Using thickened sheet plates to patches shell plates courses. 2

[Youcef40]

Dear Experts,

we have an issue with the disponible of original sheet plates of 5mm thickness, in order to repair one of our storage tank shell plates. the only thickness disponible at our level is 6 mm and 8 mm.

please could you advise if we can use ticked plate to patches or full replacement the original shell plates 5mm.

Regards.

 

[HTURKAK]

Copy and paste of relevant clauses from API 653,

9.3.1.3 Except as permitted in 9.3.3.2 and 9.3.4.3, the repair plate material shall be the smaller of 1/2 in. or the
thickness of the shell plate adjacent to the repairs, but not less than 3/16 in.

9.3.3.2 The repair plate thickness shall not exceed the shell plate thickness at the perimeter of the repair plate by
more than one-third, but no more than 1/8 in. The repair plate thickness shall not exceed 1/2 in.

In this case, if shell thk. 5 mm, you may use 6 mm patch plate thickness.




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[IFRs]

I think the above response is for lap patches, which you also have to be aware has a much lower joint efficience than butt patches. If you are using butt patches you can use thicker material almost wihtout limit as long as you use a 4:1 bevel when the thickness difference is over 1/8".

 

[Youcef40]

Dear Sir IFRs

but I in API 653 not mentioned butt patches only lap patches, we can use butt patches on the shell course?

 

[IFRs]

Butt patches are almost always better. They are in API 653.

 

[HTURKAK]

I know shell plate repairs with ( by Weld Metal Deposit, by Lap-welded patches and replacement of shell plate material)
As far as i understand , you call '' butt patches'' the replacement of shell plate. I am not sure if this is correct wording .







Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[IFRs]

I was using the wording "butt patches" to distinguish between lap-welded and butt-welded repairs. Butt-welded would be the same as "replacement shell plate" unless the shell was originally lap welded or riveted, in which case it might help to specify "butt-welded" in the repair scope. I apologize for confusing posts.

 

[Dhurjati Sen]

HTURKAK Sir, I salute you.

DHURJATI SEN
Kolkata, India