Carbon Content in P11 fittings

[pipe15]

The carbon content in A234 WP11 and A182 F11 looks like it can either be 0.20% max or 0.15% max.

a fabricator has stated... "if the design does not dictate the need for the higher carbon content, it would be wise to select the 0.15% max since this level does not require PWHT while the .2% does"

it there a reason I would need the extra carbon. The A335 P11 pipe has a max of 0.15%.

thanks
mark

 

[StevenHPerry]

You're talking of the different classes of WP11 and F11. These were recently revised/added by ASTM and now appear in B31.1 at least.

For A182 F11, Class 1 (the low carbon variety) matches your A335 P11 pipe as you say.

Class 3 (high carbon) has higher yield, ultimate, and allowable design stresses.

Why would you need Class 3? It would have to be a rare situation, but consider a forged valve. It could be the limiting component in the pipe spec. Bump it up to Class 3 and now you've bought yourself some extra pressure, assuming you can talk the manufacturer into it. Last I checked, the low carbon varieties hadn't made their way into B16.34.

Also, the fabricators statement is not entirely true. Read your applicable code and all the notes.

In my mind, it's safer to state that "PWHT is required except..." rather than "PWHT is not required unless..."

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[pingmi]

Steve,

I thought requirements of PWHT are goverened by following:-

Material P-Numbers (and not their carbon contents)
wall thickness
Applicable codes

Can ypu pls confirm or comment.

Thanks.

 

[Mr168]

That is a very dangerous assumption to make, and you must examine the PWHT requirements for every material you're using, for each applicable code.

There are a number of requirements based on the applicable codes for PWHT exemptions. In B31.1 for example, for P4 materials, you are restricted to a carbon content of 0.15% or less. There are also limitations on throat thickness for fillet welds, hydrogen content of electrodes, seal welds, etc.

 

[StevenHPerry]

pingmi, the applicable codes do govern! B31.1 has different requirements depending on P number and thickness like you suggest, but also carbon content and other items. Like I said, read your code and all the notes!

Mr168, I assume you meant my assumption about defaulting to PWHT required? My explanation was incomplete. Knowing the situation that we have a P4 material, we're undecided on carbon content, and we have no clue what thickness we're talking about, I would have worded the fabricator's sentence differently:

if the design does not dictate the need for the higher carbon content, it would be wise to select the 0.15% max since this level does not require PWHT while the .2% does

would become

... it would be wise to select the 0.15% max since this level MIGHT not require PWHT while the .2% CERTAINLY does.

... thus leaving the possibility of PWHT open rather than saying it positively isn't required.

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.