In oil and gas deepwater pipeline projects, the welding of fatigue-sensitive Steel Catenary Risers (SCR), Corrosion Resistant Alloy (CRA) pipes and flowline pipes to tight specifications is critical. Counterboring the pipes might not be a viable method of controlling pipe geometry due to cost considerations or to limitations on pipe wall thickness. So how can a pipeline contractor ensure that the pipe fit-up, welding and pipelaying processes run smoothly with minimal interruption? How can a pipeline installation contractor be certain that all the pipes for a project are within the manufacturing specification? And, if they are, how easily will these pipes fit together prior to welding and pipelaying in order to minimise disruption in the welding and pipelaying process?
To prevent these kinds of bottlenecks, save costly delays and to minimise project risk, oil industry owners, pipelay installation contractors and welders need to capture, record and analyse pipe end geometry quickly and accurately. This measurement data, if used correctly, can then help to ensure that pipes delivered into the bead stall will fit together easily and within the welding specification requirements.
End dimensioning and fit-up typically involves two steps: measuring and fit-up. Measuring involves actually collecting pipe measurement data. Automatic, laser-based measurement tools can be used to measure geometrical features of pipe ends, normally performed onshore, although this process sometimes needs to occur on a cargo barge.
Laser-based measurement tools can be used to measure the IDs, ODs and WTs of pipe ends in rapid time. Typically, several thousand ID and OD measurements of a pipe end can be measured simultaneously in less than 10 seconds, enabling hundreds of pipe ends to be measured in one shift. In some circumstances, pipe ends can be measured in stacks. This means less time on site, less pipe handling (reducing costs), minimising delays and costs for the pipelay contractor. Laser measurement tools are also very accurate (typically to 0.05mm).
Data from laser measurement tools can then be made available to pipe optimisation software, which will include some sort of simulation or sequencing software. SmartFit™, for example, uses pipe measurement data to predict and control the fit-up, before the pipes are brought into the bead stall for welding. This averts production issues relating to poor fit-up and manages the assembly of problem pipes in order to maximise welding productivity.
Measure, mark and fit-up
Each pipe end is measured, identified and entered into the software. The software analyses the fit-up of pipes and allows the operator to mark the best rotational position on each pipe end. In the bead stall, these marks are aligned to immediately achieve the best rotational position so that misalignment is minimised and the project HiLo is easily achieved.
Any problem pipes that won’t fit at a specified HiLo are also indicated and are re-sequenced or removed completely so that fit-up problems do not occur in the bead stall. Production delays due to mismatched pipes are avoided.
Experience shows that with typical flowline HiLo limits – and using typical seamless line pipe that has not been counterbored – fit-up issues can occur regularly. For a HiLo of around 1.0 to 1.2mm, problems are likely to occur every 10 to 20 pipes (this varies according to the exact type of pipe). Using SmartFit™ pipe optimisation & simulation software enables the required HiLo’s to be achieved in the bead stall without trial and error. It also identifies up front problem pipe so that this can be removed from the pipe welding sequence, therefore avoiding any problems in the bead stall.
OMS has performed pipe measurement and fit-up surveys for customers located in every geographical region of the world, from the frozen Arctic areas of Russia to the hot humid conditions of the Middle East, Australia and the Gulf of Mexico.
In 2013, for example, OMS completed a pipe measurement and fit-up survey for the Gorgon Upstream Jansz Scarp Crossing near Australia. The laying of production pipelines between Barrow Island and the Gorgon and Jansz-Io gas fields was critical, as this section of pipeline crosses the Jansz shelf escarpment – one of the most significant challenges on the Gorgon project’s offshore scope. This involved laying three pipelines in 200m of water at the top of the escarpment down to a water depth of 730m. Due to the increased water flow pressures across the escarpment, the 30" diameter pipes are highly fatigue-sensitive. The welding of these pipes to precise engineering tolerances was therefore critical.
OMS conducted a pipe measurement and fit-up survey to ascertain which pipes would be suitable for the Jansz Scarp section of the pipeline and in which sequence these pipes should be welded in order to minimise project HiLo.
In order to prevent bottlenecks during welding and to minimise project delays and risks, OMS captured, recorded and analysed pipe end geometry quickly and accurately. This measurement data was then made available to SmartFit™, which then calculated the optimum sequence for these pipes before they were delivered into the bead stall for welding. This ensured that the pipe ends would fit together within the welding specification requirements.
Two OMS operators were deployed to Australia to carry out the onshore inspection of pipes. Using OMS’ PipeChecker™ laser-based measurement tool, the operators measured the geometry of the internal walls of more than 400 pipe ends. This resulted in around 70 pipes being selected as the most suitable (i.e. well within the manufacturing tolerance) for the Jansz Scarp Crossing pipeline. This pipe measurement data was then made available to SmartFit™, which was then able to calculate the best possible fit-up sequence for the pipes.
For this project, the HiLo requirement was less than or equal to 0.5mm. The weld seam had to be within +/- 45 degrees of TDC. In addition, the longitudinal weld seams had to be offset to at least 100mm. This data was configured into SmartFit™. The software analysed the fit-up of the pipes and allowed the operators to mark the best rotational position on each pipe end. In the bead stall, these marks were then aligned to immediately achieve the best rotational position so that misalignment was minimised and the project HiLo was achieved. Any problem pipes that didn’t fit at the specified HiLo were also indicated and re-sequenced or removed completely so that fit-up problems did not occur in the bead stall. Production delays due to mismatched pipes were therefore avoided.
As well as using SmartFit™ to optimise the sequence of pipe ends, OMS also managed the pipe sequencing process onboard the pipelaying vessel. This ensured that the correct pipes were brought into the bead stall in exactly the right sequence. In terms of the project’s engineering and environmental restrictions, this fit-up survey has been the most challenging for OMS to date. However, OMS delivered on time and within budget and the customer was delighted with OMS’ efforts.
Barzan Gas Project
In the Middle East, OMS completed a pipe end dimensioning and fit up survey for RasGas, a Qatar-based joint venture between Qatar Petroleum and ExxonMobil. OMS was contracted by RasGas and its pipeline contractor to perform an onshore pipe end dimensioning survey of more than 2,000 pipe ends destined for use on the Barzan Gas Project offshore from Qatar.
Two OMS engineers were deployed to the pipe-coating yard in Ras Al Khaimai, UAE, to measure the pipes. The 32” diameter pipe ends were long seam welded pipes with a 30mm concrete coating. OMS measured the pipe ends (in batches of 400 at a time) in order to identify 2,000 pipes that were ‘fit for purpose’ i.e. would go together within the project’s specified HiLo of 1.0mm.
Certain weld seam restrictions were also placed on the pipes. First, the long seam welds located in the upper quadrant of the pipe had to be within +/- 45 degrees of the vertical. Second, successive long seams were to be rotated in such a way that they were not less than 30 degrees from the previous weld seam. OMS performed several different scenarios in order to ascertain the optimum pipe fit up.
As the batches of pipe were end dimensioned and the "fit for purpose" pipes marked up accordingly, the measurement data was made available to SmartFit™ back in the UK. Overnight, the data was processed and the pipes were sequenced by the software so that the most closely matched ends could be brought together for welding. This information was sent back to OMS engineers at the coating yard, who then managed the process of physically locating the correct pipe ends in the yard, adding suitable rotation marks to the pipes. OMS also managed the loading of these pipes onto the pipelay barge in the planned sequence. Overseeing this process was absolutely key to the success of the project. This rapid turnaround - measuring batches of pipes during the day, followed by overnight processing and sequencing of the measurement data – prevented production delays due to mismatched pipes, leaving a very happy customer.
In 2011, OMS completed a pipe measurement and fit-up project for McDermott on the ExxonMobil/Neftegas-operated Sakhalin Arkutun-Dagi oil and gas field project in Russia. Once again, by using its SmartFit™ system, OMS avoided any pipe fit-up problems, providing McDermott with fast, good pipe fit-ups ready for the welding stage.
Sakhalin-1's Arkutun Dagi field is located off the northeastern coast of Sakhalin Island in the Far East of Russia. Operations and facilities are located on both the island and mainland Russia. The Arkutun-Dagi development will employ an offshore, ice-resistant fixed platform which is expected to become the largest oil and gas production platform in Russia.
Part of McDermott’s work scope for the project was the installation of a 20" Water Injection line, comprising of 1,978 joints of 20" x 33mm WT linepipe and 21 joints of 20" x 36.3mm WT linepipe. Prior to OMS’ involvement, portions of this line had already been installed by McDermott during a ‘Beach Pull’. McDermott contracted OMS to proactively manage pipe fit-up for the remainder of the project. This was a challenging project due to the need to achieve stringent fit up for a high pressure line in a seismically-sensitive region.
OMS deployed four personnel to Sakhalin from 13th September to 10th November 2011. These personnel used OMS’ PipeCheckerTM laser-based measurement tools to measure the geometry of the internal walls of more than 3,000 pipe ends. SmartFitTM was also used to optimise the sequencing of pipes on board the barges prior to the firing line.
Pipes were measured onshore at Kholmsk and at the pipe lay site, on board the Crest 289 material barge, the Maritime West material barge and the DLB-KP1 laybarge.
Pipe measurement data was made available to SmartFit™ onboard the pipelay barge. This comprised a laptop located prior to the firing line. All pipes brought on board the laybarge were identified and logged into the software. This enabled the pipes to be sequenced so that the most closely matched ends were brought together for welding. Pipes were then loaded into bevelling in the planned sequence.
Rotational positions for each pipe end were also determined, to put adjacent pipes into the best relative rotational position in order to minimise HiLo. Rotation marks were added to pipes, allowing the optimal rotation to be achieved when pipes were brought into the bead stall. Production delays due to mismatched pipes were therefore avoided.
The arctic conditions in Sakhalin means that the ocean freezes over in October or November. It was therefore critical that OMS completed its measurement and fit-up work on time. If it hadn’t, or if the fit-up was not optimised for McDermott’s welders, the ocean might have frozen over before the pipe could be laid. Heavy lift vessels had already been booked for Spring 2012 to perform work on the platforms. If the pipeline was unfinished, the window of opportunity would have been missed for one year. Without using SmartFit to optimise pipe fit up, a much larger quantity of pipes would have been rejected and it would have been very difficult to complete the project on time. As Robert McLean, Project Quality Manager at McDermott states: “OMS did an outstanding job for us on the Sakhalin project. Without doubt, we would not have managed to complete and lay the pipe water injection line without the valuable contribution and expertise of OMS engineers."
Hugh Davies, Director of Client Solutions, Optical Metrology Services (OMS) Ltd.