Failure cause of rubber o-ring

[TED OH]

Hello All

All is well with you.

I got a Failured rubber(NBR) O-ring as soon as machine operated.
The manchine has been under 1.5bar and athmosphere temperature and it was not contacted any steam or water.
It had only some lubricant oil

I found out rubber o-ring had transverse failure mode as soon as dis-assembled manchine.

You guys can see the failure mode O-ring as below photo.
and I cut the failure part of O-ring

the surface of O-ring is very smooth but there are some porosity?

Could you please advise me the casue of failure and other reason?

 

[TugboatEng]

I see a similar failure on tube and socket fittings if the tube is not properly constrained. At every pressure cycle the the tube moves in and out which causes the o-ring to twist. Eventually it twists so much it tears through the center like this. There is usually a spiral shape to the tear in the case I have described so this may not apply to your situation. Explosive decompression creates a straight split like we see in your picture but that requires a rapid pressure change. I don't think 1.5 bar would so that.

 

[btrueblood]

That's a weird one. Agree with Tug, it might be decompression related, but hard to think how, unless it was subjected to a high pressure test with a gas (helium, CO2), maybe for leak detection... somewhere along the way. Another possibility is a mold defect, it almost looks like the rubber in the area is not fully cured.

 

[Tmoose]

Did you buy the machine all assembled from someone else, or build it?

Pictures and drawings of the sealed joint would be helpful.

The parker handbook ( and others ) have lots of information how to design static sealing joints, sliding joints, and rotating joints.
The requirements for o-ring cross section, o-ring compression, surface finishes, abutments and more are NOT the same for all joints.

if you bought the o-ring Does the o-ring supplier provide any documentation?