Buckling of spiral wound gasket with graphite filler 3

[arunb]

Hi everyone,
I am looking to substitute EPT rubber gasket with SS304 spiral wound gasket (with 99.5% graphite filling) on all piping flanged connections. I have read that there are quite a few cases of buckling of the metal winding and then finding their way into the piping. I was looking for some oprtational feedback or information on failures of this type. I am not sure if I should specify inner ring for these spiral wound graphite filled gaskets.
All feedback welcome.
Regards

 

[unclesyd]

Add the inner ring and you have the spirals trapped. All the "buckling" failures I'm aware of were on spiral wound gaskets without the inner ring.

Our gasket specifications for spiral wound gaskets all call out an inner ring, except for a very few specials.

Make sure you have proper flange and bolting to properly seat the spiral wound gasket and if the material compatibility is correct you can count on achieving a high integrity joint.

 

[arunb]

Thanks for the information which certainly was helpful. However would like a clarification whether the inner ring is recommended for graphite fillers or is it used across the board for all fillers.

 

[bingopin]

Inner ring is the way to go. A Flexitallic designation is "CGI" with the "I" standing for the inner ring. We have evolved to using inner ring gaskets almost exclusively where originally we would only apply them at the inlet flanges to special purpose machinery, such as large steam turbines.

I have also seen issues with large bore slip-on flange applications. Since the bore of a slip on flange is ~ 2 pipe wall thicknesses more than the bore of a weld neck, for a given flange size there is less area on the id of the gasket surface. While our particular case did not lead to the gasket unwinding, it did cause leaks. Our fix was a custom sized inner ring gasket.

 

[unclesyd]

We use the inner ring on all spiral wound gaskets regardless of the filler we use, mainly graphite and mica.

Long before spiral wound gaskets were widely used in process applications we required inner rings in our polymer system to eliminate the dead space on the flange faces.

Anecdotal:
Saved by the inner ring. In our nitric acid plant we have a large hot gas line operating at 250 psig @ 1250°F moving gas to the high pressure expander. There are 2 flanges in the line used to allow removing a cone strainer at the turbine inlet. The specs for this line call for ceramic filled Inconel gaskets with an inner ring. During slow roll after an overhaul a loud noise was heard near the strainer. Taking no chances the strainer was pulled and the night crew grabbed two new gaskets and reinstalled the strainer. After a 120 day run I was standing near the expander while the strainer was removed. Both gaskets had no filler only inner ring and spirals. I checked the stamp on the gasket and it said graphite. The graphite had oxidized and the spirals held in by the inner ring had held for the duration of the run. Without the inner ring the spirals would have unwound and ended up passing through the expander.

 

[gasketguru]

The ASME B 16.20 standard requires the use of inner rings for all PTFE filled and for other materials at over 24” in class 900, 12” in class 1500 and over 4” in class 2500 to help support the inner ring and prevent buckling. The use of inner rings across the board is generally a good thing.

You may be thinking of a well reported problem a few years ago, where a number of 16.20 standard gaskets suffered inner ring buckling, because the inner rings were just too narrow. (Gaskets made to BS 3381 sizes did not suffer the same problem.) There were revisions of the ASME 16.20 in 1998 and 2000 to make the inner rings wider on a number of the worst case sizes.

In terms of slip-on flanges, then consult your supplier regarding small sizes (1½” and below) as this is where there are often problems regarding the sealing element I/D.

In many instances, a number of users are now substituting kammprofile gaskets instead of spirals as they are generally more robust and cannot come unwound or spring apart during handling.

 

[unclesyd]

Looking at your original post something that should have I should have earlier earlier is your mention of switching from EPT rubber to a spiral wound gasket.

You will have to make sure you have enough flange to properly seat the spiral wound gaskets. Generally it takes a Class 300 to achieve this without any special considerations. If you have Class 150 look especially careful at the 3" and 8" sizes.

 

[NozzleTwister]

Lamons Gasket Company recently conducted a Lunch-n-learn at my company. I was very impressed with the Senior Applications Engineer that presented the program. They covered when you need or don't need an inner ring. I think they said the biggest problem with sending the windings down the pipe was when the gasket inside diameter projected into the pipe opening. The wrong gasket in the wrong place. I would give them a call and ask to talk to an applications about specific technical problems. They're in Houston, Texas.

Lamons Gasket Company
1-800-231-6906

NozzleTwister
Houston, Texas

 

[arunb]

Regarding switching from rubber to spiral wound gasket, the spiral wound gasket is about 0.1" thicker than the rubber gasket in the compressed position.I have asked for an assessment of the piping to be done viz. flexibility and stresses to determine if it appropriate to make the change.
We use standard ANSI B16.5 flanges. I am not sure if there is any concern regarding the flanges themselves.

 

[LSThill]

Team Members & NozzleTwister Houston, Texas

Technical Link

Lamons Gasket Company
1-800-231-6906

http://www.lamonsgasket.com/