×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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!

*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

PWHT and Ferrite number

PWHT and Ferrite number

PWHT and Ferrite number

(OP)
Hello,

According to API RP 582, the ferrite test should be performed prior to PWHT. But, I was reading a research article where it was shown that a large percentage of delta ferrite desolves during PWHT (in the research findings it went down from 8% to 1.2%) if the PWHT temperature range is 950 - 1050 °C. I am talking about 304H here. So, to me it seems that if I am performing PWHT in this temperature range, I should logically perform ferrite test after PWHT, as my concern should be the ferrite remaining in the final structure.

Why then is the API code insisting on perfroming ferrite test before PWHT?

RE: PWHT and Ferrite number

I see both required. The one after weld is part of the weld process QA, the one after is to confirm response.
In a true solution anneal the delta ferrite should drop below 0.5%.
Why that temp range?
The lower end is still in the stabilization range and the upper end is nearly a solution anneal. You will get very different response (and properties) at 950 vs 1050.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: PWHT and Ferrite number

(OP)
You are right, I will refine my question. The client has asked to perfrom 960° for 90 minutes. I found in literature the graph attached. PWHT at 1050 for 4 hours reduces it to 1.2%. Interpolating from the graph, PWHT at 960° for 90 minutes the reduction should be to around 4.7%.

But in any case since the total ferrite content is reducing after PWHT what is the point of ferrite test before PWHT?

And what is the remedy in case before PWHT the ferrite number is higher than expected? Refusal of component? Or modification of PWHT?

RE: PWHT and Ferrite number

In case before PWHT the ferrite number is higher than expected? Refuse the component, becouse is an exigence of the sepec.

luis

RE: PWHT and Ferrite number

You need to check before to make sure that the weld procedure was followed.
If you are expecting to hit some value after there is a big difference between starting at 6 vs 12 FN.
960C is not and anneal, it is too low especially for an "H" alloy.
If the intention is to re-anneal you need 1020C or so in order to get it done.
Did the paper that you got the figure from have any micros in it? Did they talk about the changes in carbide size and distribution?
Strictly speaking reduction in delta ferrite is a side effect of annealing SS, you are really trying to eliminate grain boundary carbides. The problem isn't the carbides but the fact that the Cr in them has been sucked from the material along the boundaries leaving these areas depleted in Cr and with much lower corrosion resistance. This is the sensitization that people talk about.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: PWHT and Ferrite number

Ferrite, a small amount, is desirable during welding to mitigate the potential for solidification cracking.

Performing a PWHT at the higher temperatures, cited in another response, would as permit the chromium carbides to dissolve and go back into solution thereby eliminating sensitization and mitigate the potential for intergranular stress corrosion and intergranular stress corrosion cracking.

At least that’s what I read in a book once upon a time.

Best regards - Al

RE: PWHT and Ferrite number

What is the equipment and why are welds being annealed?

Ferrite in austenitic fillers is only needed to avoid hot cracking; after that we usually don't care, although ferrite cannot be tolerated at all in some corrosive environments.

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

RE: PWHT and Ferrite number

It also cannot be tolerated in high field magnetic applications.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

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


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. 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