replacement of annular ring

[APItips]

Hi guys
a catacarb storage tank was out of service for internal inspection, severe underside corrosion was noted all around the annular ring detected using UT. Full replacement of all annular ring plates is going on at the moment by cutting through the shell and bottom weld and slotting the new plate section by section and sequence method.

My question:
Should the butt welds of the annular ring be radiographed? API 653 says so for a reconstructed tank but my case is only replacement of annular ring plates. if yes I think there will be no access for the other side.
A vacuum box test will be conducted On completion of all welds and 24 hours hydrotest.

your replies are highly appreciated.

Thanks

 

[fegenbush]

Per API 650 8.1.2.9, either 10% or 50% of the radial joints shall be radiographed based on whether double butt welding or single butt welding with permanent or removable backing is used.

Since you are saying that you have no access to the back side of the material, it is assumed that you will be single butt welding. In that case, assemble two annular ring segments out of place and radiograph as required. Then place the subassembly. If you do this, 50% of the joints will be radiographed in accordance with the standard.

 

[APItips]

Hi fegenbush
Thanks for your reply
This is a great answer. but what about the weld between the annular ring and the bottom plates. Basically, in my case it is a butt weld.

Regrads

 

[fegenbush]

Radiography for the joint between the bottom plates and annular ring is not required by API 650 8.1.2.9 and API 653 12.2.1.4. In most cases this is a lap weld, thus no radiography is performed. Even though yours are butt welded joints, radiography is not required. Your vacuum box test and hydrostatic test are sufficient for this joint.

 

[Samm17]

Note that in Sect 8.1.2.9 that it states that the RT is only required if the annular is required per 5.5.1 or M.4.1. Often an annular ring is installed on a tank even though it is not required per the 2 sections mentioned above. In this instance I would argue that API 650 does not require you to do any RT on the annular ring.

 

[Duwe6]

". . what about the weld between the annular ring and the bottom plates?"

IMHO, the best test is to complete the inner weld first, and apply diesel/kerosene on the outer area. This is a standard API test, and if it is allowed to 'penetrate' for 8 hours or more, is VERY sensitive to thru-and-thru porosity [much more than vacuum-box testing]. After any repairs are made inside, take a torch [preferably propane, with a fat, 'soft' flame - no overheating of the steel] and burn off the diesel prior to making the outside 'corner weld' [shell-to-ring]

 

[fegenbush]

Duwe6,

I think you are talking about the corner joint between the annular plates and the first shell course. I was under the impression that the question was referring to the annular plate to interior plate welds, both being on the floor.

 

[LurmClaxton]

Does anyone use shearwave in lieu of radiography on radial annular butts?

 

[Duwe6]

I do. However, the current 'state' of API-650 & 653 require phased-array with data aquisition for 'proper' UT in lieu of RT. Thus manual UT* fails to meet the letter of API, at the moment. Maybe somebody will come to their senses in Houston. Or not.

*manual UT shearwave obtains the same data as phased array w/data aquisition. Except that the aquisition and processing takes place between the ears of the UT tech, and not inside the PA unit. And the 'between the ears' memory is very volatile. I'm guessing that due to a number of poor-quality UT techs, API has chosen to disallow that method.
FWIW - I do both manual and PAUT. Lack-of-fusion is still 'LF' and still rejectable. The problem seems to be "How much porosity is too much?", but I haven't heard the API Committee's reasoning.