G40.21-38W Material

[yosamitysamm]

Hi All,

I have recently come across an issue with G40.21-38W material and I was wondering if anyone else has come across this problem and what steps they took.

On 2 seperate tanks I have recently worked on I have received material specified as 38W on the MTR. However on closer inspection it does not meet the additional chemistry requirements of API 650 Table 4.1. On the first tank I caught it before the material was used and we had it replaced, however, on the second tank I caught it during my final review. Now I have a tank where 70% of the shell material is not approved per API 650. My concern is I don't know if my tank now meets my MDMT of -40F. No impact testing of the plates has been done as it was impact test except to -40F. I also don't have any crops or cutouts that I can send for testing.
The specific item that the material fails is the Vanadium to Nitrogen ratio. API 650 specifies a minimum ratio of 4:1 but I have a ratio less than that. Any metalugists out there who know the significance of this ratio?

 

[yosamitysamm]

Has anyone ever recertified material to Grade 250? The way I read API 650, Grade 250 steel is a method of reclassifying steel from a foreign mill for use in API 650. My question is why is there so few restrictions on it? As per Table 4-2 the steel has to meet a few strength requirements and carbon content and then you could classify it as a Gr III material.

I don't understand how you can have so few requirements on a steel and then give it an impact test exemption to -40. I haven't found a reference to Gr250 elsewhere, is it defined in another spec?

 

[JStephen]

Do you have the manway and nozzle cut-outs from the tank? If so, that would let you test several pieces of the most critical plate.

 

[yosamitysamm]

Unfortunatly no. The material is not in the bottom course and no nozzles were installed in it.