MATERIAL MIX UP

[Uccio]

Dear All,
One of our supplier delivered A234 WP91 instead of A234 WP9 as per our order.
He thinks to be right saying that mechanical values are the same and that the heat treatment has been made according WP9.

This looks silly to me...

 

[stanweld]

Your supplier has not given you what you ordered; thus, you are within your rights to return it to the supplier for the correct material. WP91 mechanical values are greater than WP91, although much of WP9 Class 3 will be within the WP91 range. The PWHT requirements for WP91 are somewhat more restrictive than for WP9. The service conditions dictate whether you accept the substitute material.

 

[Uccio]

Thank you, but I would like to understand better the problems caused by welding togheter WP9 and WP91.
Asymmetric Vanadium content can create problems?

 

[metengr]

Grade 91 material is a creep strength enhanced ferritic steel that is actually much stronger (much higher allowable stresses) than the more common Grade 9 material. Yes, vanadium and other less obvious alloy additions result in higher elevated temperature strength and because of this different fabrication rules are necessary to provide controlled conditions for thermal treatment after fabrication (forming and welding).

As stanweld mentions you have the wrong material that was delivered and unless you understand the fabrication characteristics for this material, you can be placed in harms way. in other words using fabrication guidelines for Grade 9 cannot be used for Grade 91.

 

[stanweld]

Typo correction, "...WP91 mechanical values are greater than WP9..."

Agree with metengr; "...you can be placed in harms way."

 

[EdStainless]

If the design is not creep limited then you might consider using the part. Be warned that you will need to follow the welding and PWHT rules for 91 if you do.

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