Gasket questions 3

[Mooonlight]

Hi all,

I recently started to work with maintenance at a refinery and I have a few thoghts and questions about gaskets.

1. Why does the outer ring of a spiral wound gasket (with inner and outer rings) sometimes get warped (like a satellite dish) when installed?
A manufacturer (not the same one who made the warped gaskets) told me that it had been wound too tight during manufacture... But I was thinking that perhaps it's more because the wound part needs to be compressed when installed, but it can't expand sideways because the inner and outer rings are stiff, so the outer ring gets deformed.
What do you think?

2. What type of glue is recommended to make a gasket with graphite tape stay in place during assembly of a heat exchanger? I have heard that most kinds of glue may cause problems with chlorides. And grease might make the gasket seal badly and might also damage the graphite when boiling/evaporating.
Is any of this true? What do you people use?

All ideas are greatly appreciated.

 

[dtn6770]

1) Improper handling.
2) Use just enough masking tape to keep them in place.

 

[SnTMan]

Mooonlight, for your second question, some use 3M 77 spray, most gasket makers recommend it. You could also use adhesive backed graphite tape, available from any gasket supplier to hold gaskets in place.

For your first question I tend to doubt the "wound too tight" explanation. Does this happen at install or after being placed in service? What sizes of gaskets are involved?

Regards,

Mike

 

[unclesyd]

The cupping of the outer ring has nothing to do with the spiral windings. The windings are cushioned by the filler.

Mechanical damage as you describe with spiral wound gaskets in normally caused by the gasket being a little too large and the threads of fastener picking the edge of the gasket. The gasket needs a 1/16" diametrical clearance to alleviate this problem.
One other cause, rare, is that the flange is cupping due to fastener overload or the wrong style of gasket for the application.

As far a graphite tape or HE gaskets we use a tack adhesive to temporary hold the material.

Be very careful with masking tape or especially cloth tape around gaskets use in high temperature service. Make sure no tape crosses the gasket in the radial direction.

 

[Mooonlight]

Thank you all for your replies!

SnTMan,
The outer ring of the gasket gets deformed during installation, that is before start-up. I've seen it in sizes around 10", but it is possible that it happens on smaller and larger gaskets too.

Unclesyd,
It is quite possible that the fasteners are in the way. I haven't thought about this possibility before.
Which tack adhesive do you use?

 

[unclesyd]

We mainly use the 3M 77 mentioned by SnTMan. There are several that will work and most supply house have one.

 

[SnTMan]

Mooonlight, if the outer rings are interfering with the bolting, either the gaskets are not properly made, or perhaps gaskets for different flange ratings are being substituted.

Flexitallic, for one, has dimensional charts for the various sizes and ratings for B16.5 flanges. You might get your hands on one if you don't already have it and check things out.

Regards,

Mike

 

[Mooonlight]

SnTMan,
Thanks. However, I am quite sure that we use correct gaskets, both size and rating. But, maybe a vary low percentage of gaskets might have slightly larger outer ring from manufacture? Or they may have got compressed a little too much? Another possibility is that the two flanges were not completely centered or that the gasket was installed slightly off center.

 

[unclesyd]

Over the years I have seen oversize gaskets from nearly every manufacturer.

In an emergency we have even send the gaskets to the sheet metal shop to punch segments on the periphery to accommodate the studs. For years the shop kept templates to accommodate all our major flanges.

 

[JJPellin]

I have seen the problem you describe in your first question many times. In almost all instances, the two flanges were somehow different. I have tended to see this problem at the first flange where a pipe connects to a piece of rotating equipment. As you note, I have seen it in cases where I am positive that the correct gasket was used. I have also seen it in cases where I am positive that there was no interference with the studs. However, since one of the two flange faces was "part" of the compressor or turbine, the dimension of the raised face may not have been identical. I believe it is a result of uneven forces on the two sides of the metal ring because the two flanges are not identical.

The first time I saw this I consulted with flange and gasket experts. One of them told me it was normal and not to worry about it. The other one told me it was a defective gasket and it must be replaced. I replaced the gasket with a new one from a different source and it did the same thing. Since then, I have seen it many times and have started listening to the first expert. I don't worry about it. I have never had a leak or any other problem from one of these cupped rings. I know of examples running in our plant today in 400 psi steam, 1400 psi hydrogen, high pressure water, etc. Just make certain you have the right gasket, the right studs and use a proper tightening method (tightening order and torque) and you should have no problems.


Johnny Pellin

 

[GregLamberson]

For the originally posted question #2 - it will depend on what your service is, whatever glue you use, you will want to make sure it will not contaminate the sealing surfaces of the flange. Also, check to see if the glue will vaporize at your operating temperatures. As was poitned out, check with the gasket manufacturers.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[unclesyd]

Look at the picture on this page. It looks like a spiral wound gasket has been deformed as described in your post. As posted above the amount of distortion is tolerable on a one time basis if you have the flange.

http://www.boltscience.com/pages/gasket.htm

 

[Boser]

The outer ring of the Flex style gaskets get distorted when they are torqued (or tightened). I've seen this many times due to over torque of the fastener or simply becasue the two flanges did not line up perfectly. It is also possible for the threads of a stud or bolt to catch.

Regards, Boser