Spiral Wound Gasket Compression 1

[engpes]

I have an existing 2" 150# RF spiral wound flex gasket that has been in service for a while. We suspect that the initial torquing of the bolts may have been over torqued and the gasket may have been over compressed.

The gasket is functioning properly in service and not leaking.

My questions are:

1.). Is it really possible to permanently damage / crush a spiral wound gasket by over torquing the flange studs is it is a CG or CGI style gasket?

2.). Wouldn't the outer or inner ring prevent over compression of the gasket and act as a compression stop?

3.). The seating stress for this gasket is 10,000 psi (y value). Is there a max allowable compression stress for a 2" 150# spiral wound gasket? Or do the inner and outer rings prevent this?

PS - I am not concerned with bolting stresses here, only the gasket crushing force. Thanks in advance.

 

[TGS4]

The outer ring(and inner ring, if it exists) indeed act as compression stops. There is some debate about whether or not these gaskets actually also seal on the outer ring. If it's not leaking, I wouldn't be concerned.

 

[engpes]

So the way I see it, crushing a spiral wound gasket with an inner or outer ring is really not possible?

The flanges would bottom out on the rings?

 

[TGS4]

Yup

 

[racookpe1978]

Well, you will crush it past the the intended design point of the tiny flexible spiraled chevrons inside the gasket. If they are crushed tight against the two flange faces they "may not" leak but are squished against each other and twisted inside the remaining volume between the two rings - but NO manufacturer is going to give you any assurance that they will not keep tight after a change (heatup, shutdown, vibration, shock, water hammer, or earthquake or ice strom) on that assumption! If they are not leaking now, let them be as-is, keep checking weekly or monthly, and flag the joint to be opened, cleaned, inspected (no gouges!) and rebuilt with a new gasket at the next outage.

 

[granQC]

Hello!
In my opinion, there points that need to be clarified:
I) What criteria/aspect/visible identity in the flange connection that suspects you that it was overtorqued/gasket overcompressed?
Please also consider: a)What do you mean by crushed/damage and comparing it to compressed gasket? b) For over torqueing, meaning, torque applied is exceeding the gasket manufacturer torque value recommendation-how would you know?
II) I don't agree that you should not be concerned on the bolt stress since it will be inevitable, because the bolt stress is one of the design basis on the capacity of gasket compression/seating ~ tightening/torque.

But to answer your question, as per my understanding,
1) Depending on the point I clarification
2) Yes, it is one of its purpose however it only "limits" compression and not prevent "over" compression.
3) Limit is on Bolt stress/load-related also to operating/line condition

Ciao!