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





discolouration is observed on heat exchanger tubes. What could be the adverse effect on the tubes?

RE: discolouration

Maybe none. Color is often indicative of the temperature seen by the tube and comes from the formation of a thin oxide passive film - the thickness of the surface film forms the color you see and is generally a function of highest temperature the tube saw.

RE: discolouration


is generally a function of highest temperature the tube saw

shouldnt that read '...a function of highest temperature the tube saw, in combination with the medium'?

RE: discolouration

What is the material of the tubes. Are the tubes new or have they been in service and if in service what is the service medium?

RE: discolouration

XL83NL is correct. I held back because there has to be enough time at highest temperature for the film to grow and passivate, so the tube could have seen a higher temperature than the color indicates but only for a brief time. I never really thought about how the discoloration would differ in different mediums (I just assumed it would be the same for any oxygen-bearing medium). Do you have a reference on the subject?

RE: discolouration

The oxygen-bearing medium is what XL83NL is referring to, according to me.
If it happened in an inert atmosphere, there would be no discoloration, no matter how high the temperature went.

RE: discolouration

There's no context here.
What are the materials?
What is the environment?
Is the discolouration due to corrosion or deposits?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

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! Already a Member? Login


White Paper - The Evolving Landscape of Commercial Battery-Powered Trucks
What’s driving the evolving landscape of truck electrification? What are the barriers, motivators and strategies for accelerating the electric transition? What insights and resources are available for today’s design engineers working to achieve industry disruption and evolution? For answers to these and other pertinent questions, read this white paper. Download Now
eBook - Rethink Your PLM
A lot has changed since the 90s. You don't surf the Web using dial-up anymore, so why are you still using a legacy PLM solution that's blocking your ability to innovate? To develop and launch products today, you need a flexible, cloud-based PLM, not a solution that's stuck in the past. Download Now

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