Use of Flexible Data Acquisition on Cleaning Pigs for Offshore Applications Jan van der Graaf1, Dr. Hubert Lindner2 1ROSEN Europe B.V, Netherlands 2ROSEN Technology & Research Center (RTRC), Germany

Presenter: Jan van der Graaf Product Sales Manager ROSEN Europe B.V. Zutphenstraat 15 7575 EJ Oldenzaal The Netherlands

CV Mr. Jan van der Graaf graduated as a Mechanical Engineer from the Delft University of Technology in 1978, on the subject of model testing and numeric simulation of liquid and gas flow in carburettors. He has been involved with the pigging industry since then, from 1988 in various positions within the ROSEN Group of companies. In his present position of Product Sales Manager, the behavior of cleaning pigs, recommandations of bypass in pigging and application and interpretation of Pipeline Data Logger data are part of his activities.

1. Introduction The expanding development of offshore gas and oil reservoirs particularly in deep water areas are extending the challenges for pipeline integrity in design and construction as well as maintenance and inspection. The existing offshore pipeline systems on the other hand are undergoing significant changes in design and/or operating conditions. For example new tie-ins from new wells or massive declining flow rates. Considering the high importance of these systems and the high consequences of pipeline failures, the relevance of pipeline cleaning and inspection is obvious. Therefore a flexible data acquisition system applied with regularly operated cleaning pigs is a valuable intermediate step for pipeline monitoring below the level of In-line Inspection. The Pipeline Data Logger (PDL) measures physical values like accelerations (3 directions), absolute and differential pressure and temperature. Designed as an add-on for pipeline pigs, it can be used for nearly any type of cleaning and inspection tool. This paper describes the basic functions and design of the data acquisition system. Further some examples of real data achieved from offshore runs are presented to demonstrate and discuss the versatile options of the data interpretation.

7th Pipeline Technology Conference 2012

2. Measuring Technology The ROSEN Pipeline Data Logger (PDL) is designed as an stand-alone unit, which only needs to be assembled to nearly any type of pipeline cleaning or inspection tool. It is available in two sizes PDL 4 and PDL 14 and can be operated from 4” and larger with pressures up to 300 bar (High Pressure version) [1]. The PDL4 Professional tool carries the following sensors:

absolute temperature

absolute pressure (upstream)

differential pressure

acceleration in X, Y and Z axis.

The fast response sensors are measuring with a 500 Hz frequency. Data of each sensor are stored with an interval of 0.25 sec (programmable) as follows:

minimum value measured during the interval

maximum value measured during the interval

average value calculated of all measurements during the interval

In this way peak values are recorded regardless of their duration, so that no features are missed. The three traces are indicated by different. All recording is time based, and distance correlation of measured data is only possible indirectly when the tool is running at constant speed (with optional support of benchmarking information using tool transmitter for on-shore pipelines). The results of the PDL Inspection can be presented in the different graphs where some of the values are calculated from the basic measurements.:

Temperature Absolute pressure Differential pressure Acceleration (x, y and z-axis) Inclination (calculated from the accelerations) Rotation (calculated from the lateral accelerations)

Sensor Data Charts The data recorded are presented in the form of a chart covering the complete duration of the PDL runtime and optional enlargements of areas of special interest, such as launcher and receiver area as well as the restrictions. For the interpretation of the different charts, the combined effects of pipeline operation conditions (flow rate, pressure), tool configuration (stiffness, wear), pipeline geometry (profile, internal diameter variations, deformations) and pipe wall conditions (cleanliness) shall be taken into consideration. Please note that all charts are time based. Since the tool does not measure distance, no distance or speed information is recorded.

However, the recognition of the regular girth weld pattern in Differential Pressure and X-acceleration sensors does make an estimation of local speed possible. As the acceleration sensors are sensitive to both acceleration and gravity, this has to be considered particularly for the interpretation. It is even more important for inclination and rotation charts because these are calculated from the acceleration values.

3. Field of Application, Data Interpretation Possibilities Because of the easy and flexible use of the ROSEN PDL, the basic range of application is nearly unlimited. This also applies for the motivation to use such a device. A choice of this can be: - Measuring of the required differential pressure to pass the pipeline and/or certain

installations. - Measuring of the temperature profile to support wax or scale deposit modeling - Measuring of the differential pressure to monitor the progress of cleaning - Supporting gauge plate indication analysis to localize possible positions. - Evaluation of pig run behavior by acceleration and pressure data including pig

stops - Measurement of absolute pressure profile for detailed hydraulic evaluation and

monitoring of the pipeline system. - Determination of the differential pressure peak for bypass calculations, e.g. for

slug control purposes. The power of the interpretation can be increased by the combination of the various data channels. The interpretation software provided allows tiled display of the different measures as well as a convenient tool to select and synchronize time frames of particular interest. For example the absolute pressure trace is a good indication for the time range pressurization to depressurization and the inclination gives a precise view on the vertical and inclined parts of a pipelines. Based on these information, for example the differential pressure values for the platform piping and riser section can be assigned. The particular value for deep water application is not only based in the tool itself, but as much as in the missing alternative options. Besides the instrumented measurements of the relevant system the possibilities of inspection are limited and expensive. In most cases it would require the operation of a special supply vessel and a ROV. Therefore the benefit of this system becomes visible. Furthermore, the reason for an PDL inspection could reach from a single use because of a particular indication (e.g. changed operating characteristics, known damage or pre-inspection pigging) to a continuous monitoring of the pipeline system. The value of the information can be increased by the continuous monitoring of the measurements at regular cleaning runs. Opening the possibility to evaluate the development of the achieved data from run to run either by unchanging of varying tool design. Even if single run results of a continuous program are not particularly conspicuous, the difference may contain valuable information.

4. PDL Measurement Examples This section shows some comprehensive results of subsea pipeline PDL measurements. These are not necessarily showing critical or spectacular details, but shall give an overview about the properties of this tool and some of the experience. Please always keep in mind, that the PDL measurement is time based, therefore the x-axis is showing the time and not the distance as usual for intelligent inspection tools.

4.1 14”/18” Deepwater Pipeline For a challenging 14”/18” deepwater pipeline project [2] ROSEN has developed particular inspection tools as well as a gauging tool to run primarily for passage assurance. The pipeline is located between two platforms in a deep water area. To gain early information about this line, the gauging tool was equipped with a PDL. As a first view at the results Figure 1 shows a combined and synchronized diagram of the pipeline pressure, the differential pressure and the tool inclination. Further discussed areas of special interest are indicated. Figure 1: Combined overview of 14”/18” Gauging Tool run PDL data with indication

of discussed areas (x-axis grid 1 hour).

The top diagram in Figure 1 shows the absolute pipeline pressure measured by the PDL. It clearly indicates the time of pressurization and de-pressurization which give the time frame for the tool run. Following the three areas of interest are discussed: The launcher and riser, the subsea connection jumper and the receiver including riser. Therefore these areas are zoomed into a shorter time range.

4.1.1 Launcher and Riser The zoomed view of the launcher area (or around launching time) clearly shows when the tool is positioned in the launcher. This is can be found in the inclination diagram where the inclination changed from 0 deg to about 90 deg and keep this orientation in the vertical launcher for a while. About 10 minutes later, the launcher is pressurized (see absolute pressure graph). The actual launching of the tool is indicated in all three graphs (change in absolute pressure, increase of differential pressure including a high peak and some changes in inclination due to direction changes on the platform. Somehow unexpected may be the increase of pressure during the first 10 minutes of the run. This is because of the vertical movement of the tool and the hydrostatic pressure of the compressed gas. The vertical movement of the tool is confirmed by the smooth change of the inclination from 90 deg to about zero within these 10 minutes. For an evaluation of the behavior on the platform, the time range has to be enlarged again (Figure 3). Figure 2: Combined overview of 14”/18” PDL data from launcher and riser (x-axis

grid 10 minutes).

The zoomed view of the launcher area (or around launching time) clearly shows when the tool is positioned in the launcher. This is can be found in the inclination diagram where the inclination changed from 0 deg to about 90 deg and keep this orientation in the vertical launcher for a while. About 10 minutes later, the launcher is pressurized (see absolute pressure graph). The actual launching of the tool is indicated in all three graphs (change in absolute pressure, increase of differential pressure including a high peak and some changes in inclination due to direction changes on the platform. Somehow unexpected may be the increase of pressure during the first 10 minutes of the run. This is because of the vertical movement of the

tool and the hydrostatic pressure of the compressed gas. The vertical movement of the tool is confirmed by the smooth change of the inclination from 90 deg to about zero within these 10 minutes. For an evaluation of the behavior on the platform, the time range has to be enlarged again (Figure 3). Figure 3: Combined overview of 14”/18” PDL data of launcher platform (x-axis grid

10 seconds).

As the absolute pressure does not change during the launching operation, Figure 3 displays only the differential pressure and the inclination. The differential pressure shows a high peak of more than 6 bar at just at the begin of the movement. This is representing the reduction of the launcher which is in this case known to be narrow compared to the rest of the line. Furthermore one can see a reduction in dp about 50 seconds later indicating a change of pipeline structure (internal diameter, surface). At least two changes of the pipeline direction are shown by the two peaks in the inclination graph resulting from short horizontal parts. As the change of direction are not noticeable in the differential, the related bends seem to be not narrow (5D or larger). A nice additional measurement shows the temperature trace in this area in Figure 4. Starting with the high temperature of about 41 deg C, the temperature drops to 5 deg at the sea bottom in one hour. The sea bottom was reached after about half an hour. Figure 4: Temperature View around launching time (x-axis grid 20 minutes).

4.1.2 Subsea Jumper and Wye-Piece The second particular section of this survey is that of the subsea jumper as indicated in Figure 1. In this case, the leading diagram is that of the tool inclination because of the remarkable orientation changes in this area. Additionally the differential pressure is displayed in the following diagrams (Figure 5). Figure 5: Inclination and Pressure at subsea Jumper (x-axis grid 5 seconds)

The two jumpers are part of the 14” section of the line and include 4 bends each. The second jumper ends in a wye piece including the 14” to 18”expansion. It is clearly noticeable that the inclination trace is not smooth and symmetrical only in the first upward bend. This is confirmed by the high differential pressure at this point of time. Obviously the tool has stopped for a while building up differential pressure up to 3.2 bar. Then the tool re-starts passing the rest of the combination without any other remarkable feature. The comparison with the design drawings showed an internal groove in the pipeline resulting from a flexible connector. Most likely the front disc was caught in this grove as the rest of the tool was still in the bend. Therefore it needed some higher differential pressure to move again. As a possible consequence of this finding, the design of an inspection tool could be checked regarding this particular feature.

4.1.3 Riser and Receiver No particular behavior of the tool can be found in the receiver area displayed in Figure 6. Though the elevated crossing just before the riser bend is no standard combination. The riser pipe itself again seems to be different as the acceleration pattern has changed visibly. Running smooth in the subsea line it suddenly shows distinct acceleration peaks in a regular pattern indicating the girth welds. In many cases this pattern even allows a velocity estimation of the tool when the joint lengths is regular.

Figure 6: Combined overview of 14”/18” PDL data of riser and receiver (x-axis grid 25 seconds).

4.2 Identification of tool damage reason with PDL Like in the first example a wye-piece in the pipeline required a dual section cleaning tool to seal the open area in the wye (Figure 7). The cleaning tool was equipped with a ROSEN PDL to monitor the tool behavior. Figure 7: Two segment Cleaning and Gauging tool for long subsea gas line

After the run a damage on the front loose flange and the guiding disc was observed. Remarkably this was not on the first but on the second segment. Figure 8 shows a cut through the guiding disc and a scratch on the following cup. Even the loose flange has got a deep groove. At the bottom of the photo a second, but smaller

scratch on the guiding disc is visible. Although the damage was not really heavy, it has to be analyzed before intelligent inspection tools can be performed. Figure 8: Damage on front flange of the second segment of a cleaning tool Therefore the PDL data of the run was analyzed and a suspect measurement of the differential pressure was found shortly before the receiver. The inclination trace of Figure 9 clearly shows the onshore receiver bend combination. At the same time the differential pressure is increased likely due to a change of internal diameter and the valve passage. But earlier in Figure 9 an unusual negative differential pressure can be observed. Therefore this short time period was enlarged for further investigation. Figure 9: Unusual Behavior of Differential Pressure near Receiver (x-axis grid: 20

seconds)

A detailed view on the differential pressure in Figure 10 shows a negative pressure for a period of about 2 seconds with a minimum peak of -0.65 bar. At the same time the acceleration in longitudinal direction is also negative with a peak of -3.4 g. Whereas it has to be considered, that the PDL is mounted in the front segment and measures the dp only along this part of the tool. That a negative differential pressure creates a negative acceleration is logical, But what has caused the negative differential pressure? Combined with the short distance to the receiver and the damage pattern in Figure 8 a scenario becomes visible. Assuming that the main volume is still flowing through the branch of the tee and only a small amount through the kicker line, then the first segment of the tool runs in a almost closed gas volume when the front cup starts sealing. This means the front tool is decelerated to a lower velocity as the rear segment is still running with the original flow speed while sealing the main line. The tool actually bounces back. This causes high pushing forces on the universal joint which starts to jackknife. Directed by the side flow through the tee, the front of the rear segment is pushed towards the tee with the high forces and finally touching the guide bars. This constraint force is so high, that the polyurethane and even the steel flange is cut respectively damaged when sliding along the guide bars. Once the tool is decelerated to the velocity of receiver flow and the rear sealing element has entered the tee, the tool continues with normal run behavior (Figure 9). Conclusion: In order to prevent damage, especially in case of running a sensitive ILI tool, the production shall be fully diverted through the pig trap well in advance of the expected arrival time of the tool. Figure 10: Details of differential pressure and x-acceleration of Figure 9 (x-axis grid: 5 seconds)

4.3 Heavy wall riser bend detection in 6” line In a short 6 inch connection line the differential pressure trace of the PDL cleaning tool showed two distinct peaks in an otherwise smooth run (Figure 11). Further the gauge plate showed a heavy reduction of ID which was critical for the Inline Inspection Tool. Figure 11: Differential pressure measurement with 6” Cleaning tool

A detailed cut-out of the differential pressure compared with the inclination trace discloses the area and the reason of the high peaks. In Figure 12 the first of the two peaks is displayed. Figure 12: Detailed view on differential pressure and inclination

The profile of the pipeline as a connection between two platforms can be seen in the typical trace of the inclination in (Note: Positive inclination is indicating downward direction in this case due to calibration reasons). It started horizontally changing direction to a vertical movement with a short horizontal part in between as well. The differential pressure is almost constant besides a heavy peak in the area of the riser bend. With a detailed view is becomes clear that the differential pressure already increases before the inclination changes. This means the heavy wall part of the riser

bend already begins before the actual bend and ends later. Finally, the localization of the heavy wall part in the bend has prevented an otherwise very risky inspection survey.

5. Summary The paper presents the versatile and easy usable ROSEN Pipeline Data Logger (PDL). As an addendum to nearly all possible cleaning tools it can be used in a wide range of pipelines for an equally wide range of tasks. It reaches from single runs for a certain incident (dent or pre-inspection gauging) to a extended monitoring of the cleaning tool/pipeline interaction in regular cleaning. Because of the particular situation of subsea pipelines (high consequence environment, elaborate access, particular installations, multi diameter design) the PDL is an ideal measurement tool to support the existing Pipeline Integrity System, particular if regular cleaning is performed. The capabilities of the PDL are demonstrated by means of a series of examples. Consequently the paper discusses some features of the display software provided like synchronizing and zooming of the data. With regards to the basic application of this technology, the examples are intentionally presenting standard features of pipelines and not extreme situation like an external damage or similar. But just these generic samples using also the given information of the pipeline are demonstrating the helpful properties of the PDL in particular for subsea pipelines.

References [1] Van der Graaf, J.: Pipeline Data Logger – A new tool for the pipeline engineer. In: 3R

International Special Edition 13/2004 [2] Lindner, H.: Meeting the Challenge of Deep Water In-Line Inspection. In: International Oil

& Gas Engineer 02 – 2009.