Shop: Protection for Stainless Work 2

What you ask for is familiar to many but very tedeous to repeat here. Try the SSINA website where there will be downloadable papers on this and other useful topics.

Michael McGuire

The short answer is "never let the stainless contact any surface or tool that is steel and prevent all dust/dirt containing carbon steel from landing on it".
In practice this is a hundred different little actions, and a lot of remediation to fix problems.

Read up some and then come back with specific concerns.

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Rust never sleeps
Neither should your protection

Try NiDI - they have lots of good stuff - here's a few:



NiDI #10004 - FABRICATION AND POST-FABRICATION CLEANUP OF STAINLESS STEELS (1986)
By Arthur H. Tuthill, reprinted from Chemical Engineering, Sep 29, 1986

Use brass hammers and wedges.

Carpet and rubbber to protect from forks on forklifts and rigging when lifting.

Be careful of all shears, brakes, and rolling equipment that has previously been used on carbon or that contains carbon

Code only applies to structural aspects of the design. If you are concerned about cleanliness and corrosion resistence then you need to place some supplemental requirements.
I have seen entire process units passivated and then tested for residual iron on the surfaces.
This really should me a minimum requirement. Even if the shop is careful they will get iron on the stainless. Good shop paractice will simply prevent it from being too bad.
Do you reall want horror stories?

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

Thanks for everyone's replies. I am new to the industry and just wondered where and how to learn more about standard practices and tried and true methods.

I don't want to sound pedantic, but the contact precautions should be gainst iron, not carbon. Carbon steel, cast iron, alloy steel are all the same interms of embedding of iron. Carbon is not the culprit.

Carbonaceous material will only hurt if the material is subsequently heat treated while contaminated.

Even iron contamination is mainly a esthetic problem, because it rusts and makess people think the stainless is rusting and therefore defective, which is why we passivate to remove it.

Michael McGuire

This issue goes a lot deeper than just damage to the surface passive film. Iron on the surface of stainless can act as the initiation point for crevice corrosion. As the iron rusts the corroison products form a deposit creating the crevice conditions. The corrosion products them self are an electrolyte that contains metal ions. This is often made worse by also traping other impurities like chlorides. This results in lower pH, breakdown of the passive film (that can't reform under the crevice) and pitting initiation.
If the deposite is large, like spatter from grinding or welding, then this all happens faster and worse.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

Thanks ED.

That is my understanding as well. Iron/carbon contamination causes pitting big time.

GG

I can tell you from repeated first hand experiences that if there was a lot of grit blasting and grinding going on at the yard location with stainless steel tubing getting contaminated, then we get tubing leaks on location when we start up operations. The other issues with stainless piping seem to be more esthetic than an actual starter for leaks.

This is an amazing thread, thank you all! A landfill gas pilot project has had two failures of a S/S bellows pump (the sales engineer has not been helpful in describing the composition of the stainless steel, other than to say it is not passivated). In one case corrosion appears to be the culprit. Hydrogen sulfide gas has been found at 25 ppm, which could be the main problem on corrosion. An in-line heat exchanger brings the relative humidity down prior to the bellows pump, but is only functional when operating, and there have been a number of start-stop cycles which might introduce condensation to the internals when cold. A critical meter is also S/S and may need protection, in addition to the new replacement bellows. I'd like to know whether passivation can be done after surface corrosion has already taken place, and whether it would be useful to pursue this approach.

Also, I am currently considering making an H2S gas removal subsystem, using DMEA, which seems better than NaOH for handling and overall effect on the S/S. Probably a small CCE packed-tower would handle it. Any thought or suggestions on this problem?

Dirk, please post your questions as a new topic. By asking a question within someone else's post, you are "highjacking" the thread.

If you post your question separately with a descriptive subject line, more people will likely read and respond to it.

Good luck!