Girth Weld Cracks in Oil and Gas Pipelines Need Immediate Welding Inspection

13 March 2019

Girth welds, as the apparel-biased label implies, are those that go around something. Also known as circumferential welds, the fusing process joins pipe rims. Now, thinking like a welding inspector, someone who’s been hired to audit oil and/or gas pipeline junctures, girth weld cracks are a subject of great concern. For, as it turns out, there are pipes everywhere.

Oil and Gas Pipeline Weld Inspections

To be more precise, there are pipes all over an offshore oil rig. The pipelines travel to shore along the seabed, then on land. There are pipes travelling underwater, pipes running for hundreds of kilometres over land, and yet more pipes nestled inside oil refineries. To avoid expensive leakages, environmental damage, not to mention a potentially catastrophic combustion hazard, every pipe girth weld must satisfy a standardized flaw acceptance test, as carried out by a qualified weld inspector.

Girth Weld Cracks Require Immediate Attention

Because pipelines stretch across vast tracts of land, not every little flaw will get immediate attention. That would be a prohibitively expensive practise. No, by applying fitness-for-service models and fracture mechanics principles, a quantitative approach has been developed here, one that addresses current weld discontinuities and those that have a high probability of developing a pipe-weakening flaw. If workmanship standards are unsatisfactory or if a previously unseen weld discontinuity does breach that flaw acceptance threshold, then the girth weld defect isn’t just noted, logged and recorded. To the contrary, an immediate response is essential when such an environment imperilling fault is discovered.

A Final Thoughts Perspective

Girth welds travel circumferentially around pipes. They’re present on long pipeline stretches and sharp bends, where fluid stresses accumulate. In fact, there are a number of stresses at work here, such as longitudinal tension, which introduces the possibility of plastic collapse. Now imagine such defects developing in the field, perhaps below some remote mountain range or in the middle of an arctic wasteland. No matter the locale, though, the same truism applies: an oil or gas pipeline breach will severely impact the environment it stands within.

To deal with such far-ranging hazards, pipeline weld inspectors go looking for girth weld cracks. A drop in pressure has perhaps been detected, or maybe a technician has seen what he feels could be a series of hairline fractures. Not stopping to think about fracture mechanics models, the inspector hits the road and finds an access route to the defect. And it’s exactly the same on an offshore facility or a refinery, minus the days of road travel. The flaw modelling work will come, of course, but that phase takes place after a girth weld defects’ flaw acceptance criteria has been assessed.

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