Adjacent Shell plates of different thicknesses in the same course

[EfficientPuppy]

Is there somewhere in any of the code books (API 650/620 AWWA D100) that addresses using a different shell plate for adjacent plates in the same course? I seems to remember reading about it, but I can't remember if its addressed in a code book and I cannot seem to find it.

 

[IFRs]

For a new tank or a tank being repaired or having been repaired?

 

[JStephen]

I'm not aware of any requirement relating to that, which should mean that it's allowed.
Under older versions of API-650, flush manway insert plates were specifically required to be 1/16" to 1/8" thicker than adjacent plate, so certainly it can be done.
It's somewhat undesirable, as having a thicker plate makes that portion of the shell stiffer, so stresses adjacent to the thick plate are likely higher than they would be with uniform thickness.

 

[IFRs]

API 650 includes thickened shell plate for penetrations but does not forsee a company wanting to used uneconomical plate in a new tank. If it is more than 1/8" thicker than adjacent plate at horizontal or vertical joints you'd want to see a 4:1 bevel. Is it thicker because it is a different material grade or strencth?

 

[EfficientPuppy]

Is it thicker because it is a different material grade or strencth?

We have a cone bottom elevated tank with a nozzle placed super close to the column extensions up the tank walls. API 620 5.14.5 requires the nozzle reinforcement to be 6 in from the nozzle reinforcement, which in this case is just simply not possible. However the note to that section says that if there isn't any need for reinforcement than the the dimension is measured from the neck of the nozzle, which is manageable. So the suggestion was thrown out that we just thicken the 20' section of plate that the nozzle and bevel its edges to eliminate the need for a reinforcement. I'm not sure we are tripping over dollars to save dimes here, however, this a fairly large tank and this plate is thick, so we are trying to see what options we have to prevent thickening the entire course. So if someone else as encountered a similar issue that has a better suggestion that Id appreciate that. I suggested a thickened insert plate also, but I'm not sure if that qualifies as reinforcement, or as a patch of thick shell. Truthfully, I don't totally see how a thickened tank section is really any different than thickened insert. I guess if that is the suggestion than that's a battle I'm willing to fight.

 

[IFRs]

Why can't you move the nozzle?

How large is this nozzle, how thick is the tank shell, what is the diameter of the tank?
How much thicker are you looking at?

For reinforcement:
Could you thicken a smaller section of shell plate just in the area around the nozzle?
Does using a thicker nozzle neck get you the reinforing you need?

 

[r6155]

What exactly is the code, API 650 or API 620?

Regards

 

[EfficientPuppy]

We are using API 620. I was looking for anything in any code so I could reference it for my best judgement.

We can't move the nozzle. The columns can be moved to some extent, but not enough to solve the issue.

I haven't looked into different reinforcement configurations, admittedly I've just been doing the typical double the shell playe approach. But I'm doubtful accounting for the nozzle and excess shell will account for much here.

 

[JStephen]

If the nozzle is not too large, look into using heavier-wall pipe, or a long-weld-neck flange, or heavy-barrel flange to get the desired reinforcing.

If the tank is not actually an API-620 tank (ie, some sort of non-code hopper that doesn't fit into any other standard either), then consider just taking exception to the standard.

 

[r6155]

Does this tank have thermal insulation?.

Regards