For oil and gas companies, pipeline welding is a high precision task that cannot afford any delays. If pipes fit together poorly due to geometrical defects, this can lead to repairs and rework, which impacts tight production schedules.
In oil and gas pipeline projects, the welding of fatigue-sensitive SCR and flowline pipes to tight specifications is absolutely 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 pipeline contractors ensure that pipe fit-up, welding and pipelaying processes run smoothly with minimal interruptions?
In order to prevent bottlenecks during the welding process and minimise project delays and risks, oil industry owners, pipelay contractors and welders need to capture, record and analyse pipe end geometry quickly and accurately. This measurement data, if used in the correct way, can then help to ensure that pipes delivered into the bead stall will fit together within the specification requirements for welding.[Page Break]
Typically, end dimensioning and fit-up involves two main steps: measuring and fit-up. The measuring stage involves the actual collection of pipe measurement data.
Here, automatic, laser-based measurement tools can be used to measure the 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 and WTs of pipe ends in rapid time.
Typically, several thousand IDs of a pipe can be measured in less than half a minute, enabling hundreds of pipe ends to be measured in a single shift. This means less time on site, minimising project delays and costs for the pipelay contractor
Laser-based measurement tools are also very accurate (typically to 0.05mm).[Page Break]
Using tools such as these saves a lot of time. Being able to measure up to 400 pipe ends in a single day is at least three times faster than using regular, conventional measurement tools (eg caliper gauges), which only measure at a few discrete locations around the pipe.
Pipelay contractors are therefore able to keep their project schedules on track and because some projects involve measuring more than 2,500 pipes, the time and cost savings are significant.
Data from laser-based measurement tools can be made available to pipe optimisation software, which will include some sort of simulation or sequencing software, as is included in OMS' SmartFit program. This software uses pipe measurement data to predict and control the fit-up, before the pipes are brought into the bead stall for welding. This can avert production issues relating to poor fit-up and manages the assembly of problem pipes in order to maximise welding productivity.[Page Break]
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.
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 depending on the HiLo requirement.
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 project and the type of pipe). Using pipe optimisation and simulation software enables the required HiLo's to be achieved in the bead stall without trial and error. But when pipes will not fit, this will be indicated and the problem pipe can be taken out of sequence, therefore avoiding any problems in the bead stall. For a HiLo of 0.8 to 1.0mm, problem fits will occur in 20 to 50 per cent of the cases.
Many pipelay contractors are benefiting from working closely with experienced, independent measurement specialists such as OMS, helping them to avoid a range of potential issues such as wall thickness problems in SCR and flowline pipe, counterboring of SCR pipes and poor fit up on board 'J-lay' vessels.
OMS has already completed more than 30 major projects with customers using its SmartFit software, which optimises pipe fit-up and HiLo. SmartFit comprises a laptop computer system used prior to the pipe firing line, for example, in a 'ready rack' on the pipelaying vessel.[Page Break]
In a recent pipe fit-up project, for example, OMS project managed the complete pipe measurement, mark up and fit-up process, both onshore and offshore. After the pipes were measured onshore and marked up, they were transported by cargo barge to the laybarge. Using cranes, measured pipes were offloaded in small batches of 15-20 pipes to a pipe holding area on the main deck of the laybarge.
Here, an OMS inspector noted down the pipe numbers of the stack, creating a visual representation of the physical position, number and end designator of the pipes and whether any were 'anode' pipes.[Page Break]
Measure, mark and fit-up
Using SmartFit, the pipes were then sequenced to obtain best fit-up. The pipes were then numbered for the riggers. The riggers then loaded the sorted pipes in the correct sequence to the pipe bevelling inbound rack.
After bevelling, OMS inspectors marked up the pipes with rotation and datum marks. The spacer crew were then able to correctly align these rotation marks, which minimised the HiLo. This ensured that the project HiLo specification was met and that welding problems were avoided prior to the firing line.
Dr Richard Gooch is Director of Technology, Optical Metrology Services, Bishop's Stortford, Hertfordshire, UK. www.omsmeasure.com.