Pressure transmitter with diaphragm seal for very high salinity application

[Steve010]

I have to use a pressure transmitter with a flanged (Raised Face rating 600#) diaphragm seal on a the on the outlet of a well. The material engineer specified that the wetted parts shall be Hastelloy-C, so i chose the diaphragm material to be hastelloy-C. What should the diaphragm seal flange material be? should it be Hastelloy-C as well ? or is it ok to use a carbon steel flange, and rely on the gaskets to make the process fluid does not contact the flange ?

Also note that i can not use 316 SS flange because this will lead me to increasing the rating to 900# instead of 600#, as piping is working at the edge of rating 600# for carbon steel.

With regards to carbon steel, i am worrying about galvanic corrosion between the seal carbon steel flange and the hastelloy-C flush ring.
What do you think ?

 

[micalbrch]

Why not use a rubber lined/coated carbon steel flange? That would be my first choice. Definitely you need to select a suitable material for the diaphragm flange. Do not rely on the gasket only! WIKA offers even coated pressure transmitters. Not sure if they are cheaper than Hastelloy-C ones but it might be worth to check.

 

[Steve010]

Thank you very much micalbrch for your reply.

In general, is it a standard solution to use a rubber coated diaphragm seal flange or a hastelloy-c flange? most catalogues like emerson specify hastelloy-c for their diaphragm and 316 SS or CS for the flanges. why would some one select CS or 316 SS flanges with hastelloy-c seal if the process fluid requires the use of hastelloy-c wetted parts ?

 

[micalbrch]

I cannot answer that question but carbon steel or stainless steel are not an option for your application as far as I understand it. So, you must either go with Hastelloy-C or find an alternative. To use carbon steel or stainless steel without any protection and just rely on the gasket sounds a bit strange for me.