Why NICKLE is not taken into consideration in PREN(Pitting resistance equivalent number) 10

[Jason8zhu]

Dear All,

PREN is a vital number to roughly evaluate the
corrosion resistance of CRA(Corrosion Resistance Alloy),
in which Chrome(Cr) and Nickle(Ni) are importance element.

In calculating PREN,percentages of Cr/Mo/Nitrogen and even tungsten(W) are included.
Would anybody share with me, why Nickle(Ni) is excluded ? Thanks.

 

[EdStainless]

Nicky, CSCC has noting to do with pitting and crevice corrosion except that both start with a breakdown of the passive film. PREN is related to pitting only. It is an empirical correlation between results of G48 testing and composition.
SCC resistance is a very complicated issue. You will recall that alloys with little to no Ni (ferritic, which is interesting since these alloys are very susceptible to hydrogen cracking) and alloys with a lot of Ni (generally over 40%) are virtually immune to CSCC.

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P.E. Metallurgy, Plymouth Tube

 

[nickypaliwal]

Thanks to all your expert comments here.. good discussion for young engineers like me..

 

[nickypaliwal]

Although old post, still would like your comments on below query:


Do we need to consider same chloride content in water, gas and Oil outlet line from test separator for Material Selection ?

Though simulation shows gas phase in gas outlet but there can be water carryover in the phase.

Also about water outlet ?