max hardness after PWHT of P4 & P15E matl? 3

[qcrobert]

Could you help me on where to find the max hardness value after post weld heat treatment of P4 & P15E materials.

the construction codes are either B31.1 or ASME sec 8, we have done a welding procedure qualification test and we got some hardness values, but do not know whether the hardness readings taken are acceptable.

there is a brinell hardness max in table 331.1.1 of B31.3 but could not find it in either B31.1 or ASME sec 8

Thank you in advance for any assistance or guidance

 

[stanweld]

As you have discovered there are no hardness requirements in B31.1, Section I or Section VIII for the welds in question. What was the filler metal chosen?

EPRI, in its 2011 publication, recommends a maximum hardness of 280 BHN for P91 to P91 welds using "B9" filler - the same can be applied to P4-P15E using "B9" filler. Additional PWHT should be performed if hardness excceds 280 BHN. The desired range is 190 BHN to 250 BHN after all welding & PWHT has been performed. When welding with a "B3" filler metal the 250 BHN max should be considered.

 

[metengr]

The main reason hardness testing is not and will probably not be used for B31.1, Section I or Section VIII applications is because of interpretation of results. A procedure should be qualified for hardness testing, even for information purposes, because lack of surface preparation is what results in highly variable hardness test results.

The EPRI document which is a guideline for fabrication of CSEF steels and mentioned by stanweld should be used as a guide only. It was developed based on a tailored colaberation project and it was decided to make it public to promote safety with use of CSEF steels.

 

[stanweld]

Early work, indicated a lowering of Creep properties when P91 hardness exceeded 300 BHN. Agree with metengr, the EPRI publication is a guide - not a mandate; however, a number of Owner/Operators are promoting strict adherence thereto.

Based on extensive microscopy and mechanical testing, low hardness in P91 base materials and weld is believed more likely to lead to premature failure in service. We have seen P91 materials improperly heat treated with very high hardness (> 380 BHN) fail hydrotest due to stress corrosion cracking.

 

[qcrobert]

P4 - E8018-B2
P15E - E9018-B3

It is a pipe attached to pressure vessel and the connecting pipe is under B31.1

The thk of 6" pipe we used during procedure qualification test was 11mm.
Heat was brought up to 730deg C with soaking period of 1hr as per B31.1 / sec VIII.

If you refer to B31.3, the soaking period for this material is 2hr min.

The max BHN obtained is 290 at HAZ. Do you think the 1hr soaking period as applied is not enough?

Thank you,
Robert

 

[metengr]

I presume the above information is from a WPS qualification. The hardness for the weld metal/HAZ side of Grade 91 is higher than I would like. Typically, this value should be 270 for PWHT performed within the desired band of 750-780 deg C. Your hold time is not the issue, it is the PWHT temperature being at 730 deg C, the very low end of the range.

 

[stanweld]

I require a 2 hr min hold time for welds similar to that described and have done so for the past 17 years with no welds exhibiting such high hardness (assuming that your hardness test measurement is correct). For the past 7 1/2 years, all welds in P91 and dissimilar metals welds have been subject to hardness testing.

 

[davefitz]

The tempering correlation for PWHT of P91 that has been bandied about lately ( source NEM) is as follows:
objective: weld zone hadrness < 270 Hv

LMP=21= T*(20+log(t)) /1000
T= holding temperature, K
t= holdng time, hrs
LMP= larson miller parameter for PWHT tempering
some rough values for a LMP=21 are:
1400 F for 2 hrs 10 min
1375 F for 4 hrs
1350 F for 7hrs 40 min

some other minor points voiced lately are:
-must add thermocouples directly under heating coil to avoid overheat of metal directly under coil. The amount of overheat that occurs directly under the center of coil mass is roughly proportional to the temperature ramp rate times the square of distance from the center of the coil to the weld zone monitoring thermocouples. Some data shows this can be more than 100F over the weld zone , if the istance is alrge or the ramp rate is excessive. Exceeding 1470 F can occur if your not careful

- Siemens claims that repair welds must be PWHT'd about 25F below the original weld's PWHT holding tep, but others claim this is hogwash and not relevant to P91

 

[Guest102023]

How much validity does LMP maintain when a 'stress relief' includes 'tempering' with significant metallurgical changes? It seems more difficult to make hard and fast rules for the CSEFs.

I agree the problems really begin when the rubber hits the road - the capability of the constructor and the difficulties of field hardness testing.

stanweld,
What is the number of that 2011 EPRI document?

 

[stanweld]

1023199 dated November 2011