Hardness Testing of Weld Cap in Field

[ukmet]

Dear and Respected,

We are performing hardness testing of field sour line piping joints. Is it possible to take hardness of weld cap? Our WPS got qualified with hardness of 225(Vicker). Our project requirement is 248max. Now the scenario is for weld joint hardness value come around 262 and in HAZ it comes around 195. I think this much difference is not possible. I read some where that in field weld cap hardness measurement is not possible due to irregular surface. Can you please guide? And what are the requirements in actual. To verify the PWHT and for other sour lines below 19mm do we need the hardness of HAZ and base metal or all three the weld metal , haz and base metal.

 

[metengr]

Yes, you can obtain reliable hardness readings of the weld cap with local surface preparation to provide a smooth surface with enough of a flat to allow a portable hardness tester probe. The HAZ will be more difficult because this is subjective as to location and method of testing. Base metal should be no problem. Why not measure the weld cap hardness and base metal hardness for comparison? If the WPS was qualified with hardness, accurate measurement of the weld cap hardness can be compared with the hardness of the weld coupon. Make it as simple as possible.

The hardness values you stated are rather large in comparison, 262 versus 195. What is the weld cap material you are testing and what type of portable hardness tester are you using for this work?

 

[ukmet]

We are using GE Technologies MIC 10. The material we are testing is A-333 Gr.6 and A 350 LF2. And some lines are of A-106 Gr.b and A-105. That is the reason we are not understanding the issue, the so much difference between two type of readings.

 

[metengr]

I am thinking your surface preparation could be the key because of the wide range in hardness values. Have you developed a procedure for surface prep and hardness testing to ensure testing personnel are following proper protocol in the field?

For your purposes, I would use the weld cap hardness and base material hardness only and forgo the HAZ hardness. My rationale is the weld cap hardness comes in under the max for PWHT, the surrounding region adjacent to the weld will be exposed to PWHT. Also, finding the exact location of the HAZ will be problematic in the field. Your objective is to confirm is PWHT was performed and hardness of the weld cap is what you need.

 

[weldstan]

As-welded hardness of deposited weld metal, especially the capping pass, is quite often much harder than the base metal HAZ and can easily approach 265 BHN depending on weld process, filler metal chemistry, base metal thickness, preheat and interpass temperature.