Chloride Stress Corrosion - Pressure Safety Valves 1

[valvepuke]

I have a philosophical discussion going concerning acceptable materials for pressure safety valves used in seawater. Our specifications require ALL Monel materials for the valves. These safety valves are low pressure units (ANSI Class 150, relief pressure 180 psig, 90 degF). The reason the specifications call for all Monel construction is to prevent chloride stress corrosion. I would like to utilize PSV's with carbon steel body and bonnet with all-monel wetted internals. My thought is that under normal conditions, the Monel parts are the only components in contact with the seawater. Only if the PSV blows due to overpressure will the carbon steel components contact seawater. This situation would be very intermittent (maybe never) and when PSV's blow they require attention anyway. The stress is low on the cast (ASTM A216 WSB) carbon steel, as far as I can judge. I realize that this approach is a compromise but the cost and time to delivery could justify it.

Please let me know what the big world thinks about this.

 

[Patinina]

Hi
You may go to check out NACE RP-0475 which reffres to High Chlorides services with Cl > 90000ppm.

There you will find the answer.
If you will try to buy from NACE by phone is better.
You will get the pdf format fast maybe same day.

Pat

 

[strider6]

sorry but you said that the materials are Monel and Carbon Steel, why you are concerned with Chloride Stress Corrosion?
Chloride Stress Corrosion is not a problem for Carbon Steel but for Stainless Steel.

http://www.corrosionist.com/Corrosion_Type_Stress_Corrosion_Cracking.htm

http://resource.npl.co.uk/docs/scie...ides/pdf/stress_corrosion_cracking_basics.pdf

http://resource.npl.co.uk/docs/scie...als/publications/online_guides/pdf/stress.pdf

S

Corrosion Prevention & Corrosion Control

 

[Patinina]

You are right, is the best for chlorides.
Monell construction is OK on this service, however check wih this stanadard NACE RP-0475 which is only for high chlorides services designed.
You have to stay awy far away from SS.

 

[MJCronin]

Valve....

Is it possible for you to use a rupture disc/Relief valve combinaton..?

The rupture disc can be made from a premium material 9titanium..?) and the relief valve can be made from less expensive materials.

The disc, of course, must be replaced after actuation and the valve would require cleaning.

-MJC