Decarburized surface of SA335-P91 pipe

[Pipoy04]

Dear All,

When conducting hardness test on P91 pipe, the hardness value is less than the requirements of our project. Our company sets a range of 190-265 Hv hardness of the base metal, but some of our reading is less than 190 Hv.

I would like to know the correct surface preparation in order to achieve the decarburized surface of the tested material?
How deep we will grind the surface of the material tested?

We are using portable device with a "D" probe, which measures the impact and rebound velocities of the test tip that is projected at the surface under consideration. The device converts the measurements into a hardness value, the so-called Leeb Hardness (LH).

 

[metengr]

The decarburized layer varies, I have seen where grinding is done in increments and portable hardness testing is performed to trend the hardness. Other times I have seen where grinding is performed to a depth of 0.030" with hardness testing. If the hardness exceeds the minimum, no further grinding/testing is performed.

See the free reference document below, it is a must for handling Grade 91 steel and has a section on hardness testing D-1;

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000003002006390