Additive Manufacturing Symposium

Structural Integrity Technical Group Meeting

Offshore Oil and Gas Technical Group Meeting

Advances in Particulate Engineering for Defence, Safety and Security Applications

Visit our website to find out more.

Connect+ is the electronic newsletter from TWI. This regular e-mail publication showcases a selection of news and technical information but for an expanded view and access to a wider collection of recent papers, please visit our Connect+ webpage: www.twi-global.com/news-events/connect-plus/

TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK Tel: +44 (0)1223 899000

Connect+T h e m a g a z i n e o f T W I

TWI 2016 Events

Autumn 2016

TWI’s Middlesbrough Technology and Training Centre has moved into its new home – the flagship building in the new Teesside Advanced Manufacturing Park.

The move was planned and executed in a way that ensured minimal disruption to TWI’s Members, who can now benefit from the greatly enhanced capabilities available from the new building.

Constructed in partnership with Middlesbrough Council and the Tees Valley Combined Authority Local Enterprise Partnership, the purpose-built facility represents a sizeable boost to engineering consultancy and industry training capability in the Teesside region.

Training services available from the new centre include underwater inspection – delivered in a large dive tank equipped with modern diving apparatus – a dedicated plastics joining facility, weld inspection and the full suite of non-destructive testing techniques.

Engineering services are provided from a bespoke engineering hall, designed and equipped with a particular focus on thick-section welding and electron beam technology to support the offshore and fabrication industries.

Companies in the region can also benefit from extensive materials characterisation and modelling services, including advanced surface characterisation, weld modelling, fitness-for-service assessments and additive manufacturing simulation support.

The Ferrous Road facility also houses an office for TWI Certification Ltd, from where compliance verification engineers, all of whom are professionally qualified and experienced welding engineers, deliver assessments of manufacturers and training providers against European and international standards.

The new facility is located in the Teesside Advanced Manufacturing Park on Ferrous Road, just a few hundred metres from TWI’s previous Riverside Park address. TWI is operating the new building with an open access policy for local companies and TWI Members interested in finding out about available services.

The phone number for TWI in Middlesbrough is unchanged: 01642 216320.

New home and new capabilities for TWI in Middlesbrough

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Autumn 2016

New Members of TWI

Bombardier Recreational Products IncCanadaManufacturer of recreational vehicles

Brose LtdUnited KingdomManufacturer of seat assemblies and window regulator and door systems

CamdenBoss LtdUnited KingdomSupplier of electronics components and equipment

CRRC Qingdao Sifang Co LtdChinaRolling stock manufacturer

Daihen CorporationJapanProduction and sale of welding machines and industrial robots

DNA Electronics LtdUnited KingdomGenomics specialist

Etalim IncCanadaDeveloper of renewable power generation equipment

Europipe GmbHGermanyManufacturer of large-diameter steel pipes

Henrob LtdUnited KingdomDeveloper and supplier of fasteners

Hitachi Air Conditioning Systems LtdJapanManufacturer of air conditioning equipment

Huntingdon Fusion Techniques LtdUnited KingdomManufacturer of weld purging equipment

Hunan Joinfront Welding Technology Co LtdChinaProvider of welding and joining services

IPP Mardale LtdUnited KingdomSupplier of subsea fabrication solutions

Johnson & Starley LtdUnited KingdomManufacturer of heating and ventilation products

Livbag SASFranceManufacturer of airbag inflator systems

Meggitt Control Systems BirminghamUnited KingdomFabricator of heat exchangers for aerospace

Meritor Aftermarket UK LtdUnited KingdomSupplier and repairer of truck and trailer braking and suspension systems

PetroChina Pipeline Research CentreChinaManager of onshore pipelines

Powergen Technical Services Pvt LtdIndiaDesign and engineering consulting service

SABCABelgiumManufacturer of aircraft structures and systems

Sulzar Pumps EquipmentSwitzerlandSupplier of pump equipment

Taylor Studwelding Systems LtdUnited KingdomSupplier and manufacturer of studwelding equipment

United Construction and ManufacturingUnited KingdomFabricator of steel stairs and banisters

United Launch Alliance LLCUnited States of AmericaFabricator of spacecraft launch vehicles

VTCO Petroleum ServicesEgyptEngineering solutions for the oil and gas sector

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January/February 2014

High-pressure hydrogen testing at TWIIn a secure building located a safe distance away from the main buildings at TWI’s headquarters can be found TWI’s high-pressure hydrogen testing facility.

Behind its blast doors, this building houses two pressure vessels capable of carrying out mechanical testing on components exposed to pressurised hydrogen gas at temperatures ranging from -50°C to +85°C. One can generate pressures up to 450 bar – the other up to 1000 bar.

While in these atmospheres, parts can be exposed to compressive and tensile loads, either statically or cyclically at frequencies up to 5Hz. The facility can also be used for hydrogen pre-charging, in which components are exposed to hydrogen gas at high pressures and temperatures for extended periods.

Supported by a complete range of analytical equipment including scanning electron microscopes (SEMs), TWI uses the facility to provide detailed analyses of the behaviour of materials during exposure to hydrogen gas.

Analytical capability also extends to measuring materials’ hydrogen content. Coupled with high-temperature charging, this data reveals materials’ susceptibility to internal hydrogen embrittlement – information essential for applications in sectors including power, aerospace and automotive.

The future: a unique new test rig for the aerospace industry

With a decade of hydrogen testing behind it and such specialised equipment, TWI has become a trusted partner for companies from industries including aerospace, automotive and steelmaking.

Recently, however, Industrial Members in the aerospace sector have been expressing interest in new test types that cannot be conducted using the existing equipment. TWI, with its history of creating bespoke test rigs, has responded by launching a joint industry project to explore the feasibility of constructing a unique new test vessel capable of carrying out a greater range of tests.

The proposed vessel would support temperatures exceeding 1000°C and pressures up to 1000 bar, with mechanical test types available including tensile, fatigue crack growth rate, strain-controlled low-cycle fatigue, fracture toughness, cyclical at 20Hz, and testing with a negative load ratio.

If found to be viable, the new test system will enable tests to be conducted that provide industry with enhanced assurance of component performance. However, the team building such a rig would have to overcome a large number of potential design issues.

These include the demands the high pressures, temperatures, and test frequencies would place upon the pressure sealing system; the increased potential for hydrogen diffusion, attack and embrittlement; the challenges of implementing associated instrumentation; and the need to incorporate dedicated heating and cooling systems.

The joint industry project will conclude next year.

In a separate development, TWI is also exploring the possibility of adapting its test facility to enable the study of material performance in liquid hydrogen environments. This would address the needs of Members in the space and automotive sectors.

For more information on either of these proposals, or about TWI’s hydrogen testing services, contact us.

Autumn 2016

Job Knowledge 141 - Full-Scale Fatigue Testing using the Resonance MethodIntroduction

As described in previous Job Knowledge articles welds have a low fatigue strength. S-N curves, published in standards such as BS 7608 or DNV-RP-C203, describe the fatigue strength of welded details for different combinations of weld geometry and applied loading. When a designer specifies a new welding procedure they must be confident that these new welds will have sufficient fatigue strength to survive the applied cyclic service loads without cracking. This is particularly important in structures with no redundancy in the design, such as girth welds in risers and flowlines.

Girth welds can have a wide range of fatigue strengths. Those made on a backing bar are BS 7608 Class F2 details whereas ‘defect-free’ girth welds with the weld caps ground flush are BS 7608 Class C details - this difference can result in as much as a factor of 10 on fatigue life for a given stress range. In addition to these weld-design considerations, there are many other factors which influence a weld’s fatigue strength which are less easy to control. These include weld profile, joint misalignment, the presence of defects and residual stresses. The way in which each of these factors influences the fatigue behaviour of a weld is difficult to predict. Therefore, the safest way to determine the fatigue strength of a girth weld that has been made using a new welding procedure is by testing representative specimens. This way, designers can gain confidence that the welds produced will withstand the expected service loads or that they will be at least as strong as the required design curve.

Options for determining fatigue strength

There are two main methods to determine the fatigue strength of girth welds through testing. One is by extracting strips from pipes and then testing these in hydraulic test machines. These tests are usually run at a frequency of up to 5Hz and can be run at high stress ranges and in environments other than air. However, when strips are cut from pipes containing girth welds, the residual stress profile is no longer representative of the complete joint and the specimens produced may not contain the most fatigue-critical section of the girth weld. This can result in an over-prediction of fatigue strength

(particularly in the high cycle regime) and fatigue limit (Maddox and Zhang, 2008).

The alternative is to perform full-scale fatigue testing. The main benefit is that the whole girth weld, in its natural as-welded condition, is subjected to the fatigue load cycle. Conventional test methods require huge load capacities, but for testing in rotating bending the resonance method is a fast and energy-efficient approach. It is also a very efficient method for determining the fatigue strength of other tubular structures such as pipes with polymeric coatings and mechanical connectors. The test frequency is high, at around 30Hz. There is no standard that defines a resonance fatigue test; however, TWI has over 15 years’ experience of running resonance fatigue testing programmes.

The principle of resonance fatigue testing

Resonance fatigue testing involves exciting a test specimen close to its first mode of vibration by applying a rotating radial force to one end. A bending moment is generated in the specimen, which rotates about the pipe axis, resulting in all of the longitudinal fibres in the specimen experiencing the same bending moment during one revolution of the excitation force (Figure 1). The specimen vibrates in the first mode, and so there are two locations along the specimen length at which there is no deflection. Specimens are supported at these nodal points.

Figure 1 Schematic showing the principle of resonance fatigue testing (in two dimensions). In practice the spinning applied force causes the specimen to precess in a circular orbit.

Along the specimen length, the bending moment is a maximum at the mid-length and decays to zero at the specimen ends, as shown in Figure 2.

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January/February 2014Autumn 2016

Figure 2 Bending stress (or alternatively bending moment) profile in a resonance fatigue test specimen with a circular cross section.

The resonant frequency of a test specimen depends on the specimen’s mass and stiffness, and therefore the outer diameter and wall thickness of the pipe being tested. Specimen lengths are chosen so that they have a resonant frequency of around 30Hz. At this frequency, approximately 2.5million cycles are applied to the test specimen in each 24 hour period. TWI’s resonance test machines can accommodate pipes in the range 8in to 36in outer diameter. Typically, 8in outer diameter specimens are around 4.5m long and 36in outer diameter specimens are around 10.5m long (Figure 3).

Figure 3 Four of TWI’s resonance fatigue test machines, capable of testing pipes with diameters ranging from 8in to 24in.

Tests are run below the resonant frequency so that the applied stress range can be carefully controlled (Figure 4). By altering the speed of rotation of the excitation force (which in practice is achieved by altering the motor speed), the deflection and therefore strain range can be controlled.

Figure 4 Resonant response showing how the specimen deflection is controlled by altering the speed of rotation of the excitation force.

Practical considerations

The applied strain is monitored using strain gauges that are located in the area of interest (Figure 5).

Figure 5 Uniaxial strain gauge applied to a pipe, and used to control and monitor axial strain applied during the resonance fatigue test.

When qualifying girth welds to determine whether their fatigue strength is at least as good as a particular design S-N curve, the nominal applied stress range is needed. In order to measure the nominal stress range, strain gauges are positioned such that they are remote from the weld to avoid any secondary bending stresses associated with misalignment at the joint, but close enough that they are not significantly affected by the decrease in applied bending moment remote along the specimen length (as shown in Figure 2). A distance of 60mm from the weld toe is the ideal strain gauge location for this purpose. The resonance method is capable of applying nominal stress ranges between around 50MPa and 250MPa.

The resonance test method applies a fully alternating stress cycle with a stress ratio, R, equal to 0. However, since the residual stress profile in girth welds is difficult to predict it is important that a high

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January/February 2014Autumn 2016

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tensile mean stress is applied to them during fatigue testing so that the results are conservative. In almost all cases, a mean stress which is at least half of the highest stress range used in the tests is applied to specimens by internally pressurising them with water. This produces a positive R-ratio and so ensures that the full applied stress range is tensile.

The added benefit of using internal pressure to apply a mean stress is that it also acts as a means of crack detection, and so resonance tests are set up to stop automatically when the internal water pressure drops due to the presence of a through-wall crack. At TWI, alternatives to using internal pressurisation include carrying out tests with a mechanically applied tensile or compressive mean load, or with cooling water flowing through specimens.

When cracking occurs, stresses redistribute and this can also be detected by strain gauges located close to the crack position. The ability to detect cracking via the strain gauge readings is particularly useful in complex connector specimens in which, for example, a crack may initiate in a location which does not result in a drop of internal pressure, or in specimens tested with a mechanically applied mean stress rather than internal water pressure.

Typical test programmes

In a resonance testing programme to qualify girth welds, engineering judgement is used to select the number of specimens to test. The industrially accepted approach is to test nine specimens, three at each of three stress ranges.

In a typical test programme, high and medium stress range tests would be run until through-wall cracking occurred, while low stress range tests could be stopped as ‘runouts’ (above the target life but before cracking has occurred). The results from cracked welds would then be compared to a target curve which is based on a design S-N curve (from BS 7608 or DNV RP C203) and gives a specified level of statistical confidence that the results qualify to that fatigue class.

Written by Carol Johnston.

TWI Virtual Academy launches eLearning package for CSWIP 3.1 Welding Inspector

Students enrolling on the CSWIP 3.1 Welding Inspector course with TWI Training can now boost their chances of success by including a pre-course eLearning package.

The eLearning materials for CSWIP 3.1, have been in demand since the TWI Virtual Academy was launched. Comprising 11 modules covering every aspect of the course, the online add-on provides an excellent way of familiarising yourself with all the knowledge needed to gain internationally recognised CSWIP 3.1 certification.

The eLearning materials include videos, animations, images and interactive activities. Each module concludes with an assessment. Completing these assessments will bring to light any areas you are finding particularly difficult. You can then discuss these with your tutor when attending the week-long course, enabling you to make best use of your time in the classroom.

Opting for the eLearning package when enrolling has been proven to lead to better results. In a direct comparison, students who included the add-on when enrolling on the CSWIP 3.2 Senior Welding Instructor course outperformed those who did not.

Once you have enrolled you will have 60 days’ access to the eLearning materials, giving you plenty of time to work through every module and ensure you have a thorough understanding of all of the topics covered.

For more information visit the CSWIP 3.1 Welding Inspector Theory Pre-course eLearning Package course page, where you can access an interactive demo taken from the destructive testing module.

If you have any questions about eLearning with TWI, contact us via the TWI Virtual Academy website at www.twivirtualacademy.com.

Autumn 2016

Autumn 2016

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Case study: Full-scale sour fatigue testing machine for riser girth weldsTWI designed and built a unique custom rig capable of testing full-scale pipe welds in an internal sour environment, to support its Industrial Members in the oil and gas sector.

Steel catenary risers are commonly used within deepwater oil and gas developments, and fatigue performance is often a critical factor in their overall design. Resonance fatigue testing of full-scale girth welds has become standard industry practice to demonstrate adequate performance.

However, these tests alone take no account of aggressive service environments such as sour production fluids. In these instances qualification testing is usually a two-stage process involving full-scale resonance fatigue testing to demonstrate the required performance in air, and small-scale (strip) fatigue testing (in air and in the sour environment) to determine a fatigue life reduction factor that is then applied to the base design curve. This approach accounts for geometry effects (ie the difference between strip and full-scale testing) and environmental effects individually, and has been adopted on many projects. However, the validity of the approach had not been demonstrated, so TWI launched a JIP with that aim.

Breaking new ground

The project had several key objectives:

� Elimination of excessive conservatism, providing significant cost savings and greater design flexibility � Greater confidence in likely material behaviour in service, resulting from a more direct means of quantifying material

performance � Improved understanding of fatigue in sour environments, leading to enhanced safety by reducing the risk of corrosion

fatigue-related failure

Test machine

Phase one of the project involved the design and manufacture of a rotating bending fatigue test machine capable of testing full-scale pipe welds with an internal sour environment.

The machine incorporates several novel features:

� Orthogonal pairs of hydraulic actuators permit in-plane bending, rotating bending, or anything between the two, up to +/-250kNm bending moment.

� Large diaphragms support the pipe at its ends, permitting angular rotation while maintaining axial alignment. � A unique internal jack/column system allows up to 2MN of axial preload to be applied to the pipe. � An internal annular sour cell permits circulation of a controlled environment around the weld root region without

compromising the internal column system.

To discuss how this equipment could be used to support your business, contact us..

TWI Industrial Members now have a new supplier for their pressure testing requirements. In combination with TWI capabilities in project management, welding, specimen preparation, strain gauging, bespoke testing, fracture testing and resonance fatigue testing, the addition of a new purpose-built containment facility means that the organisation can provide a one-stop shop for full-scale component testing.

There is a growing need from industry for tests of pressure-containing equipment such as pipelines, risers and pressure vessels. These components are subject to complex loading conditions during their lifetimes, and highly specialised testing is required to accurately reproduce the environment in which they operate. While results from small-scale tests can to some extent be extrapolated to predict the behaviour of larger components, this method usually does not satisfy the safety concerns of oil and gas companies, who require the level of assurance only full-scale tests can provide.

In response, TWI designed, built and commissioned a new pressure containment facility, which enables large components to be subject to high internal and/or external pressure, in combination with axial or bending loads. The pressure pit facility is available for use now.

Capabilities

Applications for the pressure pit include:

� carrying out large, full-scale tests of components with internal water pressure to check for leak tightness and/or determine burst pressure

� performing proof of concept tests on new component design

� testing new connector designs in line with the requirements in ISO 13628-7 Annex I or API 17G

� carrying out bend tests on components containing internal water pressure of up to 29,000psi

� testing components under axial loads (static or cyclic) whilst containing internal water pressure.

The new facility is designed to safely apply axial tensile or compressive loads of up to 1500 tonnes (15,000kN) (static) and 500 tonnes (5000kN) (cyclic), and vertical loads on each of the cross beams up to 1000 tonnes (10,000kN) (static). Test fixtures can be designed which allow combined loads (axial plus bending) to be applied to components. During all of these load scenarios, internal pressures up to 2000bar (29,000psi), or external pressures up to 1000bar (14,500psi) can be applied to specimens inside the facility.

It is fully serviced by an overhead crane with two hooks of five tonnes each (ten tonnes total capacity). There are video cameras within the pit so that tests can be viewed remotely,

as they take place.

The facility adds to TWI’s existing capabilities of designing test machines, fixtures and fittings and so a range of specimen shapes and sizes can now be tested with internal pressure.

Specification

The pit is 3.7m wide and 3.45m tall. Its total length is 13.5 metres. A partition can be added to make two shorter containment facilities if necessary. It has a blast proof lid for containment of fragments and pressure, allowing burst tests to be carried out. There are a number of attachment points on all four walls, and I beams across the pit, and so tensile, compressive and bending loads can be applied to specimens. Components such as sections of pipeline and other pressure containing equipment up to 10m in length can be tested in the facility. Shorter lengths can be tested across the width of the pit.

To find out more about the specialised testing services available at TWI please see our website or contact us.

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January/February 2014

Connect+ is the quarterly magazine of TWIPhotographySimon Condie Production Kim BarrattJames Burton Graphic Design Craig Carter Copyright © TWI Ltd 2016Articles may be reprinted with permission from TWI. This publication is also available in alternative formats. To request a copy please contact marketing@twi.co.uk

Purpose-built pressure testing facility opens for business at TWI

Autumn 2016