WP11 hardness

[MFQC]

Hi
In portable hardness test of a 28 inch WP11 tee we had some problem. As standards mentioned, before testing we should remove all oxides ,paint,.....
We prepare surface with a grinder till we visually see bright mirror like surface. The result of hardness test was 215 brinnel. We checked the thickness. By our first preparation ,the thickness decreased 0.1mm. I suggested to grind 0.1mm more and the results became within the range of standard ,about 170 brinnel.
Are we allowed to do the above mentioned process according to astm standards.
Thanks

 

[weldstan]

Are you the manufacturer or the Buyer? If you are the Buyer, the hardness testing is up to you.
As I remember, there was no hardness test requirement for WP11 but I may well be wrong. Do read the ASTM specification for the grade.

 

[MFQC]

Dear weldstan
We are the buyer. But some of my friends believe that by grinding 0.1mm more from the surface would alter the real surface hardness and that may cause failure from the surface(which have the higher hardness) in the future. You were right about the hardness requirements for wp11 .But as I said ,the tee was 28 inch and we couldn't do destructive tests. So we just performed PIM and surface hardness measurement.
Thanks

 

[weldstan]

A small spot ground and polished will not affect the overall strength of your Tee. Your hardness test should only be done to validate the manufacturer's MTR for the part. Because the minimum tensile strength of WP11 is so low and most WP11 will be much stronger than the minimum tensile properties mandated (essentially for fully annealed heat treatment), I would not require hardness testing of the material, only PMI to confirm chemistry.

 

[MFQC]

Dear weldstan
But as you know according to SA234-wp11 there's limitation on maximum hardness. Maximum hardness is 201 HB.
Thnks

 

[weldstan]

With a max hardness requirement, the hardness should be stated on the MTR. As a receiving inspection by the Buyer, I would still only recommend a PMI. A tellebrinneler test on a filed surface would negate some of the surface effects that influence your test equipment (assumed sonodur type - MIC 10 or equivalent).

 

[MFQC]

Dear weldstan
I agree with you about the problems of portable hardness testers. But when you don't have MTR or when you don't receive MTR ontime, what do you recommend? In this case we couldn't do destructive tests. So if you just do PMI,how would you assure about the mechanical properties?
Thanks

 

[weldstan]

If you don't have the MTR, then I would advise both PMI and hardness testing as a receiving inspection prior to installing.

One must ask, why was the Tee purchased without an MTR supplied at receipt?