Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here





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.

RE: SA312-TP316L


RE: SA312-TP316L

Metengr thanks for the quick response.

RE: SA312-TP316L

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.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: SA312-TP316L

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.

RE: SA312-TP316L

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.

RE: SA312-TP316L

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

RE: SA312-TP316L

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.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: SA312-TP316L

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.

RE: SA312-TP316L

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

RE: SA312-TP316L

Thanks for the follow-up. No issues.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close