Complete Annular Plate Replacement. Jacking?. Hydro Required?

[BlackOilsandBitumen]

Hi All,

I have a 24m diameter tank that requires replacement of all annular plates. First question do I jack the entire tank or replace the plates 1 by 1. I am thinking that jacking the tank will allow a better job of replacing the plates and that it will ultimatly be quicker as I can have multiple welders working at once.

Secondly. If I jack the entire tank does this force me to undergo hydrostatic testing? I believe that I would be able to exempt myself from hydro if I replace 1 by 1.

Obviously everything I do needs to comply with API 653. Ultimatly my goal is to get my tank back online as quickly as possible.

 

[IFRs]

Replacing the annular plates will trigger a hydro no mater how you do it. Jacking can be expensive and be time consuming. I'd suggest you slot the tank shell above the corner weld and slide annular plates in. You can have multiple crew working towards each other.

 

[BlackOilsandBitumen]

IFR's. Thankyou very much for you reply.

Are you able to slot and insert when only replacing the annular? I can just picture that the annular plates would need to angle down to meet the exiting floor plates and I would be nervous of overstressing at this critical area. I can see that if you installed a completely new floor above the old one this would be possible.

 

[BlackOilsandBitumen]

Sorry to gain a better idea of the suggestion. Is this what your talking about doing?

 

[IFRs]

Make your cut 1/2 inch above the toe of the existing corner weld. See section 9.10.2 and figure 10.1. Lap the new annular plate on top of the existing bottom plate using a fillet weld here. The new annular plates are butt welded to each other, with appropriate NDE per API 653.

 

[BlackOilsandBitumen]

Thank you again IFR's for you input. I appriciate all the help you have given me.

I have left my copy of the standards in the work place. If im not getting it I would really like a diagram of how to weld this !!. Or is it like this? pack up the difference with oil sand?

 

[IFRs]

The weld to the dead shell will not be possible given that the annular plate will project 2 inches past the shell. I would have thought that the old annular plate would be removed along with the old corner weld and portion of the shell and discarded. The tank will settle down onto the foundation and the slight angle of the annular plate as it slopes up to meet and lap over the bottom is of little or no consequence. The piping may need some support adjustment to compensate for the tank being lower by an inch or so. If you want to leave the existing annular plate and portion of the shell, see the sketch I have uploaded for one possibility.

 

[Duwe6]

BlackOilsandBitumen, you are overthinking your problem; just hire a reputable Tank contractor.
TANKO and Chicago Bridge & Iron are my favorite large firms. They ALL know what to do and how to replace an annular ring. They should ask you what NDT you want on the new ring section-to-section welds, and how far in you want to make the intersection of the new floor plate to existing floor plate joint.

When you try to specify construction details to professionals that have [several orders of magnitude] more knowledge and experience than you do, you are making a huge mistake. And yes, I've made that mistake.

 

[BlackOilsandBitumen]

Good Point Duwe6. I am down here in Australia and I have the main reputable tank company telling me to jack the tank. I then have local contractors that are very good welders and structual type people saying they could just insert plate (but they have little knowledge of API 653). So I really need to make a decision to fly in people and jack the tank or get the local people onto the job however I would more than likely need to specify to the local contractors how I want it done.

I need the tank back in service yesterday so time is more important than $ although that is a factor. Also I want the repair to be compliant and not give me problems down the track. If it makes any difference the tank is also an elevated temperature tank (200 deg C / 392 deg F)

 

[Duwe6]

Assuming that the reputable folks have seen your tank, either go with them or bring another experienced contractor for a second opinion -- just like we both would when looking for a surgeon.

Jacking is becoming more common in building new tanks - fab a ring, jack it up, fab another ring [under the first one], repeat. The fitters & welders can stay on the ground. If that is in the resume of the experienced folks, I'd sign a contract for them FAST. And unless you can hire an experienced tank erection/repair superintendent to run your job, don't hire the local folks. When you are out of time, you are out of room for repairs and mistakes.

I don't see that your hot liquid will cause any differences in the repair method. But I would require the floor-to-shell 'corner welds' be made using a low-hydrogen process, like FCAW. Preferably gas-shielded; FCAW-G [vs. FCAW-SS]. The gas-shielded wires tend to be more ductile, emit less smoke [makes for happier welders], and is easier to make good-looking big welds [happier inspectors].