Stainless steel Huck bolts - broken end corrosion

[trainguy]

Hi all,

We have always protected broken ends of Huck bolts with zinc-rich paint, when using C120 Grade 5 steel pins. It it a good idea to to the same with stainless steel C6? Or will the zinc-rich paint make it worse?

tg

 

[BridgeSmith]

I wouldn't think applying zinc-rich paint to stainless steel would do anything...except flake off later.

 

[MJCronin]

Its important to understand how galvanizing and zinc-rich paints protect carbon steel.

https://www.astm.org/SNEWS/APRIL_2006/dallynside_apr06.html

Remember, when carbon steel corrodes, it forms big flakes that fall away. Zinc protects against this corrosion. Stainless steel forms an oxide layer, but does not flake .....

It is a good idea to review the galvanic series ....

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

You could also post your question in the "Corrosion Engineering" forum and get a better answer

MJCronin
Sr. Process Engineer

 

[cap1a79]

Yes. Zinc on stainless steel could make it worse.
There is a mechanism of liquid metal embrittlement when stainless steel contacts with zinc and it is susceptible to brittle fracture especially in fire case. It is common practice to avoid any contact between the two as clearly described in section 4.5.5 and table 4-9 of API 571. )

(Quoted from API 571 section 4.5.5.6)
300 series SS should be protected to avoid contact with galvanized components and overspray from zinc and inorgarnic zinc coatings.)

(Unquoted)
If the bolt is just to open to air (NOT submerged nor internal bolt of process fluid), the use of bare stainless steel bolt will be O.K as oxide film as CR2O3 on ss can protect the surface from atmospheric corrosion.


Lee SiHyoung,
Engineer - Material & Corrosion Specialist
WorleyParsons Oman Engineering,
cap1a79@gmail.com

 

[EdStainless]

In general you are better off leaving the SS bare. If you coat it then you have formed a crevice corrosion situation, and every little holiday in the coating will be a corrosion initiation point.
If people have to provide galvanic protection for SS they prefer to use thermal spray Al and then cover it with a sealer.

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P.E. Metallurgy, Plymouth Tube