×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Jobs

316L and DI Water Rusting

316L and DI Water Rusting

316L and DI Water Rusting

(OP)
Hello,
We have a 316L Tank with 140 deg DI water. We are heating the water with a strip heater bonded on the non-wetted side of the tank.
In the areas where the heaters are bonded, we are seeing some rust on the wetted side. The heaters are bonded with a heat sink compound.
The DI water does have localized boiling but this is common in our tanks.

Any thoughts of why this may be happening? Poor grade of 316L?

RE: 316L and DI Water Rusting

1.  The tank may not have been passivated properly when it was built.
2. is this tank open to air?  You may have excessive levels of CO2 driving down the pH and making it more aggressive.

Turn the heater down, boiling does not improve your heat transfer much.

I would suggest cleaning the rusted areas with pickling paste and then nitric acid passivating the entire tank.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: 316L and DI Water Rusting

I think Ed's #1 is the likely cause.

RE: 316L and DI Water Rusting

(OP)
Thanks Ed, yes it is open to air.

One other item I left out was they are electropolished. This has happened on some recent non-electropolished tanks as well. So I am inclined to think that the EP is a non-issue.

Why does the rust only appear around the heater regions? Does this speed up the oxidation process?

Maybe this rust is not really rust and "burn" from the heaters. Looks like rust as it is more brownish than blue heat discoloration.

RE: 316L and DI Water Rusting

Just because they are EP does not mean that they were properly cleaned.  Does your spec prohibit the buffing of the tank? Do you require a nitric acid passivation after EP?
You should on both counts.
Turn the power down.  Once water starts to boil you probably are loosing heat transfer capacity.  The surface can get very hot since the steam formed does not transfer much heat.
While passivation is the most likely issue I still question the water quality.  When you boil you will get localized concentration of impurities.
What is your conductivity (total)?  pH?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

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!


Resources