Dissimilar metal weld 1

[PMCap]

I have 2 pieces of 24" x 12" long pipe that are are each split longitudinally into to 2 halves.

One pipe is 304 stainless (P8) and the other is 1 1/4Cr1/2Mo (P11).

Each half pipe of each type material half pipes is welded to the other half pipe of the other material (P8 to P11) circumferential weld - P8 pipe is per ASME Section VIII, Div. 1 and P11 pipe is per B31.1 Code - wled is per B31.1 Code.

The he 2 sections are then welded together - 2 longitudinal joints.

How may I best transition from the longitudinal P8 to P8 weld into the longitudinal P11 to P11 weld. Question pertains to weld electrode used and weld procedure qualification.

Design pressure is 50 PSI and temperature is 300F? Material thicknesses are 1/2". Carbon content of (P11 to P11) material will be limited to avoid requirement for PWHT.

Do I need 2 or 3 weld procedure qualifications (P8 to P8), (P8 to P11) and (P11 to P11) or what? and how do I handle the transitionon between Codes and Metals regarding weld electrodes and weld procedure qualifications?

Thanks for any help in advance.

 

[davefitz]

I am a bit confused from your description.

As far as I know, B31.1 will not permit use of longitudinally welded P11 piping.

If this composite pipe will operate above 800F, then (a) you will need to consider use of a weld creep strength reduction factor of the longitudinal pipe and (b)you would need to use an incolnel weld electrode. The weld should be a very thick weld , and made with an automated welder, to ensure proper weld penetration ( a manual welder would turn down the amps to prevent weld spatter, but that would prevent adequate weld penetration).

 

[stanweld]

In order to make all the welds described; i.e., P8 to P8, P4 to P4 and P4 to P8, at least 3 procedures (procedure qualifications) are required per ASME IX. What engineering guru is responsible for this unique design?

 

[PMCap]

Thanks for the reply - Sorry, I misquoted the P-Nos. the P-Nos. are P8 and P4 (type P11 material). Would that change your answer.

 

[stanweld]

For the longitudinal welds between P4 and P8, one procedure is required. For any circumferential welds, assuming that you are welding the P8 sections (P8 to P8)together and the P4 sections (P4 to P4) together with the same filler metal used to make the P4 to P8 weld, two additional PQRs are required as stated previously.

 

[metengr]

Use 309 filler metal for the DMW's, 308 for the P8 joints and 8018 B2 for the P4 joints.

 

[davefitz]

Please note that mid wall cracking of DMW's that were welded using austenitic weld filler has been a major cause of boiler outages. The primary cause is alternating shear stress due to differential expansion between the P11/ P22 ferritic tube and 304 /316/347 SS tubes ( Shear stress is maximum at mid wall). In general, those failures were at tube butt welds in heated zones, where the range in temperatures at the weld interface may range from 60 F ( cold ambient) to 1125 F ( in service at full rating).

One might approximate the range in stress per startup-shutdown cycle as E(a1Tc-a2Th), E= youngs mod, a1=P11 thermal exp coef, Tc=60F, a2= SS thermal exp coef, Th= 1125F.

It is not pleasant to think of what such a cracking mechanism may mean to transfer pipes in the work space.

For tubine, good ( actually, excellent) availability was found by substituting stainless weld filler with incolnel weld, using the widest weld width feasible, welded with an automaic welder ( to ensure adequate penetration).

 

[metengr]

Design pressure is 50 PSI and temperature is 300F?

In the case above, Inconel filler metal is not necessary at 300 deg F.

 

[davefitz]

error- stress range would be estimated as E*Da*Dt, where Da= P11 therm exp coef -SS therm exp coef, DT= 1125F-60F.

 

[davefitz]

You are right again, Meteng.

 

[stanweld]

If the P4 to P4 weld section must be welded with ER80S-B2/E8018-B2, make sure that you complete that weld prior to the P8 to P8 section. Do not weld into the P8 material or A-8 deposited weld metal with the P-4 matching filler metal.