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How are these o-rings made and what is the cause of failure?

How are these o-rings made and what is the cause of failure?

(OP)
Click here for image album

This is a 26mm o-ring which failed after not much use. It was being exposed to 200 Bar every 30 seconds, 8 hours a day for a few days before failing.

I have two questions.

1. How is this sort of o-ring made? It looks like it has been rolled from a flat sheet but I cannot see a join. The last roll edge seal runs around the whole o-ring.

2. How did this fail? Is this a manufacturing problem or incorrect fitment?

Thanks

RE: How are these o-rings made and what is the cause of failure?

It looks like the o-ring got partially rolled. If one side was sliding on a surface and the other rolled. The result is that this part of the o-ring, where the sliding met the rolling, got twisted.

RE: How are these o-rings made and what is the cause of failure?

(OP)
So it wasn't manufactured from a flat piece of rubber? The roll is quite uniform which makes me think that it was made that way.

RE: How are these o-rings made and what is the cause of failure?

Classic spiral failure, cause is as Dougt115 described. See the Parker O-ring Handbook (google it) for more info.

RE: How are these o-rings made and what is the cause of failure?

(OP)
Ok yes, that explains it well. I didn't really think that was possible from sliding back and forth like that as the spiral cut is so uniform. So much so that I can almost unroll the o-ring.

Thanks guys.

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