Hardness value on Weld metal after PWHT for A106 Gr. B 2

[Elyaas1987]

Good day to all...
we had used the consumables (ER70S-2)/OK TIG ROD 12.62, size: 2.4mm dia for our production weld joints (pipe materials: carbon steel ASTM A106 Gr.B; size: 3 inch; Sch 40). Further to inform you that we had checked the hardness of base material, HAZ and on weld metal before & after PWHT, below hardness readings were observed

HARDNESS VALUES BEFORE PWHT
1. Base material: 130-150 HB
2. HAZ : 140-160 HB
3. Weld metal : 170-190 HB

HARDNESS VALUES AFTER PWHT
1. Base material: 120-140 HB
2. HAZ : 130-150 HB
3. Weld metal : 210-250 HB

After performing PWHT the hardness value of base material and HAZ has reduced whereas hardness value of weld deposition has been increased (which is beyond the acceptable limit)

I would like to know from you that what might be the technical reason/root cause for increase in hardness only on the weld metal after PWHT.

Note:
We have used all kinds of filler wire brands and attained the same hardness value.
we have even utilized 3rd party PWHT company to perform on mock up coupon and again the same issue.
The service of the piping is AMINE and client says it is mandatory to do PWHT and values shall be within 200 HB

Please share your experience on the above issue.

 

When it comes to hardness of carbon steel weld metal increasing after PWHT, I have no experience to share.
Your data indicate testing with HB, an abbreviation for Brinell. Brinell method is utterly inappropriate for testing of weld cross sections. I suspect that is the real problem.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

Assuming that they filed the weld deposit after PWHT, the only reason to get higher hardness is secondary precipitation during PWHT. Check the chemistry of the deposited weld metal. I have seen hardness testing done improperly over the oxide layer and record higher hardness.