Gasket for GI pipe 1

[nickypaliwal]

Client is using SPW (SS316+Graphite) gasket for connecting galvanized CS flanges.

Although the service is instrument/utility air so temperature may not go high, I am doubtful about it.

is above combination acceptable?

What alternative do we have if the flanges are raised face and insulation kits are costly?

Also comment if service is potable water.

 

[moltenmetal]

A composition gasket such as this is what we use instead: gets rid of the galvanic corrosion issues entirely, is cheap, and lasts substantially forever in instrument air service:

https://www.garlock.com/en/products/blue-gard-style-3000

The website shows a flat face gasket, but ring gaskets (without stud holes) are available, cheaper and a better choice for raised face flanges.

 

[nickypaliwal]

Thanks for the alternate option. However please also present your views on SS316 SPW gasket.

 

[EdStainless]

Both the 316 and the graphite are very noble compared to the steel. If a conductive fluid is present then accelerated galvanic attack of the steel flanges would be expected.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

The spiral wound gasket is 10x as expensive as the alternative I gave you, and will not cause galvanic corrosion. Why would you persist in using the spiral wound gasket?

 

[nickypaliwal]

Actually the SPW is preferred since it is time consuming to get client approval on a new gasket type.

Also I have 2 concerns/questions:
- The flanges that we are using are raise face weld neck flanges (already ordered) so not sure if NBR gasket can be used as it looks like a gasket for flat face. Please confirm.

- Since the issue with Galvanized Steel and SS316 is Liquid Metal Embrittlement and not precisely galvanic corrosion, SPW gasket should also not create issues unless high temperature is reached. If temperature is high then even the NBR gasket would fail.

Is stainless steel to galvanized coating contact any issue until the galvanized coating starts melting i.e. probably up to 250degC?

 

[moltenmetal]

OK, I've got to admit I'm getting a little bored doing your research for you, especially if you aren't going to read what I post thoroughly before I reply...

If you actually read my previous post, you'd know that you can buy composition gaskets for use with raised face rather than flat-face flanges. They're punched from sheet and can be made to whatever dimensions you need.

Composition gaskets aren't NBR gaskets- they're compressed fibre with NBR binder. Their properties are nothing like those of sheet NBR rubber.

If I'm not mistaken, you're the one who has a large threaded galvanized instrument air system which is leaking at the threaded joints. You have threaded flanges, not weld necks.

The issue with using a GRAPHITE-filled stainless steel spiral wound gasket IS galvanic corrosion. The reason the piping is galvanized is to provide protection against aqueous corrosion, and you're introducing a new cathode into the system (the graphite in your gasket) which will drive a galvanic current to eat your anode (the zinc on your pipe) leading to premature loss of protection. If you are operating hot, above 400 F, which you are not, then you will not be using galvanized pipe and you definitely will not be threading either. Liquid metal embrittlement is NOT an issue for you, unless you do something stupid like WELDING the galvanized pipe, which you were warned about on the other thread.

If corrosion isn't an issue, then you can use your spiral-wound gasket, as long as you choose one which has a bore of the correct diameter for use with threaded flanges. Threaded flanges have an ID which is larger than the ID of the pipe, so make sure your gasket has the correct bore or this will happen:

 

[nickypaliwal]

I am sorry for my ignorance on composition gasket which from the link looked like a flat face gasket although I saw raised face in your response so wanted to reconfirm.

We have both cases with threaded and flanged connections.

Anyways thanks for your answers as it resolves all the questions I asked.