What¦s the best metalic coating for bolts in H2S environment? 3

[decco]

Anyone knows something about metalic coating for bolts used in H2S environment (Oil industry)? We are using Ni-Zn coating but I have heard something about brittleness by H2S in these bolts. All bolts we are using have embrittlement-relief heat-treatment. Is it possible some reaction between H2S and Ni-Zn coating?

Thanks in advance!!

 

[CoryPad]

Can you describe the joint(s) in more detail? What is the purpose of the metallic coating? To prevent atmospheric corrosion, to prevent acidic corrosion from a H₂S-containing fluid, other?

 

[TVP]

Yes, H₂S reacts with Ni & Zn and will result in the liberation of H. However, exposed bolting in sour service applications has certain requirements as specified in NACE MR0175 or ISO 15156, namely that the bolts should be Grade B7M according to ASTM A 193 with a maximum hardness of 22 HRC. In this condition, bolting will be quite resistant to EAC/HISC. What is the composition and heat treating history of your bolts? Strength/hardness?

 

[SJones]

Can we clarify the application? Are the coated items immersed in the fluid or are they externally located and are they to comply with ISO 15156?

Steve Jones
Materials & Corrosion Engineer

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

 

[decco]

Thanks for all reply! So, I´m looking for more information about the bolt specification.

- The coating is to prevent atmospheric corrosion;
- The bolts is not used immersed in any fluid, but in case of little leakage, could be subject to H2S atmosphere.
- The vessel/compressor that use the bolt works with some quantity of H2S.

Thank you in advance!

 

[CoryPad]

Does the coating need to be metallic? A PTFE-based coating appears to be a suitable option.

 

[SJones]

Now I'm lost. We've moved from the performance of Ni-Zn coating in H2S to 'information about the bolt specification'.

For atmospheric corrosion protection of bolting consult these two documents:

DNV Report 2002-3301 Bolting & Fastener Application In The Offshore & Process Industry - State Of The Art

NACE Publication 02107 Coatings For Protection Of Threaded Fasteners Used With Structural Steel, Piping And Equipment

Not sure that I see 'Ni-Zn'!

Steve Jones
Materials & Corrosion Engineer

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

 

[TVP]

Steve, thanks for the NACE reference-- I had not previously seen that.

 

[decco]

Steve, I guess I made a misunderstood in the last message... The subject continue the same! Ni-Zn versus H2S...

So, the spec of the bolts we are using is Ni-Zn with all treatment to avoid any problem related to H2S and H2 (ASTM A193 Gr B7M). All bolts are used externally in equipment that works with H2 and H2S, and after some operation time the bolts presents embrittlement. So, the spec is ok but probably the fabrication of the bolts was made without careful with the specified treatment.

I'm still researching...

Thank you all for the help!