What's the material of the separator? Ideally bolting material should be identical with that of the vessel.

DHURJATI SEN

Be aware that the HDG coating on the internal parts maybe cause a process contamination issue in operation.

Bolting what material to what material? HDG will have no chance in the acidic environment.

Steve Jones
Corrosion Management Consultant

www.linkedin.com/in/drstevejones

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

Be prepared to spend some money .......

The high potential for costly stainless steel bolting failure in a chloride rich environment has been explored before by learned people with degrees

Do some reading on the API/ASTM development of a comparitive ASTM pREN number and the testing for various stainless steels:

https://en.wikipedia.org/wiki/Pitting_resistance_e....

An excerpt from a Draft API Documentation API TECHNICAL REPORT 21TR1 "Materials Selection for Bolting:...
(Not a complete document but a good place to start, IMHO)


http://ballots.api.org/ecs/sc21/ballots/docs/21TR1...

"In order to prevent pitting/crevice corrosion bolting material selection for the intended service is extremely important. For seawater applications, industry standards recommend CRA bolting material with high Pitting-Resistance Equivalent Number (PREN). The PREN is based upon the proportions of the elements
such as Chromium (Cr), Molybdenum (Mo), Tungsten (W) and Nitrogen (N) in the chemical composition of the alloy. The higher the PREN number the higher the resistance of the CRA material to pitting and localized corrosion. Alloys with PREN greater than 40 have demonstrated adequate resistance to localized
corrosion. .......Bolting can potentially fail when severe pitting occurs. In order to prevent pitting, proper material selection for the intended service is paramount; in seawater applications, austenitic stainless steels and stainless with a PREN greater than 40 have demonstrated to have good pitting resistance (amongst other materials)

Look at table #3 at the end of the API draft document ....

Be aware that seawater varies in chlorides but around the world 35,000 is a good rough average

I believe that the NORSOK standards (if you can find them) contain authoritative and definitive recommendations for various stainless materials in different types of seawater service. They specifically address

Like the CHEVRON, EXXON and others, the excellent NORSOK standards have been systematically ruined and eliminated by the human excrement and corrupt "Third World" internet organizations trying to make a quick buck by stealing the hard work of others... e.g.

https://www.scribd.com/document/299379327/NORSOK-S...

Respect us Geezers .... Let us know of your final material selection decision


MJCronin
Sr. Process Engineer

Based on this document,

https://www.csidesigns.com/uploads/resources/SSS-G...

Suggest that you consider:

ALLOY and pREN

AL-6XN 42.7
Alloy 625 46.4
Alloy C-276 73.9
SEA-CURE Stainless 49.5

Be aware that not all of these materials may be offered in a bolting configuration.

My guess is that, that venerable old "bad boy" C276 will be the cheapest

How many of these bolts do you need anyway ?

MJC

MJCronin
Sr. Process Engineer

Thanks all,

The material of the separator is SA-516 70 coated with 100% solids epoxy, and the bolting will be used to joint internal SA-105 flanges coated with the same paint. The quantity of stud bolts is about 150.

The final selection has been A-193 B7 HDG (I alerted the risk of failure due to high attack in the galvanic coat and I recommended the Alloy 625 or C-276 based on the MJC post and the NORSOK standard but unfortunately the final decision was not mine).

I have seen this done 2 ways, use C276 and forget about them, or use coated steel and require monthly inspections.
Do they have a required inspection schedule?
Remind them that once these start to corrode they may only last a week or two.

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P.E. Metallurgy, consulting work welcomed

Thank you EdStainless,

No, our client does not specify inspection schedule, but I will point to that.