30-mile pipeline brittle fracture

Used to motivate the crack-stopper-ring application above. Brittle crack ran thirty miles in a gas pipeline before stopping.

Now, they did take that steel — it was a precipitation-hardened copper-nickel steel. It had fantastic mechanical properties. It just blew away most other steels in that strength range. They found niche applications as crack stoppers. A problem with steel — I'm not saying steel is the most wonderful material in the world, it's just the largest-used structural material — is that they have had brittle fractures in pipelines that run for thirty miles. An oil pipeline doesn't do that, because an oil pipeline is pressurized hydraulically, and the decompression wave in the liquid is faster than the crack runs. But in a gas, the decompression wave is slower than the crack — a brittle crack will grow at half the speed of sound, maybe fifteen hundred, two thousand meters per second. It sounds like a rifle shot. When that crack starts to go, it's a big bang, and it's moving at, let's say, 1500 meters a second. What's the velocity of sound in air at sea level? 343.6 meters per second at STP. I remember that from my high school physics. So 300 meters versus 1500 — the crack is always under tension as it's growing.

There have been cases — I've heard of cases — that there were small diameter pipelines, I don't know if they're 12 inch or whatever, where a crack would start and run for 30 miles in a buried pipeline, a brittle fracture. When I worked for Bethlehem Steel, they were starting to build the Alaskan pipeline, and Bethlehem Steel made big diameter pipe for pipelines, and there were other pipeline projects people were building in the world. The guy in the office right next to me was our pipeline expert at Bethlehem Steel. He was the one I think told me about the 30-mile-long running crack. They were looking at using inserts in the pipelines to prevent the fractures. Every couple of hundred yards they were going to weld in a heavy wall, high toughness steel. So this would be your regular pipe, but they might put a 12-inch-long piece that they would just weld in there that was thicker and very high toughness steel.

Referenced as the motivation for the 70 foot-pound running-crack-arrest specification. Gas pipeline; brittle crack ran 30 miles once initiated.

Originally, if you look at that Navy report, they found that in most of the ships that failed, the plates where the fractures initiated had less than five foot-pounds Charpy energy. The recommendation of the 1946 report was: you'd better have ten foot-pounds of fracture energy in that Charpy bar in order to avoid the brittle fractures and catastrophic failures. In the 1950s, when they started writing the code, someone decided we'd better put a safety factor on, so they upped it to 15. By the 1960s the Coast Guard said we'd better have a bigger safety factor, so they upped it to 20. By the time I was an engineer at Bethlehem Steel and people were designing the Alaskan pipeline, they were saying we need fracture toughness that will stop a running brittle crack. Because there had been fractures in pipelines where the fracture ran for 30 miles in the pipeline once the brittle fracture started. That gets expensive. So they wanted something that would stop a running brittle fracture. They were looking for 70 foot-pounds of fracture toughness, which is one of the reasons I was working on trying to come up with higher-toughness steels.