316L gasket failure 4

[CREAAM]

I have an issue with a leak at the mid water flange of a 12” production line the corrosion of the gasket is considered a possible failure mechanism, since, the gasket material is 316L and the ring groove, flange face and bore are Inconel 625 clad. I am looking to ascertain the suitability of the gasket materials for the service conditions.

 

[Metalguy]

What kind and temp. of the water? Cl- level? Continuous or intermittent flow?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[CREAAM]

The process is multiphase produced fluids from a subsea manifold to an FPSO. The seawater is external, North seabed conditions:
Temp should range from about 6 to 17 °C and the Cl content should be 19345 ppm.

 

[EdStainless]

Probably not a good combination, the 316 is very marginal under those conditions, and being coupled to a more noble metal will accelerate the corrosion rates.

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Plymouth Tube

 

[TVP]

DEFINITELY not a good combination, especially if the expected lifetime of this gasket is more than a few weeks or months. Type 316L is just not suitable for fully immersed seawater.

 

[NickClark]

I'm assuming you have cp of the pipeline? If so then corrosion is most likely from the process not the seawater. But like the others say 316 not generally a good choice. I'm no pipeline engineer but I thought 316 gaskets were for test purposes only?

 

[SJones]

825 is usually the minimum considered for gaskets when the sealing surfaces are CRA. For wet made joints, 625 is usually the option. Review EEMUA 194, subclause 9.4. Since it would appear that the cause of the leak has not yet been identified, and we do not know the detailed exposure conditions of the gasket, it is not yet possible to speculate as to the suitability of the 316L.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[strider6]

"Metal to metal seals that may be exposed to sea water without cathodic protection should be made in corrosion resistant alloys such as UNS R30035, R30003, Alloy 625 and Alloy C276. Generally, metal to
metal sealing materials shall be more corrosion resistant than surrounding surfaces."[NORSOK M001


Corrosion Prevention & Control

 

[stanweld]

There is nothing worse than sandwiching a material highly susceptible crevice corrosion (316L) to much more noble materials (625). 316L will surely become like swiss cheese in your application. A similar 316 application was specified on the attitude control rocket valves on the Space Shuttle with predictable results. I changed it.