Maximum groove dimensions 1

[HotStab]

Hi everybody,
The gland fill factor for O’ring seals is normally recommended from 60 to 85%.
Elastomer thermal expansion and swell are known reasons for restrictions of maximum fill. In other words, these issues impose minimum groove dimensions for a given O’ring section.
But, what about the minimum fill? Which are the governors for the maximum groove dimensions?
I would like to know what should be take in account to evaluate a groove improperly made bigger than specified.
I would appreciate any help.

 

[flexibox]

Can you advise the audience if it is a static Oring or a dynamic Oring groove in question? I think this may influence the reply you get.

 

[MikeHalloran]

_Evaluate_ a too- big groove?

Easy. It's scrap.





Mike Halloran
Pembroke Pines, FL, USA

 

[HotStab]

flexibox,
Regarding movement, it is a static application, but the seal will be submitted to pressure transients.
Operational pressure shall be around 3000 psi oil and gas. Temperature may be from 0oC to 82oC. Seal is fluorocarbon rubber 90 shore A.

Mike,
The groove has an improper width only. There is no compromise in its depth or in diametric clearance. Surface finish of all groove surfaces is according to specified.
Could you, please, explain your proposal of scrap damage?

Thank you both.

 

[flexibox]

If you have a width issue depending on degree of error I would install an anti-extrusion washer made of PTFE. Normally these are between 1mm to 1.5mm wide. You should consider this at those pressures anyway to prevent extrusion.

trust this helps

 

[flexibox]

Above reply assumes static Oring groove in shaft sealing a bore. If you have a static seal like a mechanical seal gland plate Oring sealing against the pump stuffing box then you should get away with a small width error because under pressure the Oring will be forced to the OD of the groove and providing you have the correct depth then it will be OK.

How much error do you have and what is the application, perhaps best you explain this too unless you have an answer now.

good luck

 

[MikeHalloran]

Extra width and pressure cycling risk spiral failures even in static seals, and the presence of gas makes a seal's life more interesting.

At that pressure, everything has to be perfect, and you should be using anti-extrusion rings anyway, so maybe you need a little more width to fit them.

Use two rings, so there's no chance of confusion about which side the ring should be on.



Mike Halloran
Pembroke Pines, FL, USA

 

[HotStab]

flexibox and MikeHalloran,
This O'ring is piston type assembled. It is used in a sealing sleeve between two parts of a subsea oil and gas production tool.
Despite the high pressure, according to our experience, we does not use back-up rings in this kind of application. If I prescribe a back-up ring to reduce width of one groove in one piece it may represent problems when that specific equipment will be submitted to disassembling for maintenance. Otherwise, to scrap the piece seems too much to me.
It’s not the first time I face this mismanufacturing problem, but I couldn’t figure out a failure mode that could be associate to a wider groove.
I agree that spiral failure may be a concern if O'ring is free to roll. But, the groove will be wider no more than 0.060" (in the specific case it will be only 0.030" wider) and it seems no serious threat.

 

[MikeHalloran]

Uh, "no serious threat"?

Downhole? Undersea?

What does it cost to replace a blown o-ring there?



Mike Halloran
Pembroke Pines, FL, USA

 

[EdDanzer]

When a seal groove is too wide, excessive wear on the seal and seal contact surfaces can result as the seal bounces back and forth in the groove. In o-ring bidirectional application I recommend narrowing the groove width and in some cases using a Quad ring to reduce movement.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[HotStab]

Mike,
It's not downhole. And it's not resident equipment that would have long-term operational periods. It's a tool that is submitted to maintenance before each use.
I don't think that spiral failure should be a concern just because of a 0.060" wider groove for a static application. This is that I meant.