Folds vs cracks on tank threads?

[crpntr133]

How many good threads there are is the real question unless it is truly a crack.

 

[muddiver]

A fold is where the metal actually folds upon itself but is structurally intact. A crack is a structural failure where the metal's crystalline structure (how the metal binds to itself) is failing. Folds are quite common. An eddy current test should be used if a question of crack or fold is encountered.

If you plan to keep the cylinder, I reccomend you have it eddy curent tested to verify that it is not cracked. The inspector should have done that right after finding a visual indication. I was under the impression that eddy current was a standard PSI test. One of the shops I go to does it with every visual, probably over kill, but safe.

I agree that if the manufacturer offers to take it back, return it and get a blemish free cylinder. Or you might have to go throuhg this again with the next inexperienced inspector.

 

[oxyhacker]

There is a further distinction probably worth mentioning as it sometimes gets overlooked, between folds and valleys. The difference being that a valley is gradual, so you can see the bottom, where a fold is sharp, so you cannot. Folds and valleys used to be treated pretty much the same, but now valleys are regarded with much more suspicion, since they can conceal cracks or act, due to their sharpness, as stress risers and crack starters. So while some inspection protocols still tolerate folds as long as they do not cross more than one thread and no cracking is present, valleys may interrupt multiple threads as long as they are not too deep and the required minimum number of continuous uninterrupted threads remains (8 for 3000 psi tanks).

A fold is where the metal actually folds upon itself but is structurally intact. A crack is a structural failure where the metal's crystalline structure (how the metal binds to itself) is failing. Folds are quite common. An eddy current test should be used if a question of crack or fold is encountered.