ASTM A234 WP9 Cl.1 vs Cl.3 1

[Technopriest]

Please, I need help in understanding some points of ASTM material specifications.

On ASTM A234, several materials are listed including WP9 Cl.1 and WP Cl.3. Cl.3 has better strength (both UTS and Yeld).
On ASME B31.3 (2012) and ASME II part.D (2004) ASTM A234 is listed but Class/condition is empty - so it seems that different classes of the material are not considered in this case. From yeld / tensile strength it seems to me that the listed material matches Cl.1 conditions.
ASTM A234 do not differentiate P9 Cl.1 and Cl.3 for heat treatment or other conditions.

My questions are:
- I need A234 WP9 elbows for a refinery vacuum heater. I do not have specifications from customer. Which class of P9 should I specify in the order?
- What is the difference between the two classes of P9? Chemical composition is the same, so I expect the difference to be Thermal treatment, but where should I look to find which material is best suited for what application?

I thank you in advance for any help.
Sorry for bad english wording, I am not of english motherlanguage and I just try to manage..



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[metengr]

I need A234 WP9 elbows for a refinery vacuum heater. I do not have specifications from customer. Which class of P9 should I specify in the order?

WP9 CL1 is the most common.

What is the difference between the two classes of P9? Chemical composition is the same, so I expect the difference to be Thermal treatment, but where should I look to find which material is best suited for what application?

Heat treatment and chemical composition range to achive the higher strength level for CL3.