Pipe welding problems solved?

Written by: Paul Fanning | Published:

Global expenditure on pipeline construction and servicing is expected to reach $216billion over the next five years, with over 270,000km of extra pipeline expected to be installed. However, one of the limiting factors in the lifespan of these pipelines is corrosion.

While Corrosion Resistant Alloy (CRA) clad pipe is becoming increasingly important in preventing corrosion, the welding process is critical to the successful fabrication of CRA clad pipes. By getting the process right it ensures minimised maintenance, reduced failure rates and extends potential operating life. In addition, large operators are now asking for tighter tolerances to maximise production life, and also to make the pipelines safer through better welds.

The result is that weld quality has become a high priority. To answer the industry demand, Hertfordshire-based Optical Metrology Services (OMS) has developed an internal weld inspection system to ensure the weld quality of joins.

A key focus for OMS was the dimensional measurement of oil and gas pipes and other structures where correct dimensions are critical such as military gun barrels, processing tubing and other manufactured industrial cylindrical objects. It wanted to develop methods of examining the quality of internal welds in detail, from both a visual and a measurement perspective, as existing methods had proven inadequate and unreliable.

"A considerable gap has existed in the technology for measuring the critical features of CRA welds such as HiLo (joint misalignment), weld height, width, and lack of penetration or fusion," says Hugh Davies, director of client solutions at Optical Metrology Services (OMS). "However, our OMS WeldChecker system comprises a high-resolution digital camera for video inspection, and a laser scanner to gather pipe geometry across both the pipes' inner walls near to the weld, and across the entire weld itself."

It is these parameters that have proven critical during Pre-Qualification Tests (PQT) for the welding process. By carrying out this inspection, OMS can better understand the welding parameters and show full compliance within the specifications typical of pipeline assembly.

"The ability to give closure on tough decisions regularly encountered by the welding inspector could prove invaluable in saving time," says Davies. "It also ensures only the highest-quality welds are accepted, leading to longer life of the welds and pipeline. However, timing is critical in order to maximise the benefits of the system.

"Video-only inspection tends to raise as many questions as it answers, often meaning that pipe joints need to be cut out to mitigate any risks, even if they turn out to be acceptable upon closer inspection later."

And while ultrasonic testing is available and very detailed, it can only be performed after the weld has been fully completed. This means there will have to be multiple weld passes before finishing the cap of the weld. As a result, if a flaw is found, it may result in many hours of work to put right, adding to the time and expense already wasted.

OMS has developed a inspection device it calls the WeldChecker. The device is placed inside the tubes and is able to move through the pipes and inspect the welds after just the second pass. If a flaw in the root weld is found, it can be cut out immediately saving time and money before it is too late.

Another challenge is the ability to inspect welds around curved pipes. Many of OMS' clients use CRA materials on subsea structures such as PLETs (Pipeline End Terminators) and PLEMs (Pipeline End Manifolds). These structures tend to have very tight bends, often as little as 1D.

"Assessing the lack of technology in the area, we designed and produced a new version of the WeldChecker that has the same design concept as a London 'bendy-bus' with a modular and flexible design," says Davies. "The advance in hardware has driven the capability forward, allowing previously inaccessible welds to be measured for compliance, guaranteeing they meet the specification."

Taking the technology to the next level, OMS has developed more compact tools that are now able to fit inside very small pipe diameters. It's now possible to deploy its WeldChecker in piping with a 100mm internal diameter. The development makes OMS the only company that can inspect welds using both laser measurement and visually at these small diameters and around tight bends in pipework.

So far the technology has been successfully deployed in a number of well-known oil and gas projects around the world. So where will internal weld scanning technology go from here?

"OMS is currently looking at the application of this technology in a number of different situations," says Davies. "One application is to mount the tool to the line up clamps for use in the critical welding path both onshore and offshore during pipeline welding. Another application is the inspection of tie-in welds on welded spooled stalks of pipe. This means while these pipes are spooled onto the vessel, the WeldChecker would be driven by a crawler. Finally, it could be used on older pipes and structures to measure the extent of corrosion or pitting, or to measure the extent of features in the pipe wall."

While innovative weld inspection tools are advancing, so too are the welding machines themselves. The issue of ensuring good welds, first time round, is a problem that is being addressed by pipeline assembly technology firm, Gridweld. The Birmingham company has developed an orbital welding system specifically to cope with the demand from the oil and gas sector.

Gridweld uses a specialised technique for joining pipes where the weld arc is rotated around 360° to seal the pipe joints, give a uniform weld thickness as well as overall quality. Gridweld has been set-up to provide orbital welding systems that are faster, lighter, and more efficient than existing machines on the market.

It developed a system called 'Scorpion', a lightweight automatic pipeline welding system that is capable of independent movement to enable the operator to weld steep gradients and accommodate differing pipe wall thicknesses. At just 16kg the device is much easier to attach to the pipeline band than heavyweight counterparts, and can be set up and operated by a smaller welding crew.

Welding passes can be re-selected during operation and the insulated shroud and shield assembly ensure tip replacement is minimal. The onboard control box enables welding parameters to be stored and the software can be upgraded onsite. Each device uses four brushed DC motors from the Maxon DCX family of configurable products to ensure precise and controllable movement.

The challenges of ensuring repeatable and quality welds in pipelines is an increasing area of importance and technological innovation as the industry looks to resolve many of the current issues experienced on the ground during construction.

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