Roof Plate Welding

[Forging09]

Hi All,

I would like to ask a question regarding roof plate welding.

Currently we can not convince our consulting company. we designed roof plate overlapped each other in 50mm gaps and its welding is single side at the upside only. According to API650 ,single weld is applied and it is adequate. But Consulting forces us to apply double side welding both upside and downside welding. They claim that due to corrosion effect ,double side is wanted also at downside.

How can i convince them?

Your comment is appreciated...

(Note: Tank is water tank,roof plate thk=6mm(including 1mm corrosion allowance) ,Roof will be coated by 300 microns paint)

 

[IFRs]

If they will not use the code, what use is the code? AWWA (American Water Works Association) also has single sided welds.

 

[FTank]

If roof is interior coated, all seams should be welded on the inside or else surface prep and coating will not be effective. (fer to NACE RP-0178.

 

[JStephen]

This is not a technical issue, but a contractual issue. Both AWWA D100 and API-650 allow lap-welding of roof seams from the top side only. Both also permit seal-welding of the underside, as well as seal-welding of structural members to the roof plate. However, the seal welding is not required by the standard, and must be specified by the customer if it is required. Read your contract, see if it's required; if not, request a change order to do it.

 

[Forging09]

Thanks you all for replies...

 

[vesselguy]

Forging09,
I have the same comment as FTank. Your Client is right. It is not a strength issue. If the tank roof is internally coated, all joints must be seal welded. Otherwise, the unsealed area will be the source for future corrosion and will waste the effort and cost for internal coating. This is pretty much covered by many tank coating specifications. Note that you also have to seal the roof to shell compression ring joint with a caulking after coating.

 

[AK8824]

I have a 46 m dia water tank. I have a feeling that lap-welding should not be used. The tank needs to be internally lined as well. How do I line the trusses inside the tank? It would be extremely difficult to get holiday-free coating.

Any information on internal lining will be appreciated.

Geodesic dome roof tanks: are they widely used in water service?

Cheers!