ASTM A335 Gr P11 allowable stress at temperature 3

[svi]

ASME B31.3 lists ASTM A335 Gr P11 material without any restriction on it's use at temperatures over a 1100 deg F. With the allowable stress of 20 Ksi at the min temperature to a low of 6.3 ksi at 1100 deg F. This is only 14% of the value at the min. temperature. Use of this material at these temperature ranges will result in a high wall thickness. Thickness over 13 mm will require heat treatment applied. It will be appropriate to use a matearial with higher allowable stress as other grades of Cr-Mo steels as P22 and higher. Is there any other code implied code restriction that may not allow the use of the P11 material at the temperature range of 1100 deg F. The allowable being so low at temperature, it becomes difficult to meet flexibilty, requiring larger loop lengths so as not to exceed the fractional allowble stress available.

 

[metengr]

The selection and use of material is up to the designer or Engineer. The Code does provide cautionary statements regarding use of certain materials. In this case, if allowable stresses go up to the maximum temperature one can use this material up to this limit. Yes, it would be more appropiate to select an upgraded material.

 

[davefitz]

svi,

Over 1000F one should be considering T22, T23, t24, T91, T92, austenitics. In addition to issues of weight and flexibility there are also issues of corrosion and ease of fabrication.

"Nobody expects the Spanish Inquisition! "

 

[stanweld]

While B31.3 permits grade P11 to be used up to 1200F, it doesn't imply that is should be.

 

[svi]

davefitz,
What is the T22 designation? Is it the same as the P22.

http://www.s-k-h.com/media/de/Servi...sch/Kesselrohre_EN/10CrMo910_P22_T22_engl.pdf

The alternate designation depicting the composition is misleading, '10CrMo9-10'

stanweld,
I am trying to counter a contractor who insists that he is code compliant and therefore correct about his material selection of the P11 for the 1100 deg F service temperature. I can see his position, having made the piping system. It is costly to undo it.

 

[metengr]

svi;
This is a contractual problem, and not a technical problem. Good luck with trying to undo this mess. There is nothing in the Code to prohibit this material for use at 1100 deg F. I absolutely agree it is not the material choice but this is where experience comes into play.

 

[stanweld]

If you have given the Contractor carte blanche with regard to material selection, you now see your company's error. If the pressure is very low and the wall thickness is kept reasonably thin, it may have been the most economic choice, but from what you are telling us, it appears not so. Most Owner/Engineers are specifying a maximum temp for P11 at 1000F based on literally hundreds of specification that I have reviewed over my career.

By the way, per B31.3, Table A-1, the design allowable at 1100 F is 2,800 psi.

 

[svi]

A material wise temperature limitation. That must be included into the piping class definition?

The regeneration case of the reactor is what has this high temperature, but at a lower pressure of about 10 bar g.

Will it be appropriate to have a Company specification that will limit the induced operating stress to say 80% of the code allowable expansion stress range? The intent of this being that there will be an additional margin for uncertainities as route changes, fabrication errors and other.
I happened to read a post in eng-tips that ASME B31 may be including an allowable for the operating condition.

 

[stanweld]

Depending on the normal operating temperature of the pipe, I would be highly concerned with thermal fatigue during the regeneation process depending on the number of annual regeneration cycles.

 

[davefitz]

SVI,

I do not know the specifics of your reactor, but some reactors have issues related to hydrogen damage during the regeneration cycle- if this is applicable, there may be other metallurgical concepts to be reviewed when selecting a material for a reactor.

"Nobody expects the Spanish Inquisition! "

 

[jtseng123]

We use 1 1/4Cr as high as 1050F on FCC reactors and piping. For piping, a lot of loops or large bend has to be made without question for thermal expansion and no way to avoid unless expansion joint is used.
You can not counter with your vendor if you do not specify higher grade material in the begining. You are going to loose the fight.
How much % below the code allowable, it is personal preference. 90-95% of the code allowable is good to me in your case since regeneration is a short term operation, pushing to the limit shall not be a problem. No one is going to challenge you as long as you meet the code allowable. Be sure you have all weights counted including insulation. Many times, weights are underestimated that will cause problem because it is very sensitive for low allowable stress at high temp.

 

[davefitz]

The number and size of expansion loops can be greatly reduced if one used a stronger material. The thinner wall leads to a much lower section modulus, which in turn lowers the reactions at the presszure vessel nozzles.

10 yrs ago, in London, there was a paper delivered by Alstom/CE on the economic advantages of using p91 in lieu of P22 piping, and the 2 primary savings were related to (a) lower metal mass results in savings in supports and(b) lower section modulus rsults in much fewer expansion loops, both are due to the much thinner wall thickness.

"Nobody expects the Spanish Inquisition! "