hot dip galvanized bolts forbidden on Stainless Steel vessel? 4

[YuJie_PV]

Hi all experts,

we are implementing a project which locate alongside the sea. that means corrosion is serious.
recently, our corrosion engineer raise additional statement that "hot dip galvanized bolts are forbidden on Stainless Steel vessel", even the operating temperature is ambient.
the reason is that in case of fire, the zinc in HDG coating could cause LME(liquid metal embrittlement) of SS vessel. i've never heard of that before.
is it a common practice?
the project is completed for almost 50%, i don't like to introduce any new requirement.
and the project is not offshore, i think the risk of LME is overestimated.
any experience in this field?
Thanks in advance.

 

[Louisiana Inspector]

That's an interesting article. I have read theories and reports on PTFE fasteners being prone to self-loosening due to the nuts being oversized to make up the difference for the coating thickness.
At my site, we only use PTFE-coated fasteners and are a batch-production therefore the piping/equipment is in cyclic services. From experience, I have only witnessed a fastener coming loose from incorrect torquing due to poor craftsmanship.

 

[GGedge]

Not sure where the project is the OP refers to, but if Eurocodes are ruling standards note this clause from EC3 Design of Steel Structures.

A.5 Galvanizing and contact with molten zinc
(1) Hot-dip galvanizing of components made of stainless steel is not allowed because contact with molten
zinc can cause embrittlement of the stainless steel.
(2) Precautions should be taken to ensure that in the event of a fire, molten zinc from galvanised steel cannot
drip or run onto the stainless steel and cause embrittlement. Additionally, there is a risk of embrittlement
if a stainless steel component is joined to a carbon steel component which subsequently undergoes hot-dip
galvanizing.

Which is the Normative Annex A of EN1993-1-4 Supplementary rules for stainless steel.

Cheers

Graham Gedge

 

[ProSafPlant1]

Here's a summary of some zinc LME incident references I first did about 20 years ago.

retired, technical library for sale on eBay -

https://www.ebay.com/usr/prosafbooks

 

[YuJie_PV]

@SJones, @Louisiana Inspector,@GGedge, @ProSafPlant1
Thanks for all your replies.
there is something really broadening one's horizons.
@ProSafPlant1, thanks for your PPT, i am reading it, it's very inspiring.
you mention Flixborough disaster as well in the summary.
regarding the disaster, i find there are two hypothesis explaining the occurrence of the explosion online, Just out of curiosity, is such a conclusion without a determined truth uncommon in the investigation for a plant incident?

thanks.

 

[rscosta1976]

Fluoropolymer coated fasteners are being specified in several of our projects requiring high corrosion resistance at near shore or offshore areas. I'm not aware of any issues entailing fasteners coming loose, provided the required torque is applied.

Thank you Steve for sharing such an interesting article.

I would take the opportunity to ask about the utilization of Hot dip galvanized fasteners in carbon steel piping, provided that LME of SS is not a concern. Some SMEs state the HDG fasteners shall not be used at all in piping, as wrong/incorrect (higher than actual) torque readings can be obtained due to excessive friction - would lead to insufficient torqueing of flanged joints that could possibly lead to leaks. Your troughs would be appreciated on this matter.

Thanks

 

[WKTaylor]

Are You aware of related specs on this topic, thus...

MIL-HDBK-843 SHIP METALLIC MATERIAL COMPARISION

MIL-STD-889 GALVANIC COMPATIBILITY OF ELECTRICALLY CONDUCTIVE MATERIALS

SAE...
J2655 Fastener Part Standard - Washers and Lockwashers (Inch Dimensioned)
J2270 SHIP SYSTEMS AND EQUIPMENT - THREADED FASTENERS - INSPECTION, TEST, AND INSTALLATION GUIDANCE
J2271 SHIP SYSTEMS AND EQUIPMENT - PART STANDARD FOR STUDS - CONTINUOUS AND DOUBLE END (INCH)
J2280 SHIP SYSTEMS AND EQUIPMENT - FASTENERS - SELECTION AND IDENTIFICATION GUIDANCE
J2295 Fastener Part Standard - Cap Screws, Hex, Heavy Hex and Heavy Hex Structural Bolts, and Hex Nuts (Inch Dimensioned)

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rscosta1976]

Thank you WKTaylor

I'm indeed not aware of any of the standards/ RPs you pointed. I will check it out and try to learn something.

So do any of these actually prohibit HDG fasteners due to incorrect torque concerns?

Thank you

 

[WKTaylor]

Also... contact...

American Bureau of Shipping, ABS Plaza, 16855 Northcase Drive, Houston TX 77060 USA

The 'ABS' has a 'trove' of rules/data/specs for large ship building... and works hand-in-hand with the US Coast Guard.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov