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

CN7M casting to Alloy 20 Pipe - 1-1/2" Sch 40: Welding Procedure

CN7M casting to Alloy 20 Pipe - 1-1/2" Sch 40: Welding Procedure

CN7M casting to Alloy 20 Pipe - 1-1/2" Sch 40: Welding Procedure

We have a weld procedure for P45 to P45 material that has worked fine, but recently had an issue with 1-1/2" socket weld fittings made from cast CN7M.

Some of the castings developed pinhole leaks near the welds in the heat affected zone.
Hydrotest, air test, visual, and dye penetrant examinations prior to welding found a few issues, but nothing seemed to correlate to the crack development.

A welder with experience on these materials increased preheat to 150°F and issue the issue seems to have been resolved.

Not being a welding engineer, I wanted to find out:
- Is elevated preheat recommended for all P45 materials?
- Or for CN7M castings in particular?


RE: CN7M casting to Alloy 20 Pipe - 1-1/2" Sch 40: Welding Procedure

I'm not overly familiar with american designations of these steels (and the sometimes small variations between the different designations), but in general, no, elevated heat should be avoided.
Did you encounter hot cracking or other defects/cracks? What filler? Depending on a.o. the Ni%, either ferrite number or heat input should be carefully predicted/applied.
Should be kept - very - clean before/during welding!

RE: CN7M casting to Alloy 20 Pipe - 1-1/2" Sch 40: Welding Procedure

I presume that cleanliness was not an issue here, though these alloys are very sensitive.
These alloys in general and a 0 FN, which makes them very susceptible to hot cracking.
A little pre-heat can help and it shouldn't be an issue with the metallurgy.
It is more common to address this with controls on the heat input, weld speed, inter-pass temp, and cooling rate.
Allowing stresses to build during welding nearly guarantees cracking.
Castings can be problematic because the microstructures can vary.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

RE: CN7M casting to Alloy 20 Pipe - 1-1/2" Sch 40: Welding Procedure

Did you gap the root of the socket joint as required by ASME?
EdS raises relevant points, to which I would add: was the casting sound to begin with?

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

RE: CN7M casting to Alloy 20 Pipe - 1-1/2" Sch 40: Welding Procedure

Thanks for the prompt replies - and apologies for not responding until now.

The customer of ours with the issue sent his GTAW WPS. It specifies ER320LR, F#45, A#N/A(non-ferrous) and .030 to 3/16 filler metal with a 60°F preheat temperature.
As I noted, I'm not a welding engineer, but in my limited experience it seemed off, starting with "non-ferrous".
Checked vendor data: F6 & A9. Confirmed with a copy of Section IX.

We had one of our shop welders visit - he observed #1 - they were welding it cold, with no preheat - January in New Jersey cold.
#2 they were laying the wire down hot and doing a single pass.
He worked with them and made some successful welds with 150° preheat and 300° max interpass in two passes.

I also did some internet searching and found good information in a publication by the Nickel Development Institute.
It notes that some cast grades "such as CN7M" are fully austentic (i.e. 0 FN as EdStainless pointed out) and goes on to state that special techniques may be needed to prevent microfissures next to the weld.
Pretty spot-on for what we saw - pinhole leaks after welding in the heat affected area.
And the end of that paragraph say "Techniques available are low interpass temperatures, low heat input and peening of the weld to relieve mechanical stresses." Our experienced welder doesn't know the metallurgy, but knew to start warm but don't get it too hot.

I'm getting someone to create a formal WPS for our shop.

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


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