SA312-TP316L

[GemmellG]

Working on LNG piping system (Cryogenic). Received pipe spools from another vendor upon inspection it was noted the piping had really bad deposits on the internal surface of the piping. It was decided to remove the deposits by light grit blasting which was very successful. Please note the blast medium has 10% to 20% iron oxide. Piping system installation is in two phases. Phase one is to install the main pipe runs & end cap & put system under nitrogen purge for approximately 12 to 14 months. Second phase is to complete final tie-ins to auxiliary equipment after all of the final tie-ins are complete the complete piping system will be flushed & passivated @ this time. My question is can the first phase of installation be passivated at the completion of phase two.

 

[metengr]

Yes.

 

[GemmellG]

Metengr thanks for the quick response.

 

[EdStainless]

Yes, but it may take a lot longer. If you have allowed surface deposits to rust (during fabrication) then you will find yourself circulating acid longer before the Fe levels stabilize.
Passiviating components as you go may sound redundant, but it will make the final cleaning much easier.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

The OP stated

Phase one is to install the main pipe runs & end cap & put system under nitrogen purge for approximately 12 to 14 months

. Under a proper nitrogen purge there should be minimal issues with corrosion when Phase 2 begins.

 

[georgeverghese]

Off hand, I would reject these piping spools, assuming the corrosion mechanism is part chloride induced SCC and part chloride pitting corrosion - it is the SCC mechanism that would be the justification for this rejection.

 

[GemmellG]

The rejected internal surface was plasma spatter there has been no chlorides introduced to the best of my knowledge.

 

[EdStainless]

metengr, I read the nitrogen purge comment, but the time that parts sit in the yard, and the time it takes to finish erection mean that it could be months before the system is put under purge. So for parts that they know have issues with surface cleanliness it would make sense to passivate at installation.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

One other consideration of Ed's recommendation is that most LNG plants being constructed today are located in a marine environment with salt ocean spray and windblown particulates which can exacerbate a potential corrosion problem.

 

[GemmellG]

We have a four week window to complete the field installation (first phase). All shop assembly will be complete in our stainless shop & preserved accordingly for shipping to site. Pipe spools will have Minimal exposure to the salt water environnement. I really appreciate the top notch discussion on this matter. Thanks

 

[metengr]

Thanks for the follow-up. No issues.