API 650 SHELL PLATE MATERIAL

[stan000]

API 650 Tank shell plates 38 wt material
one piece is short can i used instead 50wt.
please advice.
Regards
stan

 

[JStephen]

Maybe. The permissible temperature ranges will be different for them, so the higher grade material needs to be adequate for the actual temperature. There are special requirements for welding, weld spacing, fabrication, stress relief, etc., with the Group IV materials that need to be addressed.

 

[stan000]

regular material 38 wt, cat 4 one piece is short it is difficult to get in time so I got 50 wt cat 4 material & chemical composition is in the range of 38 WT.
One course of shell needed 4 pieces of 96" x240" if one piece I use 50 wt will make any difference.
please advice.

Regards
stan

 

[JStephen]

Maybe I'm not understanding the question.
In Table 4.4b of API-650, I see material G40.21-38W listed under Groups II, III, and IIIA in various forms, material G40.21-50W listed under Groups IV, IVA, and V.
If that's the material you're talking about, then you're substituting a Group IV plate for a Group II/III plate.
And that means the exemption temperatures, welding requirements, weld spacing requirements, stress relief requirements, etc. are different for those two different plates.
So you can't just swap them out willy-nilly without looking into the details.
I don't know what "cat 4" is, and don't know what the "wt" means if it's not the "W" plates listed above.

 

[david339933]

It is the plates you listed...WT refers to impact tested material...the category is the test temp. Cat. 4 = -50F

 

[Geoff13]

With the Owner's approval it may be possible to recertify the 50WT as 38WT under clause 4.1.5. In that case the entire ring is now 38WT and no special requirements kick in. Just add your recertification letter and the customer's acceptance letter to the data book.

I know that there's enough overlap between 44W and 38W that this recertification is almost always possible. If fact sometimes the MTR will dual list both grades, which then eliminates recertifying. I don't recall trying to recertify a 50W as 38W so this may not be feasible.

 

[stan000]

thanks, friends
38wt cat 4 impact tested up to -50 same as 50 wt cat 4.
50 wt tensile stress is higher than 38 wt so we can use repads or any other attachments.
but if we do the butt joint with 38 wt technically no difference in notch toughness or tensile but as a formality approved by the customers needed.
regards
stan

 

[Geoff13]

Not sure I explained recertify carefully enough. The MTR needs to show that all values listed are within the 38WT permitted ranges.

For instance, 38WT has a permitted tensile range of 60-85 ksi, whereas the 50WT has a range of 65-95 ksi. There's a fair bit of ovelap, but only a review of your MTR will say if your plate has an actual tensile within the 38WT permitted range.

Similar types of differences exist for other properties and thus must be reviewed on the MTR for conformance with the 38WT limits. A partial list would include carbon, manganese and elongation.

If the values aren't all within the 38WT limits then you're back to all the problems listed by JStephen above.

 

[stan000]

yes absolutely
same I did to show the customer so it is easy to understand him.
thanks, regards.