Bolting for Duplex Stainless Steel Flange 2

[Xeros]

Hi,

Generally, I applied B8 (SS304) bolting for duplex stainless steel flange bolting. I think that this has no problem.

However,
I think that B8 bolting is not suitable if the bolting is in the environment that Chloride Stress Corrosion Cracking could occur.

Someone recommended to use B7 (1.0Cr-0.5Mo) bolting.

However,
In my opinion,
Application for B7 bolting could cause galvanic corrosion between low alloy steel and duplex stainless steel.

Is it right?

what is the solution for this problem if it was right?

At this point of time, it is difficult to apply the isolated kit for bolting.

 

[strider6]

SS 304 can crack (CSCC) in an atmosphere with high chloride (eg marine atmosphere)
The suggestion of Cr-Mo bolts is correct provided they are hot dip galvanized.
If if you look in Norsok specification for piping, L 001, they specify STUD BOLT C/W NUTS A193 B7/A194 2H
with Surface protection, "All low alloyed steel bolts, nuts and washers shall be hot dipped galvanized according to ASTM A 153."

http://www.standard.no/imaker.exe?id=1355

hope this help

S.

http://www.corrosionist.com

 

[EdStainless]

If you are really concerned you should use duplex or Ni alloy bolts. Yes they are expensive and a pain, but they will do the job right.

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Plymouth Tube

 

[CoryPad]

strider6,

I don't understand how hot-dipped galvanized low alloy steel bolts are expected to provide long service life when in contact with high chromium content steels in a marine environment. Are they supposed to be replaced at regular intervals?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TVP]

As EdStainless mentioned, duplex stainless steel fasteners are available that have high strength and immunity from SCC. Bufab Stainless (formerly Bulten) offers a number of duplex and super-austenitic grades that are suitable for marine use:

http://www.fera.org.uk/pdf/Fera seminar 2 Feb 06 - Soren Andersson - Bulten.pdf

http://www.bufab-stainless.se/eng/teknisk_1.htm

 

[Riadsala]

Careful if considering nickel 718 to ensure it is in accordance with API 6A718 and that they are not over-torqued, and that the hardness is 100% checked to be below 35 HRc, otherwise they could crack if there is any CP near...

Z100 super duplex would work also and is commonly used for bolting.

Riadsala
Metallurgist in the Offshore O&G industry