Corrosion Ques - 304H & Galv Steel

[CharlieH]

We are installing (2) 12' sections of 304H SS pipe that need to be supported in a couple spots. These are outdoor applications at an oil refinery.

IN order to support the pipe, I will need to weld material on the pipe that will then rest on galvanized steel.

Any suggestions?

One application is a typical pipe shoe (1/4" plate welded in T shape that is then welded longitudinally to the pipe wall. The flat part of the T goes down (basically upside T) which gives you a flat surface. The flat surface of the T will be placed on nearby galvanized steel.

Considering the pipe is 304H, should I make the pipe shoe out of 304H also and then rest it on galvanized steel? (Galvanic corrosion issues?)

Or should I make the pipe shoe a different material? If so, this will then require me to weld a different material to the outside of the 304H pipe.

I just don't know which is the best approach and could use guidance from some experienced people in this field. If neither of these are desireable and you know of another consideration, please pass it along.

Thanks for your time,
Charlie

 

[EdStainless]

Why is the pipe 304H? Does it run that hot?
Are bolted connections out of the question?
Is this going to be wet or is it a coastal application?

Yes, at some location you will ge some corrosion, but since these are fairly heavy sections and will not wet all of the time I wouldn't be too concerned.

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[CharlieH]

This is a compressor exhaust pipe that has existed for 35 years as plain carbon steel. The pressure is very near atmospheric. We are replacing the existing exhuast silencer with a catalytic converter.

The unit is set to shut down at 1250 F. Nothing we are doing should increases the temperature, but the current engineer saw that the existing plain carbon steel pipe spec only goes to 750 F at 100 psig and felt it was not sufficient. The 304H pipe spec is rated for 1500 F, so they feel this is the correct choice.

We are using bolted flange connections to connect the pipe to the cat converter. The unit is out in the weather, in southeast Louisiana, but not in the marsh (saltwater). Instead it is along the Mississippi River (fresh water).

Would the skin temperature being so high be a factor in eliminating moisture that would be needed for galvanic corrosion?

THanks again,
Charlie