Elevator cable brittle fracture investigation

Recent consulting query — investigator saw brittle wire failures in an elevator cable but couldn't find intergranular fracture, so was reluctant to call it hydrogen embrittlement. Tom's point: piano-wire-class wire has been deformed so much the grains are wavy, so intergranular fracture is not the diagnostic indicator it normally is.

So this guy was looking at failures of an elevator cable, and he wanted to know — he had looked at the failures and they were somewhat brittle failures on some of the wires. One of the things you always suspect when you have brittle failures in steel is hydrogen embrittlement. He says, but we didn't see intergranular fracture. I said, of course not — the thing's been deformed so much, those grains are all wavy-shaped grains. You're not going to see intergranular fracture on a piano wire. This is only the second time in a month I've had to explain this. I can't tell you about the other one because it had to do with an aircraft — people were looking and they thought it was hydrogen embrittlement but they couldn't find intergranular fracture, which is characteristic of hydrogen embrittlement. It's not characteristic in piano wire because you don't have grains that are well enough shaped to give you intergranular fracture. This other thing, basically a very high strength steel similar to what they use in aircraft landing gear — it wasn't an aircraft landing gear, it was an aircraft application, I can't tell you more right now — probably was hydrogen embrittlement, but you can change the chemistry of the steel and you don't always get intergranular fracture with hydrogen. Ninety-eight percent of the time you do, so these people are thinking, well, I don't see intergranular, it can't be hydrogen. You need to know about the other 2% sometimes.