Hardness difference

[pdp123]

Hi to All respected and Experienced members...

-There is a Hardness difference in Seat and Disc of valves and the value is restricted to 150BHN.
Please explain the purpose of Hardness difference.
Per my understanding there is an impact on Trim material selection and the more the Hardness difference the valve can be easily use for Harsh and corrosive conditions.

Thanks


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[gerhardl]

Not exactly. There are a lot of mechanical and chemical factors and properties both for sealings and seats that will have an influence of sealing properties over time, along with purity and property of the fluid.

But yes, for some constructions, for instance for ball valves, a harder material is welded on a (steel) seat to give better (corrosive also) resistance over time.

 

[SJmetallurgist]

I understand that this differential hardness limit is specified by the user.
This limit is given simply to avoid damage done from one part to another. By regular closing and opening action, there could be damage done form the harder part to the other. Normally this differential is restricted to 50BHN. A value of 150 BHN looks a tad higher to me. Trust I could bring some clarity to you.