operational management and temporary and/or final decommissioning of the pipeline(s) should be taken into consideration when selecting the route. Future urban and industrial developments near the route must be considered as well as ensuring that the number of adjustments, rerouting or limitations continue to be kept at a minimum in the future.

8.1.2Route Definition

The activities that must be performed before a route can be defined as definitive and before a pipeline can be laid are given step by step. H.1 contains extensive descriptions of the activities.

1) Provisional route determination;

2) Obtaining planning approval;

3) The detailed proposal for the route;

4) Obtaining the required licenses and permits, discretionary permits and approvals;

5) Obtaining the required real rights and private licenses;

6) Obtaining and arranging the required working strips for laying;

7) Paying and arranging, respectively, all compensations, damages, value appraisals, etc., including future damage and cultivations;

8) Recommendations and reports in relation to agriculture-technical data;

9) Collecting specific information and recommendations and implementation regulations for bids and the execution of the work.

8.1.3.Aspects Related to the Choice of Pipeline Alignment

The pipeline configuration must be designed in the chosen route strip in view of the risks involved and, where possible, these must be limited. The following must be taken into consideration as well as other issues:

present and future underground infrastructure works;

present underground obstacles and contamination (foundations that have not been removed, left behind piles, ditches filled with waste, land contamination, old landfill sites, tree stumps in boggy subsoils, asbestos cement in rubble hardening, war residues, etc.; see also 1.4);

local changes in the nature of the soil (creeks and streams grown over by stumps of vegetation, swamps and dunes);

accessibility of the pipeline during laying, management and removal;

expansion possibilities for internal pressure and temperature changes;

bends and corner radiuses in rigid or sectioned (tension-resistant or not) pipelines in connection with thrust effect and/or thermal expansion;

sand piles or vertical synthetic drains for HDDs or GFT drillings (at least 2.0 m clear space is recommended between the bottom of the pile or drain and the top drill passage);

connection flexibility in relation to constructions supported by piles in connection with settlement differences (dismantling joints, bellows, loops);

high-voltage cables and induction on steel pipelines or pipe sections.

8.1.4Pipeline Depth Position

The minimum required ground cover of 0.8 m should be increased in the following cases whereby ground cover must be applied that has been adjusted to the circumstances:

in areas where it may be expected that subsoiling, drainage or depth excavation will occur or where provisions have been made for a pipeline system in order to improve drainage;

at locations where ground excavations can be expected;

in areas that may be liable to erosion;

in situations where the pipeline may rise due to freezing;

at locations where waterways cross in connection with the risk that damages may occur due to ship anchors.

When the minimum ground cover of 0.8 m meets with important obstacles which makes it necessary to protect the pipeline against external mechanical damage, the pipeline must be protected by a covering construction.

The pipeline may have to meet certain requirements set by, among others, the owner of the ditch or the water manager when the pipeline crosses a ditch or watercourse. The ground cover of sag pipes may be increased with a supplement due to, for example, soil erosion and anchor risk as a consequence of navigation after consulting with the manager involved (see also NEN 3651:2003).

8.1.5.Parallel Pipelines

Between parallel underground pipelines a minimum of 0.4 m clearance must be maintained. This distance may be set at a larger value as a consequence of safety considerations (chain reaction when one of the pipelines fails).

COMMENT 1: The 0.4 m clearance size may be deviated from after mutual consultation between the parties involved. NEN-EN- 1594:200 specifies a clearance of 0.3 m. This is deemed to be too small in connection with accessibility for making connections, their inspection and management. Different criteria apply to drillings, sag pipes and crossings with water management projects.

COMMENT 2: It is advisable to allow the clearance between the pipelines to amount to at least 0.4 m and a practical minimum for the space next to the pipeline would be 0.5 m for pipelines for which the trench backfill will be compacted.

8.1.6Channel Containing Cables and Pipes

Pipelines in a channel containing cables and pipes must be configured in consultation with and according to the requirements of the manager of the channel containing cables and pipes. The channel is provided with the necessary engineering structures to safeguard a separation of interests with other land use (for example, water-retaining structures).

Pipelines in a channel containing cables and pipes have a smaller probability of failing than comparable pipelines in the field as a result of the undertaken measures and the degree of management and monitoring of the channel.

COMMENT: There is one pipeline channel in the Netherlands: Stichting buisleidingenstraat Zuidwest Nederland from Pernis towards Antwerp.

8.1.7.Pipe Sleeve

The use of pipe sleeves may be required in the following cases:

a)with horizontal directional drilling (HDD) crossings of pipelines as a result of which environmental contaminating substances (for example, hydrocarbons which are liquid as a result of atmospheric circumstances) are transported:

in groundwater protection areas;

in other areas should the Pleistocene be approached and/or be drilled up to less than 2 m. This also applies to Holocene sand embankments or swamps that have an open connection to the Pleistocene.

b)With horizontal directional drilling (HDD) crossings:

of liquid pipelines with storage basin dikes (see also NEN 3651:2003);

of pipelines as a result of which corrosive substances are transported before the pipeline material;

c)crossings with railways, see [23];

d)road crossing when pipe jacking of the pipeline itself is not possible;

The following requirements are made from the pipe sleeve (see also 9.6.2):

the pipe sleeve must be suitable to absorb all external loads and the external design pressure of the medium transporting pipeline in those cases in which this is specified in the design;

-the pipe sleeve must be put together in such a way that corrosion protection of the medium transporting pipeline can be safeguarded;

-the pipe sleeve must be flexibly sealed at both ends to limit to a minimum the groundwater circulation within the annular space and, thus, also the supply of oxygen.

8.1.8Pigging Facilities

It may have been determined from an operational system requirement viewpoint that transport pipelines must be piggable. Aspects that help determine the construction and use of pigging facilities are:

location and orientation of the receiving and launching stations;

temporary or permanent set-up, accessibility and hoisting provisions;

shutoff valves, bypass pipes and blow-off and drainage provisions;

minimum corner radiuses, maximum internal centerline variations, Tees with guiding strips;

intelligent pig equipment to be used;

pigging position signaling;

internal lining.

8.1.9.Axially Rigid and Non-rigid Pipes

8.1.9.1General

Pipes are built using interconnected pipe elements. The connection method determines the behavior of the pipeline concerning the axial rigidity, normal force and deformation.

A distinction is made between pipelines with axially rigid and non-rigid connections.

8.1.9.2Axially Rigid Connection

Axially rigid connections are connections where the pipe elements are connected to each other rigidly. A continuous rigid pipeline is created applying this connection whereby the separate pipe elements are not (or do not have to be) distinguished strength-technically. The connection must be able to resist the same or a larger load as the pipe element itself.

COMMENTThe following are examples of this type: straight joints (steel), flanged joints, screwed pipe connections, mirror welding or electrowelded-on sockets (PE, glued (PVC, GVK) or laminated (GVK) connections).

8.1.9.3Axially Non-rigid Connection

Articulated Pipeline

An articulated pipeline is made with non-rigid connections between separate pipe elements. The bending or torque moment that is transferred through the connection (negligible) is regarded as small. These pipelines are referred to as flexible pipelines as well as rigid connections.

COMMENT 1All types of bell-and-spigot joints can be viewed as examples of this type of connection. Bell-and-spigot joints are applied in virtually all pipeline materials: cement (pretensioned or not), thermoplatic and thermosetting synthetics, steel, fiber cement, ceramics and (nodular) iron.

Rubber Ring

Sealing against internal (and/or external) pressure is provided in most cases by a rubber ring that is placed in a bell-and-spigot joint. The cross-section of the ring can be circular or it can have been modeled to fit in the openings of the bell and/or spigot.

The rubber ring must be able to resist the design pressure(s), the deflection difference between bell and spigot end, see [13], and the chemical and microbiological internal and external environment of the pipeline system.

The sealing effect of the ring must be guaranteed in relation to the admissible angle of rotation and extension and, in the case of shear force, must be transferred via the coupling (for example, a transition supported by piles or not supported by piles).

COMMENT 2Ground settlements and pipeline subsidence often lead to leaks in pipelines with bell-and-spigot joints in Holocene soils of the (Western) Netherlands. The clever design of a bell-and-spigot joint with a rubber ring play a vital role in relation to the above as does the durability characteristics of the ring (at least for the contemplated technical life cycle of the pipeline).

COMMENT 3NEN-EN 618, parts 1 through to 4 [43] apply to water and sewerage system applications and NEN-EN 682 [44] applies to gas applications.

Tension-resistant Connection

For most pipe materials, tension-resistant connections can be installed to ensure that they can resist the tension caused by the transfer of the normal force (tension). A safety device is provided to prevent that the bell and spigot is pulled apart. The joint is, therefore, tension-resistant.

COMMENT 4The reason behind making joints and connections resistant to tension is usually related (next to a sag pipe structure) to the choice of absorption of thrusts through ground friction along the sides of an elbow or Tee. The joints and connections for all pipe materials can be made tension-resistant in this manner except for cement and ceramics connections. Cement pipes with a sheet steel core are made tension-resistant by welding the cores together.

COMMENT 5Tension-resistant connections and joints can also be executed in such a way that the force transfer only exerts influence after an admissible extension of the bell. This is important when axial flexibility is required as well as tensile strength.

Angle of Rotation

Pipeline flexibility is created through the possible angle of rotation of the connections and joints. Local horizontal or vertical settlement differences followed by the pipelines or elbows (with a large radius) can be formed in the configuration of the pipeline.

Extension

An articulated pipeline that has been constructed as not being resistant to tension can extend freely in the axial sense when the pipeline, for example, undergoes a lateral resistance over a certain length. The bell and spigot slide out of each other without building up an axial force.

8.1.9.4 Compensator or Dismantling Joint Connection

Applying compensators or dismantling joints may be a solution when expected (abrupt) settlement differences or temperature differences produce more lateral or axial displacement than is admissible for the connection structure of the pipe elements.

Bellow Compensators

Bellow compensators can be applied for different objectives. The axial compensator is connected to compensate for the extensions or contraction of a pipeline (for example, as a consequence of temperature changes). The tension-resistant compensator (constructed with a hinge over an axis or with a universal joint) is suitable for allowing angles of rotation between pipe elements.

It is not advisable to apply steel bellow compensators underground because:

the bellows undergoes direct and indirect (transferred via dismantling effect) soil and traffic load;

the bellows waves fill up with the surrounding soil which means that the flexibility of the bellows is reduced and the stress in the waves increase;

the waves can internally act as sand and silt traps with the same effect, for example, with raw and waste water pipelines;

the bellows high-grade steel may be sensitive to stress corrosion and hydrogen brittleness;

When applying tension-resistant steel bellow compensators to include large discontinuous installation subsidence differences in crossings (for example, sag pipe connections), it must be demonstrated that these drawbacks have been resolved.

Rubber bellows can be applied to pipelines with a slight internal pressure. The bellows must be provided with hinges (tension-resistant).

Dismantling Joint

Dismantling joints are usually constructed of construction steel and are provided with gland sleeve connections with steel bearing segment rings for the relief of the rubber-sealing element; see Figure 7.

Figure 7 Example of a tension-resistant dismantling joint with gland sleeve connections

The (specific) structural strength calculation of the dismantling joint must be performed in consultation with the supplier. The subsidence difference (discontinuous) that must be included amounts to:

z = L tan (where

zis the maximum displacement of the dismantling joint;

Lis the dismantling length;

(is the maximum angle of rotation (for the usual value of ( = 4, z = 0.07 x L is used).

Tie rods are installed with tension-resistant dismantling joints that have to be secured during mounting (for example, with a double nut). The tie rods are charged with a tensile force that equals the pressure times the surface of the pipe sectional plane as a result of internal pressure.

COMMENT 1This applies if there is a thrust effect near the dismantling joint (elbow or branch). If this is not the case, axial force transfer is not required and, therefore, the tie rods are, in principle, unnecessary.

If both sides of the dismantling joint move in parallel to each other, an s clearance is required in the tie rods before z occurs which equals:

s = L((1 tan2 (-1)(for ( = 4 z = 0.07 x L and s = 0.0024 x L)

COMMENT 2This clearance could be included in advance of the tie rods by keeping the space free between the safety device and the stop flange. It is, however, not necessary unless both the connecting sections are completely axially fixed (for example, both have been poured in concrete foundations).

The lengthening (tensile pretensioning) that can generate expansion as a result of internal pressure over the angle ( in the tie rods, is a smaller order of magnitude than the abovementioned clearance s, is, moreover, opposed as a result of the surrounding soil (thrust absorption) and can be ignored.

8.2Pipeline Design

8.2.1General and Field of Application

This paragraph deals with the general provisions for the strength-technical design of land pipelines (straight pipe, elbows, connections and branch pipes). A distinction is made between underground (buried or trenchless installations) pipelines and aboveground (usually only local supporting) pipelines.

Specific provisions for offshore pipelines are dealt with in chapter 11.

Landfall pipelines must be dealt with as would land pipelines. As well as the crossing with the water-retaining structure (specific land pipeline), there is an overlap with offshore pipelines for the section in the shallow water just before the coast. The laying method used for the section has an important role in the design of the pipelines. Knowledge of land and offshore pipelines must be combined for this issue.

8.2.2Basic Requirements for Pipeline Design

Pipelines must be designed and constructed in such a way that the probability of exceeding a limit state is acceptably low for the anticipated duration of use.

Measures must be taken when it is reasonable and possible to limit any potential damage to the pipeline by avoiding, undoing and/or reducing hazards that threaten the pipeline and/or it should be designed in such a way that the related hazards can be resisted appropriately (see also Table 2).

8.2.3Safety Level

The required safety level is determined by the consequences in case of pipeline failure. A more serious consequence demands a lower level of risk of failure. A pipeline that is designed, laid and managed based on the requirements of this standard complies with the required risk of failure level which is achieved through a combination of (a) external measures, (b) strength-technical design requirements and (c) installation requirements .

The contribution of the strength-technical design is further specified in 8.2, especially, the loads and load combinations to be taken into account, the load factors to be applied, the calculations to be performed, the strength functions to be used and the tests to be performed.

Differentiations in strength-technical pipeline design are achieved by the following among other elements:

the quality of the piping design. This not only refers to the strength and the deformation capacity but also the possibilities of achieving correct installation, avoiding potentially dangerous situations, building in resilience, making inspections possible during implementation and operation, etc.;

the size of the load factors to be applied and the load combinations to be assessed. The size is partly determined by the pipeline position (pipeline in the field, pipeline in crossings with important water management projects, area class in relation to, for example, natural gas transport);

the volume and quality of the calculations to be performed to determine the response of the piping under the expected loads;

the reliability of the strength functions based on which the results of the calculations must be tested;

the requirements for the pipeline materials to be applied (such as for steel: strength and toughness of the parent material and welds, admissible geometry deviations such as wall thickness differences, out-of-roundness, welding imperfections, etc.);

Refer to NEN 3650-2 and Draft NEN 3650-3,-4 and 5 for further details on the above where the load factors and load combinations which are to be taken into account are given per material, pipeline type and position.

8.2.4Maximum Limit State and Serviceability Limit State

A limit state is a state where the set performance requirements are no longer complied with according to ISO 2394:1998. A distinction is made between maximum limit states and serviceability limit states:

-maximum limit states are limit states in which the collapse or other forms of structure failure occur or the maximum strength is exceeded (for example, the tearing open of the piping and leakage of substances which cause unacceptable damage);

-serviceability limit states are limit states in which the set requirements are not complied with any longer in relation to the correct operation of the structure (for example, presenting too much out-of-roundness, the occurrence of annoying vibrations or noise, leakage of substances that do not cause unacceptable damages).

Limit states and related strength functions are included in the sections which refer to each type of used material.

8.2.5. Calculation Method

Calculation values for the loads (so-called calculation loads) are used for the calculation. These are obtained by multiplying the representative loads with the related load factors. Next, relevant load combinations are determined.

Calculation values for material characteristics are obtained by dividing the typical values for the characteristics by the corresponding material factors.

COMMENTWhen the load, settlement, strain limit and tensile strength quantities and such are mentioned in this standard, the calculation value for the quantity involved is referred to unless otherwise stated.

The effects of these load combinations on the construction are determined through calculations, such as section forces, deformations of the piping, stresses, strains and any varieties thereof. Finally, it must be shown that no limit state has been reached. The effects must be tested in relation to the relevant strength functions for this purpose. See also 8.2.8 and 8.2.9.

COMMENTThe strength functions may involve material characteristics but may also relate to a calculation formula that describes the course of a certain failure mechanism (for example, implosion or buckling).

The calculation includes the following detailed steps; see also the flow chart in Figure 8.

a)The collection of design data.

The design data required for the design and the calculation are dependent on the nature and dimensions of the pipeline system. These are further described in the paragraphs below, in Appendix B and, for the various materials, in NEN 3650-2 and Draft NEN 3650-3, -4 and 5.

b)Outline and classification into calculation sections.

The pipelines and their loads must be outlined and divided into sections which are then calculated. See 8.2.10.

c)A simplified calculation can be tested or utilized.

d)Under certain conditions it is admissible to utilize a simplified calculation whereby usually only the internal pressure is taken into account. Such a simplified calculation has been elaborated further in NEN 3650-2-2003.

e)Determining the load combinations, loads and related load factors that should be taken into account as well as determining the limit states to be tested. Every section of a pipeline system must be examined for the influences of the loads given in 8.2.7. Based on this, the loads and load combinations that are relevant to that section must be determined. The calculation loads are assumed for the calculation. Section 8.2.8 provides information on the load factors to be applied.

f)The calculation of displacements, deformations, force and moment distribution and reactions.

This calculation depends on the uncoiled length of the pipeline configuration and, where it is required, the time relation. The trajectory and the size of the forces (normal force, shear force, bending moment, torque moment, ground loads and bearing reactions), the deformations (bending deformation and normal force deformation) and the (relative) displacements and deflections must be determined for the relevant combinations of loads. This applies to both the pipeline and also to the effects the pipeline has on its environment (soil and support, fixed point and conductivity structures, etc.).

g)Calculation of the quantities to be tested such as section forces, section capacities, stresses, strains and variations therein.

The positive and negative values of the stresses and strains that can occur in the wall of the pipeline system sections must be determined and, where necessary, also the course of the amplitudes and frequencies of stress and/or strain variations.

As a stress increase occurs in the pipeline elements as a consequence of geometry, it must be taken into consideration (for example, for elbows in rigid pipelines). Quantities that are not relevant or quantities in relation to which there is no doubt about the subordinated and/or favorably active character, do not have to be included in the calculations.

h)Determination of the limit values from the strength functions, taking material factors into consideration that relate to the relevant limit states. These are material-specific and are further described in the material section concerned.

i)Testing

The section forces, sectional deformations, stresses, strains and other values obtained through the calculation loads may not exceed the limit values.

Figure 8 Strength Calculation Flow Chart8.2.6Limitation of the Survey

The survey can be limited or be dropped for certain sections when:

-a simplified calculation is permitted (specified in Figure 8 to the right). This calculation, however, is material-dependent and applies under specific preconditions. See the relevant material section in this standard;

-there are results available from a previously performed survey of an identical or comparable pipeline system and the loads that apply to these results are also comparable and/or higher;

-there is no doubt about the subordinated and/or non-relevant or contrary (favorably working) character thereof in relation to certain loads.

8.2.7Loads

8.2.7.1General

Load means all physical processes that lead to deformations and/or stresses and/or displacements of the piping in the pipeline material.

An inventory of permanent and incidental loads that may operate on the pipeline system is required for the pipeline system design.

The survey should include both the laying phase and the operational phase.

COMMENTLoads that occur in the laying phase can have a permanent character and can, therefore, remain during the operational phase; for example, the application of pretension.

The size of every load should be checked for both phases. The loads thus obtained or the combinations thereof form the basis for the design of the pipeline with regard to strength, deformations and stability.

The following load types and/or reasons, respectively, must be considered in the design if applicable:

-pressure (internal and external);

-temperature;

-soil;

-traffic;

-its weight;

-connecting structures;

-vibrations;

-other laying loads;

-incidental external loads;

-meteorological loads;

-water and ice.

A short explanation is given in 8.2.7.2 regarding the load types. Refer to 11.4.2.3 for specific load types or reasons for the load for offshore pipelines.

Annex C offers methods that can be utilized to determine the size of the loads.

COMMENTThe typical load can be utilized as a representative value whereby a distinction can be made based on:

-variable loads; for which usually the used typical load is that which is expected to be reached no more than once during the life cycle;

-permanent loads; for which usually the average value is utilized as the typical load unless the load concerned shows a relatively high variation coefficient. The utilized load, in such cases, for which the probability of the value being exceeded is less than 5%.

8.2.7.2Load Type Further Information

Pressure

The pressures to be utilized in the survey are:

-the maximum and minimum negative pressure and excess pressure (maximum operational pressure, design pressure), respectively. The negative pressure has to be increased with any (hydrostatic) existing external excess pressure;

-pressure impulses in the media as a consequence of opening and closing the valves and/or starting or stopping the pumps, compressors and such (incidental pressure increase), cavitation after pipe burst;

-internal pressure during testing;

-pressure variations during business operation (in relation to limit state fatigue).

The determination method for the force of these loads is specified in C.2.

Temperature

All thermal loads (these are loads that occur as a result of a hampered and/or hindered thermal deformation of the pipeline) must be utilized in the survey.

COMMENTThermal deformation can occur due to temperature variations of both the media and the environment. Thermal load can occur as a result of uneven heating or cooling of the pipeline (for example, because of the sun or wind) or as a result of a layered movement of warm and cold media. In special cases: loads as a result of a considerable temperature gradient on the wall.

Heating as a result of sun radiation can lead to a significant pressure increase (for example, between two closed valves) in an aboveground closed section that has been filled with liquid.

The determination method for the force of the load due to temperature is described in C.3.

Ground Load

The following should be taken into account when designing pipeline systems:

-load due to directly and indirectly transferred ground loads (neutral ground load up to a maximum of the passive ground load);

-horizontal support pressure;

-load as a result of uneven vertical and/or horizontal displacement of the pipeline and/or uneven vertical and/or horizontal displacement of the subsoil;

-reaction forces of the soil as a result of loads on and shape-changing of the pipeline and displacement in relation to the surrounding soil (lateral vertical under and above, lateral horizontal, axial friction reaction and tangential friction reaction), respectively;

-load due to ground formations as a result of the vibratory extraction of sheetpile walls.

Ground loads that can occur when laying pipelines as a result of, for example, earth fill or one-sided ground load due to excavations must be utilized when designing the pipeline.

The designer must also take any load on the pipeline into account due to nearby foundations of hydraulic-engineering works, structures or buildings.

The determination method for the force of the ground load is described in C.4.

Traffic Load

The traffic load that occurs during the laying phase or operational phase must be included in the design.

The determination method for the force of the traffic load is described in C.5.

Load Due to Own Weight

The weight of the pipeline, sheathing and everything attached to the pipeline as well as the weight of the media to be transported or the test media must be utilized in the investigation (the appendages and other equipment belonging to the pipeline must be calculated as the pipeline's own weight).

Especially with aboveground pipelines the weight of snow or ice on the pipelines must be considered for the survey.

Underground pipelines may be forced up from under the groundwater level when in soft ground types (for example, peat or mild clay) or when the trench backfill liquefies. Ground anchors or reinforcements of the pipeline can be used to prevent the above.

The determination method for the force of these loads is described in C.6.

Loads Due to Connected Structures

Both the reactions that are exercised on the pipeline by the support points (spring-based or rigid) and by connected structures (tanks, barrels, pumps, bridges, safety valves, platforms) must be taken into account for the survey.

Special attention should be given to displacement or rotation of support points or connected structures.

Load Due to Vibrations

Vibrations as a result of the media (compressor or pump) or as a result of the environment (machines, but also wind, waves or currents) can create pipeline loads. This must be investigated during the design phase. The determination method for the force of the load due to vibrations is described in F.2.2.4. Refer also to Appendix J of NEN-EN 1594:2000.

Load Due to Transport and Storage

Bearing loads of pipes during transport and storage demand necessary attention; especially in relation to thin-walled pipes and their stacking height, clear span and bearing saddles or blocking.

Other Installation Loads

Different load situations can occur when the pipeline is laid which must be investigated, such as:

-bearing load during storage, transport and lowering of the pipeline;

-loads due to the elastic pipeline laying;

-load due to the pretensioning of the pipeline;

-loads in relation to thrust boring, drag sag pipes and horizontal directional drilling.

Incidental External Loads

External incidental loads are usually similar to an impulse load. Impulse loads are, for example, created by:

-loads due to excavation, pile driving, foundation and cone penetration works, drilling operations, subsoiling, mechanical draining, seismic surveys, etc. (see also Appendix K of NEN-EN 1594:2000);

-falling objects;

-anchor forces at waterway crossings;

-failure of nearby pipelines;

-mining activities and earthquakes (see also Appendix C and Appendix F, respectively, of NEN-EN 1594:2000);

-landslides or movements of ground deposits, etc., as a result of processing due to heavy rainfall.

Use can be made of data from available literature for determining incidental external loads. Generally, these loads are not involved in the normal strength calculation of the pipeline but the safety of the pipeline against these types of loads are investigated separately in a risk assessment and the pipeline is provided with additional risk limiting provisions if required.

8.2.8Load Combinations and Load Factors

8.2.8.1Load Combinations and Load Factors for Maximum Limit States

Pipelines and related parts, such as, fittings and supports or attachments, must be able to withstand unfavorable combinations of loads that may occur simultaneously with sufficient reliability, provided that:

-the extreme value of a changing load does not have to be combined with the extreme values of other changing loads or with special loads;

-a special load does not have to be combined with extreme values of changing loads or with other special loads.

The Q load combination to be considered can, in general, be formulated as follows:

(

Q = (g x Grep + (qi x Q1irep +((qi x (t x Qirep

1(2

where:

(gis the load factor for the permanent load;

Grepis the representative value for the permanent load such as the equilibrium of the pipeline and the weight of the ground cover;

(q1is the load factor of the contemplated extreme changing load;

(is the reduction factor dependent on the anticipated duration of use (often it is taken to be 1);

Q1repis the representative value for the contemplated extreme changing load;

(qiis the load factor for the i load;

Qirepis the representative value for the i load.

By constantly taking a different load extreme, all load combinations can be determined that can occur with a certain degree of certainty.

The effects of every load combination must be determined on the pipeline (forces, deformations, stresses, strains, etc.) and it must be shown that no extreme limit state is being exceeded.

Load combinations and related load factors to be taken into account are partly material-dependent. This is due to the fact that some of the contemplated limit states and calculation models to be applied are material-dependent. Refer to the material-dependent section in connection to this to obtain further elaboration of the load combinations and load factors to be taken into account.

A number of geotechnical characteristics play a role in relation to ground loads. The calculation values of these geotechnical parameters must be determined when determining the ground load calculation value. Next, the load should be determined via a calculation model to which a model factor (as load factor) is applied. Refer to B.4.2 for more information.

It is not always clear from the start whether a certain geotechnical size will contribute positively or negatively towards the contemplated limit state. Both options must be contemplated in that case.

8.2.8.2Load Combinations and Load Factors for Serviceability Limit States

The same formulation can be utilized for the verification of the serviceability limit states for the load combinations to be taken into account as utilized with the extreme limit states with the provision that lower load factors are taken into account (usually (q = (qi = 1.0) and the number of load combinations is lower. Material influence is also active here and we again refer to the material-dependent sections.

8.2.9Verification Procedure and Material Factors

For every load combination, the effect of the load combination on the structure has to be tested for all relevant mechanisms in relation to the calculation value of a corresponding strength size. The calculation value for the strength has to be larger than or at least equal to the load effect in all those cases:

Rd ( Sd

where

Sdis the calculation value for the load effect for the effective load combination;

Rdis the calculation value for the strength of the effective mechanism.

The following general formula applies for determining the calculation value for the strength:

1{Xk1Xk2}

Rd =-----R------- ,------ ,

(M(m1(m2

where

R{..}is the strength function;

Xkiis the typical value of a material characteristic;

(Mis the partial factor for the whole calculation model;

(miis the partial material factor related to an individual XI strength characteristic;Examples of material characteristics are yield stress or failure strain.

Refer to B.4 for the size of the factors concerning ground and refer to the material dependent sections in this standard for material specific factors.

COMMENT 1Often a value is taken, which may be below the limit by 5%, as typical value for strength functions or material characteristics. An average value or a safe average value may be involved with soil. The above is related to the nature of the mechanism and the quantity of data (see B.4).

COMMENT 2Geometric quantities (centerline, wall thickness) can also occur in a strength function. Usually the nominal value is used. Exceptions are geometric quantities with an important influence of the safety such us out-of-roundness.

COMMENT 3The uncertainties in the calculation model (of load based on load effect) are sometimes taken into account on the strength side and sometimes on the load side. It is absolutely crucial that these uncertainties are not forgotten.

Figure 9 specifies the quantities that are important when assessing structural safety.

Figure 9 Frequency distribution for load and strength

8.2.10Pipeline Outline and Classification in Sections to be Calculated

8.2.10.1Outline

The pipeline is outlined to obtain a system of beam elements for the pipeline and spring elements for the supports. The surrounding ground is also outlined to obtain a spring system for underground pipelines.

Loads, displacements and obstructions for the whole pipeline system must be considered as cohesive for both static and dynamic aspects. This means that also for the sectional survey, the connection and equilibrium conditions everywhere in the pipeline system should be sufficiently met.

It also means that points for which the following is known must be limited in relation to the contemplated section of pipeline:

-displacements (translations and rotations);

-forces or moments; or

-the connection between the displacements, on the one hand, and the forces and moments, on the other hand.

8.2.10.2Sections to be Calculated

The sections to be calculated are, among others, the following:

1)underneath ground level with special attention to:

-elbows (especially in connection to higher operational pressures and temperatures) and buckling;

-Tees;

-settlement sensitive areas;

-sections that have been pile driven;

2)connections on locations with special attention to:

-underground elbows at the end of long straight sections (thermal and pressure expansion);

-the transition of an excavated trench to a rigid support structure aboveground or not (for example, footings of pipeline bridges). It is advisable to include the underground and aboveground sections in one calculation model;

-with installation connections: attention for the often occurring wall thickness differences;

3)civil engineering infrastructure crossings:

-roads;

-railways;

-watercourses;

-storage basin water and dikes;

-primary, secondary and other water-retaining structures;

4)transition to implementation method:

-which is responsible for a settlement and/or subsidence difference (for example, a section that has been placed in a trench that connects to a thrust bored or drilled section).

Also when applying pipe sleeves, special attention should be given to subsidence differences;

5)abrupt transitions in soil conditions;

6)pipe sleeve transition of the position within a pipe sleeve to the section laid in the trench. Also the sleeve pipe should be checked for strength.

8.2.11Mutual Influencing of Pipelines and Related Structures

The survey to determine the effects of the loads is directed toward the structures that play a substantial role in relation to the operation and/or maintenance of the pipeline system as well as toward the medium transporting pipeline.

Anchor blocks, pipe sleeves, supports and connected structures (for example, pipeline connections to stations; see also 8.3.4) and such are involved.

Supports

The locations and design of the supports should be such that forces can be equally distributed and passed between the supports and pipeline to ensure that high local stresses in the pipe wall are avoided.

Due to subsidence differences, a large bearing reaction may occur at the location of the support(s). The bearing angle must be at least 60 to avoid peak stresses that have a pierced effect as a consequence.

Supports must be designed with at least the same safety level as the pipeline itself.

COMMENTIn special cases, it may be advisable to limit the maximum bearing potential of the support to avoid a too high bearing pipe reaction (for example, when subsidence occurs) and/or to make a transversal movement possible.

Local stresses in the pipeline that are due to the supports, such as bending and movement stresses in the wall, must be determined.

The influence of the rigidity and/or deformation capacity of the support including its foundation on the static and dynamic behavior of the pipeline system must be investigated by taking the force transfer relation of the foundation into consideration.

Connection of equipment and structures

Forces, moments, forced deformations from transfers and distortions arising from the presence of connected equipment must be included in the pipeline stress analysis.

Non-Supported Sections

Should non-supported sections (for example, clear spans) occur during the laying, burying or during the operational phase, the stresses that arise must be determined.

The maximum admissible span must be specified in the calculations. Dynamic aspects of the clear span must also be taken into consideration.

The actual span that is present must, in practice, be checked.

COMMENTUnchecked clear spans virtually do not occur in land pipelines; the phenomenon occurs more often in offshore pipelines due to sand transport over the sea bottom.

8.2.12Specific Design Aspects

8.2.12.1Specific Design Aspects for Underground Sections

Required geotechnical data:

-often occurring geotechnical values can be assumed for underneath ground level (see table C.3) in combination with or without a limited site investigation;

-the values have to be determined based on the ground investigation and must include advise from an expert geomechanical consultant (see also 1.3) in relation to special structures and/or strongly changing ground conditions or where settling of some importance are expected.

Load types:

-check pipelines in groundwater in relation to being set afloat during both the implementation and operational phase.

Construction settlements:

-the difference in construction settlements as a consequence of ground agitation and buckling or difference in implementation method or as a consequence of the vibratory extraction of a sheetpile wall should be taken into consideration as well as settling differences due to consolidation;

-a construction settlement difference of fv due to ground agitation, gradually (for example, sinusoidal) going from 0 to fv over a length L and back again should be used for pipelines laid in open excavations and with a careful trench backfill. The area encompassing the settlement difference, therefore, has a length that equals twice L. See C.4.7.2 for the determination of L.

Should no further survey take place on site in relation to the construction settlements, use must be made of the values of fv as specified in the tables in Appendix C;

-should certain minimum requirements be demanded from the implementation method to limit settling and settlement differences, they must be mentioned in the geotechnical report and must be respected during implementation.

8.2.12.2Specific Design Aspects for Aboveground Sections

Load types:

-own weight including media and liquid load, respectively, for hydrostatic testing;

-any condensate and/or liquid propylene in gas pipelines;

-wind load (only if the centerline and the height position trigger this off);

-snow and glaze in relation to cold media (< 0 C) and/or thermally insulated pipelines.8.3Station Design

8.3.1General

Rules are given in this paragraph that should be observed when designing and operating stations.

Gas pressure control and measurement stations must comply with NEN-EN 12186:2000 and NEN 1059:1994 and Draft NEN 1059 1059-2000. Compressor stations must comply with NEN-EN 12583:2000. The strength-technical design of the stations falls under this standard.

COMMENTParts may be present in stations (pressure equipment and pipelines with a pressure > 0.05 MPA) which fall under the Pressure Equipment Directive (PED); [34]. The PED has been implemented in the Netherlands in the Pressure Equipment Decrees; see Appendix K. Pipelines do not fall under the scope of application of the Decrees.

8.3.2Requirements

General Requirements

The requirements that must be met by the station layout depend on the environment, climatological conditions, the station type and the substance to be transported.

Every station must be designed in such a way that:

-the nuisance and danger for the environment are limited to a minimum;

-the station (or parts thereof) can be simply decommissioned by using a few valves;

-all parts have easy access for operation, inspection and maintenance purposes;

-the correct operation is assured for a long period under all circumstances that can occur on location;

-there will not be any detrimental consequences of settlement and subsidence differences between pipeline and station, corrosion or other reasons;

-unauthorized operation, vandalism and sabotage are avoided and/or hampered considerably.

Measures must be taken for arrangements in an unheated space as well as in the open air sheltered or not sheltered by a side shelter or a few walls that will prevent disturbance of the correct operation due to weather influences.

COMMENTThese measures can be, among other measures, the following:

-providing a freeze protection cable to ensure certain parts are not frozen (for example, controllers);

-special measures against corrosion, among others, sealing the space between flanges;

-measures against seepage, for example, via a ventilation opening towards a membrane chamber of a regulator, safety, electronic and instrumental equipment, etc.

Distances

Stations must be positioned in such a way that hindrance and danger to the environment is avoided as much as possible. The distances used between stations, on the one hand, and buildings, roads, railways, high-voltage lines, etc., on the other hand, have to meet certain requirements.

When choosing the distances between stations and the underlying distances of equipment and devices in the station, safety, maintenance and operational management must be taken into account.

COMMENT 2NEN-1059:1994 and Draft NEN 1059:2002 include safety distances for gas pressure control and measurement stations. The distances contained in these standards apply as minimum safety distances for objects where people can be found; the distances in relation to roads, railways, watercourses, other ignition sources and boundary partitions are also relevant. The size is determined by the station being continued.

Fencing

A station should be surrounded by fencing, should circumstances demand this, that is installed in such a way that access by unauthorized persons is prevented if possible and which should be provided with a clearly visible warning and prohibition sign; see NEN 3011:1986.

To ensure that people can escape from the area immediately next to the station in case of an emergency, there should be sufficient access points (one or more, depending on the requirements of the local authorities) in the fencing. This also applies in the case when a station has been housed in a building.

The access points must open towards the outside and you should be able to open these from the inside without a key. Other provisions can also be made that offer the same escape possibilities. If the size of the station justifies it, accesses must have been measured and implemented in such a way that accessibility for fire-fighting equipment and ambulances is safeguarded.

Electric Installation

The electric installation in stations must comply with the requirements set down in NEN 1010:2000, NEN 1041:1982 and NEN-EN-IEC 60079 for as far as these are applicable. The electric lighting must be implemented in such a way that exits and critical places around and in the station are clearly visible during the night and when there is fog.

Lightning

Provisions must be made against lightning where this is required based on NEN 1041:1982 (for example, when explosion hazards are present at the installations). The provisions must comply with the requirements contained in NEN 1024:1992.

Electrostatic Loads

Liquids can generate electrostatic loads, when flowing along the wall of a pipeline, that can ignite an explosive mixture. Pipelines, pipe sleeves and devices that can have an electrostatic load must be grounded or must be conductively connected.

The resistance between the pipeline and ground must amount to more than 6 ohms to offer protection against electrostatic loads.

8.3.3Components

General

All separate components of stations must comply with their functional requirements.

Mechanical devices (such as compressors and pumps), electrotechnical devices (generators, batteries), components connected to pipework (pipes, ancillary equipment, flanges, bolts, gaskets, valves) are examples of the above.

The total installation must, moreover, comply with the requirements related to reliability in operation, safety and dependability. Safety in relation to the environment and hindrance of third parties must also be at an acceptably high or low, respectively, level.

Protections

Aspects, such as the ones given below, must be given attention in relation to the above:

-explosion hazard (corrosion and leak detection, ventilation, hot surfaces, pressure protection);

-fire hazard (heat insulation, fire-extinguishing equipment);

-noise insulation (sound-dampening provisions).

Auxiliary Lines, Etc.

Devices within stations are often linked to each other using internal piping. Piping for oil, gas, steam, compressed air, water, chemicals (for example, inhibitors) as well as measurement, control, auxiliary gas and sampling pipelines are examples. This piping and related valves, flanges, adaptors, elbows, etc., must be manufactured from adequate material and must be suitable for the operational pressure and temperature of the connected devices. Pipelines in stations must be designed based on this standard as far as it is applicable. Requirements that should be met by flanges, gaskets, bolts, nuts, valves and other fittings are given in the material sections concerned in this standard.

8.3.4Connection Between Pipeline and Station

Mutual influencing must be taken into account when designing the connections between the sections and the stations (see also 8.2.7).

Special attention must be given to the following regarding connections of the aboveground components with the underground pipelines:

-displacement differences due to thermal expansion of the pipelines;

-subsidence of the subsoil as a consequence of pipeline laying and settling or swelling as a consequence of grade changes;

-vibrations in components and aboveground sections due to machines (for example, compressor throbbing or flow induced throbbing);

-expansion and shrinking of the pipeline as a consequence of temperature fluctuations and pressure changes. If required, the pipeline must be anchored or must be implemented flexibly to ensure that temperature or pressure fluctuations do not lead to unacceptable stresses in components, supports or foundations.

COMMENTThe (welded or flanged) valve that forms the separation between the station and the pipeline, can be positioned on a transition in foundation method (uneven subsidence). It is advisable to investigate whether the valve (and any flanges) can withstand this.

9.Laying (on Land)

9.1.General

The laying of the pipeline system must be performed as described and specified in the approved specifications and approved drawings from the design phase. The methods, the organization chart and the work procedures for the installation and delivery must also be specified in the descriptions. The documents must be available before the installation phase is started.

The requirements and provisions for the protection of health and safety of the public, involved personnel and the environment must be specified in a safety, health and environmental plan. The requirements stipulated in the relevant legislation and regulations, standards and licenses and the identification of potential risks and hazards including the corresponding measures and emergency procedures must be described in the plan.

Competent supervisory personnel must supervise the implementation of the work. The persons carrying out the work must have all required qualifications for implementing the work.

Hindrance of the owner and/or users of the involved lots and damage to goods or crops must be limited as much as possible.

COMMENTIt is advisable to identify beforehand the objects that could be influenced by the construction of the pipeline system. Objects can affect, for example, existing roads, railways, watercourses, footpaths, cables, pipelines and buildings.

It is advisable to name the temporary provisions and safety provisions required to protect the objects during construction and to harmonize these with the involved owners, managers and authorities when defining temporary provisions.

When large (implementation) installations are expected, it is recommended that marginal properties which are influenced by the laying are subjected to a zero value investigation (determination of the situation on the contract date).

9.2Distinction Based on Laying Method

9.2.1General

A distinction can be made between aboveground and underground pipelines in relation to laying land pipelines. An underground pipeline can be further subdivided into underneath ground level and crossings.

Refer to 11.5 for information regarding laying offshore pipelines. The landfalls of offshore pipelines are viewed as land pipelines in this standard.

9.2.2Aboveground Pipelines

Laying aboveground pipelines includes the assembly and installation of pipelines that are not continuously supported (in relation to the ground) but locally.

9.2.3Open Excavations

The pipeline is directly buried in a dry, excavated trench or the pipeline is buried and immersed in a trench filled with water.

9.2.4Underneath ground levelThe laying of an underground pipeline in the underneath ground level includes assembly and installation of a pipeline in an excavated and again filled trench. Trenchless technology can be used underneath ground level when this is attractive financially or for other reasons.

9.2.5Crossings

Crossings are installed depending on the circumstances:

a)in an open excavation;

b)using trenchless technology (drill and thrust boring techniques and HDD);

c)by spraying;

d)by sinking;

e)using jumpers and pipeline bridges.

9.2.6Trenchless technology

Drill and thrust boring techniques are subdivided into four main groups based on accepted terminology:

-Open Face Technique (OFT);

-Closed Face Technique (GFT);

-Pneumatic Drilling Technique (PBT);

-Horizontal Directional Drilling (HDD).

COMMENTDue to required uniformity in the method used for referring to trenchless technology, the abbreviations given above have become standard abbreviations in this sector.

Every drilling technique has its own specific application criteria and the choice of the most suitable method depends on:

-centerline, material and connections of the pipeline;

-nature of the object to be crossed;

-length of the crossing;

-ground conditions;

-groundwater level or groundwater potential.

The main groups are further specified in Appendix G.

9.2.7Landfall

The laying of a landfall can mean crossing a primary water-retaining structure (see also NEN 3651:2003). Special (temporary or permanent) structures are required to secure the stability of the coastline during laying or operation time.

In addition to the land pipeline aspects, the wave, current, storm surge, morphology and sand transport phenomena play a role for the landfall.

9.2.8Sinking

The pipeline is installed in a watercourse to be crossed when sinking. First a trench is dredged on the bottom.

Installing a prefabricated pipeline or sag pipe can be achieved by dragging with a winch or hoisting with cranes or hoisting sheers or driving, filling and immersing or using combinations of the aforementioned methods.

The dredged trench must be backfilled with care after the sag pipe has been laid.

9.3Laying Preparation

The approved calculations, the drawings, the specifications, the geotechnical report, the construction descriptions, the safety, health and environmental plan and the identification of objects and facilities that are influenced by the construction must be available before the start and licenses must be available or you must be able to obtain them.

When a pipeline is being laid through cultivated land (arable land and meadows), a cultivation-technical investigation (see I.1) must be performed during the design phase. The cultivation-technical requirements and recommendations must be adhered to when the pipeline is laid.

If groundwater extraction is required during the laying, a geohydrologic investigation (see I.2) must be performed during the design phase. This must be done in relation to the extraction of groundwater and drainage thereof. The geohydrologic report must contain data related to the water quantity, water quality, environmental aspects related to this, the drainage type to be applied, period, discharge of drainage water and artificial recharge. Possible displacement of bottom contamination elsewhere should be kept in mind. During the installation and thereafter, the discharge must be registered.

Before starting with the laying, licenses must be obtained and private agreements with land owners and users must be concluded.

Arrangements must be made with third parties involved in relation to the site, the access to the site for personnel and material and/or the use of storage areas for material, machinery and equipment.

All interested parties (private persons, authorities and other managers) in relation to the installation must be warned and informed regarding the nature, the size and the duration of the activities before the activities start.

Owners of existing cables and pipelines in the route must be informed regarding the activities being contemplated. It is advisable to make a KLIC (Kabels- en Leidingen Informatie Centrum; Cable and Pipeline Information Center) notification well in advance of the start.

COMMENTDepending on the nature and size of the activities, the decision may be taken to hold a commencement discussion at which the involved pipeline managers and/or their representatives, license and/or permission holders and licensing authorities are present. The contractor presents, during this meeting, a plan of approach (working plan, planning, protective provisions, approved drawings and such). The customer will also provide in writing the name, address, and telephone and fax number of the contact that he has appointed for the duration of the works.

9.4Transport and Storage

Loading and unloading, transport and storage of pipes, fittings and other material must be kept meticulously separate to avoid damaging pipes, pipe ends, linings and other material.

Materials must be inspected to check for damage, deformations and deterioration. Materials with unacceptable damage, deformations or deterioration must not be installed.

COMMENTAspects that are important: pipe must be blocked to ensure that the lining is not damaged, do not roll or drag pipe, a stable storage, sufficiently wide hoisting belts made of a soft material, hooks must have a synthetic layer, the bottom of the pipes should not touch the ground when stored, adequate (temporary) protection against material degradation such as corrosion or UV and O3 effect, completeness of inspection certificates and other cover documents. In relation to transport and storage activities, the prevailing safety regulations (as supplied by the ARBO-wet, Working Conditions Act, and the Wet Gevaarlijke Werktuigen, Hazardous Plant and Equipment Act) must be observed.

9.5Laying Underground and Aboveground Pipelines

9.5.1Tracing and Marking

The center of the pipeline is traced. The pipeline route and the working strip as well as the special objects within the influence sphere thereof are marked whereby the location, type, depth and characteristics of the structure concerned are specified. The markings must be adhered to and/or detected during laying.

9.5.2Route Study

Before starting with the installation of the site and the building, a detailed route study must be performed. Inspection reports must be drafted in consultation with the parties involved.

9.5.3Site Layout

A working strip with sufficient width must be laid out for good and safe implementation of the activities and supply of material, machines and equipment.

Aspects that must be observed during construction and, later, restoring the working strip are:

-tracing, marking and placing warning signs near aboveground high-voltage lines under which the working strip can be found (in compliance with Chapter 10 of NPR 2760:1991);

-strength of the subsoil;

-access in relation to, for example, cattle;

-original function of the ground (for example, arable land, grassland, protected natural area, industrial area) and restoration of this function after pipeline laying (see the agriculture-technical report);

-felling trees with a permit or removing obstacles;

-any need to remove and separately store the topsoil (restoration of the original state, see the agriculture-technical report);

-sand embankment (quality and processing);

-source and discharge point;

-drainage;

-collected drainage (temporary);

-demolition of structures.

9.5.4Activities Near High-Voltage Connections and /or Overhead Wires of Railways and Tramways

Prior consultation must take place with the company under whose management the pipeline (or installation) falls in relation to the safety provisions to be made when work is performed near aboveground high-voltage cabling (also overhead wires of railways and tramways) and transmitter towers.

The safety provisions for high-voltage connections to be observed are included in chapter 10 of NPR 2760:1991.

9.5.5Underground Pipeline Groundwork

9.5.5.1General

Excavation work must be performed in such a way that damage to the cables and pipelines present in the ground is avoided. When excavation work is performed in parallel to existing cables and pipes, excavation must, by preference, take place within a distance of 1 m using shovels unless measures have been taken to avoid damage. This also applies for crossing cables and pipelines. Damage to the present (deep) drainage systems or irrigation systems must be avoided or adequately be repaired after laying. It must be avoided that the trench can be used for water discharge when non-horizontal trenches are used.

9.5.5.2.Trenches

The pipeline must be laid, according to the working drawings, with sufficient ground cover. It is important that excavation is not deeper than the level that is specified for the bottom of the pipeline in connection with occurring buckling of agitated ground. The slope must be adjusted to the trench depth, the drainage and the soil type to ensure the trench walls cannot collapse and/or subside. If required, the trench wall must be shored up using partitions.

COMMENTThe relevant safety regulations for slopes must be observed.

It is important to implement the trench bottom in such a way that the pipeline is laid as anticipated in the calculation. It may be necessary to lay a sand layer under the pipeline. To excavate deeper than required must be avoided in connection with occurring buckling of the agitated ground. Additional settling may occur as a consequence in soft subsoils.

The trench wall border must match the excavation depth, drainage and soil type.

The trench must be kept free of objects that may damage the pipe or lining of the pipe. Gravel, stones and/or other hard material near the final location for the pipeline must be removed. If this is not possible, the pipe must be provided with a protective lining or the pipeline must be embedded in clean (sandy) soil.

9.5.5.3Storage of Excavated Ground

Excavated ground must be stored in such a way that the original constitution of the ground profile is re-obtained as much as possible when the trench is later backfilled.

Topsoil present must be stored separately from the underlying layers as specified in the agriculture-technical report or in consultation with the manager of the ground. In certain cases, it may also be necessary to excavate and store the subsoil separately. The storage must be harmonized in relation to the local grade.

In principle, ground deposits are not planned above an existing underground pipeline. If this is necessary, however, it must be checked, in consultation with the pipeline owner, whether this is possible and whether special provisions must be made to protect the pipeline.

9.5.5.4Use of Explosives

If explosives are to be used, it must be provided for in the design of the pipeline. Special regulations apply and an explosion plan must be drafted.

COMMENTThe use of explosives for laying a pipeline will virtually never occur in the Netherlands with its relatively soft granular and peaty ground structure. It may even be impossible due to the buildings present. Special attention must also be given to any occurrence of liquefaction of sandy soils that are sensitive to this phenomenon.

9.5.6Pipeline Laying in Open Trenches

9.5.6.1General

A distinction can be made between laying an axially rigid and an articulated pipeline in a dry trench or in a wet trench.

9.5.6.2Dry Trench Laying

Axially Rigid Pipeline

The pipeline is lowered between the pipe elements in the trench after mounting the string and finishing the connections. The trench must be dry at this moment and must remain dry until the trench is backfilled. The pipeline must be laid in a dry bed.

COMMENT 1The laid pipeline can be set afloat should there be water in the trench.

The string must be lowered using hoisting equipment. The hoisting resources to be used such as hoisting belts and slings must be covered to ensure that the pipe and lining are not damaged.

It is important that as little as possible stress is allowed to build up in the pipeline both during composition and when lowering the pipeline. The admissible curvature of the pipeline and the slight rigidity of the elbows should be taken into account. The lowering must also be done without shocks to avoid buckling and wrinkling of the pipeline or other permanent deformations. After lowering the pipeline, the position should be corrected if required. The pipeline must thereafter be measured off. The use of resources not anticipated in the design to keep the pipeline in its place is not permitted.

Articulated Pipeline

Pile elements that are connected with a bell-and-spigot joint form an articulated pipeline which is not axially rigid. Articulated pipelines are, in general, built up in the trench. The trench must be dry during laying up to backfilling.

A rubber ring provides the sealing of the pipe connection for the internal pressure. You can check the correct assembly of the rubber ring during laying. This often leads to the decision to backfill the trench immediately after laying the pipe elements. Buoyancy forces on the empty pipe in the return groundwater must be taken into account. The trench backfill also prevents the articulated pipeline from becoming deformed through initial thrust during the hydrostatic test.

The available length by which it can be extended must be divided among the implementation phase and the final phase with connections that are not resistant to tension. Any direction corrections and the method for backfilling must be geared towards the available length by which it can be extended. During installation, the joint displacement that is available for the installation, whether internal or external, must be monitored.

COMMENT 2It is advisable to include the jointing openings of every connection when articulated pipelines to which access can be gained are involved. The opening is measured at 3:00, 6:00, 9:00 ad 12:00 oclock. The angle of rotation of the joint and the axial width of the joint can be determined from the measurements as well as the three-dimensional position of the pipeline. Requirements can be included in the design regarding the admissible rotation and width.

COMMENT 3It has been observed based on joint measurements that some pipe elements undergo a slight axial movement when pipelines are immediately backfilled after laying in soft Holocene ground. The impression exists that the elements only lay still after the groundwater level is stable.

9.5.6.3Wet Laying

A wet installation is appropriate when the area has relatively many watercourses or when the grade is so bad that many provisions are required to be able to achieve a dry trench and/or when this is impossible.

The trench is oversized in order to make a channel through which a section can be driven in or buried and, subsequently, sunk.

The laying method can be applied for both rigid and articulated pipelines. The connections in the articulated pipeline must, in that case, be resistant to tension.

9.5.6.4Measuring off Pipelines

In general, it applies that the location of the pipeline must be measured off in the open trench during laying. Preferably in coordinates (Rijksdriehoekscordinatensysteem!; national triangulation coordinate system). The measuring work must be updated accurately in digital or analog form. The measurement data are the basis for the as-built drawing of the pipeline.

9.5.7Trench Backfill

9.5.7.1General

The backfill work and site finishing must take place based on the agriculture-technical report and the safety regulations to be observed. The backfill of the ground in layers must take place after lowering the pipeline.

If installed wet, backfill must take place, by preference, in the water when the flow is directed downwards to ensure good compaction. The water has to also be driven forwards when backfilling to avoid water closing off in the trench to be backfilled.

In peaty areas, lightweight material is applied under the groundwater level (peat and wood fiber pellets) and Flugsand (i.e. volcanic tuff sand) or another lightweight granular material on top to limit settling.

The excavated material must be added with care in the correct sequence and should be free of stones and such to restore as much as possible the original profile. The trench must be filled with soil free of coarse and hard components up to a height of 0.3 m above the top of the pipeline to protect the pipeline and lining. This first backfill layer must have such a quality and must be provided in such a way that the pipeline is given an even and sturdy support on all sides and over the whole length. Backfilling must occur in such a way that the ground mechanical departure points, used in the design, are achieved.

A slight surplus height on top of the trench must be implemented, if necessary, with a view to consolidating the ground.

This must be done in such a way at road locations that the traffic will not be greatly disrupted or is otherwise warned using temporary traffic measures in consultation with the road manager.

9.5.7.2Pipeline Design Requirements and Ground Characteristic Changes

Softening

If the coefficient of soil reaction is too large to make safe positioning of the pipeline demonstrable, increasing the freedom of movement of the pipeline may be considered by applying lightweight compressible synthetics. Its application may only occur where no additional risk can occur for water management projects.

The synthetics must be made for the type of structure being considered for application.

The elasticity modulus of the synthetics to be applied must be low (E ( 1 N/mm2).

The compressive and tensile strengths may not be exceeded in the course of time.

The material must be able to withstand hydrolysis and mold.

COMMENTFor now only cell rubber (foam rubber made of butyl rubber with 100% closed cells) is deemed suitable for this aim.

Hardening

Use can be made of an injection method for soil with a chemical product that is suitable for the purpose to ensure that the crush pressure of the pipeline is diverted sideways and/or the bottom pressure is spread.

An adverse side effect is that the coefficient of soil reaction also increases.

Sand and gravel-containing sand can be considered for application: clay and peat soils are not suitable for injection.

Fixed layers (sand) must be present under the ground to be treated. Mild layers (clay and peat) will lead to subsidence.

Before switching to chemical injection, a ground investigation must be performed to obtain insight into the particle distribution of the ground and the composition of the layers to be injected.

In order to avoid increasing the volume mass of the ground too much, the volumetric mass of the chemical injection liquid must not be much heavier than the volumetric mass of water (approx. 1050 kg/m3).

The best result is obtained in ground that has not been agitated in connection with the regular distribution of the injection agents whereby the top injection level must lay at least 0.75 m below grade.

COMMENTIf there is less cover, it can be considered possible that the chemicals will not arrive at the required location due to the formation of leakage paths. Injecting in a backfill can lead to less adequate results due to irregular packing density (leakage paths) and contamination.

The effect of the injection on the state of the ground must be checked using cone penetration tests and sample boring. The petrified sand mass can also be excavated for inspection.

Compaction

The following applies in order to be able to deem the backfill as compacted when the trench backfill next to the pipeline has to be compacted (see also D.3.5 for the other requirements) for more sideway support pressure.

The backfill soil is sand that is placed carefully in the dry trench and is compacted mechanically in layers at a maximum of 30 cm. This is continued up to a minimum of 0.15 m above the crest before the trench is backfilled with other soil and compacted if required. The percentage of the maximum proctor density is larger than or equal to 94%. This must be proven with manual cone penetration tests. The backfill will be deemed not compacted within the framework of this standard if the percentage is lower.