Subsea pipeline tool fragment defect

A US-made seamless 4-inch, ~half-inch-wall pipe for an underwater Gulf of Mexico oil line passed mill hydrostatic, magnetic particle, and eddy current inspections. A 3–4 inch fragment of the piercing tool used in seamless-pipe manufacture had broken off and wedged into 80% of the wall thickness, plugging the defect so that hydrostatic tests passed. After welding, yellow corrosion coating, and ocean-bottom installation, a final hydrostatic test at lower pressure leaked — the wedge having loosened under prior tests. Recovery cost ~$4 million plus project delay. Tom uses it to illustrate that defects can survive multiple non-destructive and hydrostatic inspections by passing through critical-but-poorly-inspected zones.

How big can the flaws be? It's seamless, but how big can the flaws be in that piece of pipe in order to support 1500 PSI but have imperfections? They can be pretty big. I had a case down in the Gulf of Mexico where someone had a hydro test of a pipe made in the United States in a seamless mill, and they were going to put it in as an underwater pipeline in the Gulf to take oil from the drilling rig onshore to the refinery. It was only a 4-inch pipe, but it had been hydro-tested at the mill, magnetic particle inspected and eddy current inspected at the mill, and passed all those tests. They sent it down to Louisiana, sandblasted off all the information identifying the steel maker, coated it with this yellow coating for corrosion resistance because they were going to bury it in the ocean. They welded it, laid it down on the bottom of the ocean, and then had to do one last hydro test on the final assembly — and it leaked. It had already been hydro-tested and passed twice, and the hydro test at the bottom of the ocean was actually a lower pressure than the ones that had passed already. And there was a leak. Cost them $4 million to get it out of the ocean, bring it back, plus the delay in the project. Not everyone was happy.