Chrome Molly to Carbon Steel Welding 1

[EJWhite]

Welding a P-11 pipe to a P-1 tank do I need to Post Weld Heat Treat the weld or is there a thickness or preheat loop hole in ASME Section IX? Tank is 3/8" nominal SA-516-70 material. Pipe is SA-335-P11. I can also change from P-11 to P-22 or P-5.

 

[PAN]

Please be informed that ASTM A335-P11 is not P-Number 11 in ASME Section IX. This is 1.25%Cr - 0.5%Mo Steel, which is P-Number 3. If you really would like to weld plain carbon steel to low alloy steel, the PWHT should be carried out. I recommended 710-740 Degree C (1 hr.) for holding temperature.

However, I still would like to ask you to re-consider again. What's the reason to use A335-P11 as nozzle for A516-70 Tank?

 

[johnc01]

Would you not be better to confirm that heat treatment is mandatory before looking for loophole in asme ix,has the code you are working to determined that pwht is required,or where is there a spec break between piping and tank? what is wall thickness of pipe,does owner requirements call for pwht regardless of thickness or does it give exceptions,if PWHT is not required then, i think i am correct in saying that there is no need to qualify a procedure

If it was for process piping alone, for example,ASME B31.3 table 331.1.1 for P3 alloy steels,equal to or less than 1/2% cr, equal to or less than 19mm, equal to or less than 490KPa/71ksi, no heat treatment,for P4 alloy steel material, equal to or less than 13mm, equal to or less than 490KPa/71ksi, no heat treatment is required, same table for P5A,5B, 5C equal to or less than 3%Cr/0.15%C, equal to or less than 13mm, all MPa/ksi. no heat treatment is required.

Also Para 331.1.3 gives governing thickness criteria for pwht on branch connections, fillet welds, external non pressure parts etc.

Maybe someone else can give you their opinion as well as this is only my interpretation, but i tend to agree with Pan and look at reason for using this class of pipe,hope this helps

 

[EJWhite]

The tank is an HRSG Blowdown and is in line downstream from a boiler. These tanks are used to expend an overflow of steam. The piping from the boiler is Chrome Molly and the engineering house wants to use chrome nozzles in the vessels. Design Temperature is 710° F @ 150 PSIG.

The ASME Code is clear that we are required to PWHT however I'm not comfortable with the disimilar metals during the process. These nozzles are tangental and the tank is as I said before carbon steel and then there is a stainless steel wear plate on the inside. All three metals will be welded together at the nozzle junction and then heat treated at 1,150°. You can see why I have concerns and why I am looking for a loop hole.

Thanks...

 

[rustbuster1]

Boy-o-boy, that engineering house needs more "engineering" skill.
Why is Cr-Mo steel necessary at 710F?
If the impinged surface in the tank needs a SS surface, why not make the inlet nozzle SS too and bolt/weld the steam pipe to it?
Why are they not interested in constructibility issues? What about using preheat inlieu of PWHT - a common practice where such complexity arises?

This sounds like 150 psi steam going into an accumulator - all the fancy materials seem unwarranted to me.

 

[lalaith]

First of all SA335-P11 is P No. 4 material not P3, the P11 is a group number not a P number. To determine the need for PWHT you would have to tell us the Schedule/wall thickness of the material. You do not have to PWHT P4 material provided; it is 1/2 thick or less, has a carbon content of .015 or less and you maintain a weld preheat temperature of 300 degrees.

Sorry I am so late on this response....perhaps you can use it for further instances of this situation.

 

[PAN]

My first reply about P-No. is incorrect as lalaith's comment.

 

The alloy steel nozzle appears to be a good choice, to prevent erosion, especially for wet steam service. My experience is that following sound engineering principles, which includes complying with ASME Code requirements, will ensure safe operation. The application of preheat or PWHT is intended to minimize hardened heat affected zones which are susceptible to cracking. Loopholes can lead to unsafe equipment and major liability. Bob

 

[pipewelder1999]

The national board inspection code used to have alternative methods for PWHT.

If this is a repair or alteration then that along with governing state codes may be used.

 

Please tell me what is the exact meaning of nominal material thickness in asme IX ,for example if I am doing a socket weld to joint a 2"pipe p1 to a 2"valve P5a and if the thickness of valve socket is 3/4" do i need to do pwht? WHY?

 

Please tell me what is the exact meaning of nominal material thickness in asme IX ,for example if I am doing a socket weld to joint a 2"pipe p1 to a 2"valve P5a and if the thickness of valve socket is 3/4" do i need to do pwht? WHY?

 

[pandithan]

first ASME SEC 1X does not indicate the requirement of PWHT for P4 materials and you have to refer ASME SEC V111 div 1 only. pwht is required for p4 matl is to improve the ductility which will become hardened while welding. refer the section v111 div 1 for the excemption