hardness problem

[sadra]

hi
we qualified pqr for inconel 625 clad material(API 5L X65+
3mm inconel 625).the maximum hardness in HAZ on base metal is 252 HV10. our service is soure according to NACE MR 0175.hardness is acceptable or not?
thanks and regards.
R.Salimi

 

[Carburize]

I would say yes. NACE MR 01 75 defines hardness limits using Rockwell C scale - 248HV according to ASTM E 140 reference tables equates to 22Rc.

 

[TomEun]

Sadra,

I think you have to consider the hardness requirements for overlay/clad surface (Inconel 625) and base metal (carbon steel) together.

MR0175 requires the hardness limitation, maximum 35 HRC for Inconel 625 and maximum 22 HRC for carbon steel. For the base metal of your concern, the actual hardness, 252 HV is over than 248HV (max. value). Therefore the stress relieving is required.

Hardness Test and Conversion Table;

http://www.gordonengland.co.uk/hardness/index.htm

Thomas

 

[Carburize]

In NACE MR 01 75, Rockwell C is the definitive hardness measurement so in case of any dispute this is the test which should be performed to confirm acceptance - I would be very surprised if an HAZ which gave a value of 252 HV10 did not show less than 22Rc

 

[sadra]

hi
I agree with all of you.hardness is more than 22HRC but
where inconel 625 clad carbon steel is used in NACE service
the hardness requirements of the nace document are not
applicable as the inconel 625 cladding dose not corrode and
hence there is no evolution of atomoic hydrogen.therefore the risk of sour service SCC is elimineted.am I right or not?

 

[Carburize]

Not according to the NACE MR 01 75 document - to be acceptable for sour service the base material and HAZ must meet the hardness requirements even if the part is fully clad with corrosion resistant alloy.

 

[sayee1]

Strictly speaking, the weld is not acceptable as is. But there are ways to gt the weld acceptable. One for e.g. would be to carry out hardness as per Rockwell C. The indent/indentor size being bigger in that case as compared to HV10 scale, it is sure to be within the maximum limit of NACE i.e. 248HV10. Used this approach especially for sour service gas pipelines. One word of caution though, you might have to deviate slightly from the indent locations if specified in the client specifications for the PQR using HV10, because of the difference in the indent sizes.
The second approach would be to justify the readings you have already obtained. How many readings are above 248 and what is the location of these higher hardness readings? Are they closer to the root or closer to the cap? Some codes and specs give different limits for different locations? Is that true in your case ? If not I'd use an approach to justify the higher hardness if it is closer to the cap using this approach and based on EFC 16 where the root hardness permitted is 248 HV10 maximum but cap hardness permitted is upto 275 HV10. This approach woulde need a careful evaluation and a proper justification.....


Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
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