Shop/ Pre-Fabricated Tanks

[anba1696]

Dear All,

We have designed a brown field storage tank terminal (Mainly Chemicals, Partially hydrocarbons) for one of our clients located in the UAE. The tank diameters are 9M and 11M. One of the EPC Contractor came out with a suggestion of prefabricating these tanks and erect/install at the location. As per API-650 Appendix - J, the same is however permitted only for the tanks having diameter 6M and below.

With the recent fire in the Jabel Ali Free Zone, Dubai, client has asked us to review the EPC Contractors request, as prefabricated tank will reduce lot of site welding and in effect will increase safety. We are in a situation where the Contractor is confident of doing the work in shop and erecting at site, shop fabricated tanks will have better quality and adds to safety at site but API 650 does not allow the same.

Can the forum give the direction to this subject?

Thanks in advance,

Best Regards,
A.Raghuraman
araghuraman123@yahoo.co.in

 

[IFRs]

API 650 Annex J limits the design of shop-built tanks to those 6 meters in diameter or less. Note that the language does not restrict the shop fabrication of tanks over 6 meters, just their design. The main standard does not specifically say it is only to be used for field erected tanks. Section 1.1.5 is the only place I found where shop fabricated tanks are mentioned at all in the main body of the code. While you can not say that your tanks will be Annex J tanks, I would use the more restrictive of Annex J and the main standard to design, fabricate and test. This is a fairly literal interpretation of the language in API 650 and may not represent the intent of the code. These are my thoughts only and should in no way be taken to be representative of API, the committee, the code or good engineering judgment.

 

[LittleInch]

How much of the tank is he intending to pre fabricate? A 9m tank is not practical to transport, so to me the issue is not so much the design, but the different installation techniques compared to site built tanks.

650 is clearly intended to relate to site built tanks above 6m, bigger than that being transported and erected as a single thing needs more support and rigidity to withstand transport and lifting into place than a site built tank and hence the design would be different. Building on site from larger sections than normal however is a different thing. If you can provide a bit more info that would be useful.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[JohnGP]

On my previous project, we had tanks mainly up 12m diameter (plus one about 13.5m) shop fabricated and shipped to site, mainly due to the extremely high cost of site fabrication. They weren't classed as Annex J tanks, but as IFRs highlights, elements of Annex J were included in the design. Butt welding the floor plates was considered necessary, and we came up with a simple cable support system for the floor. Additional lugs were provided externally following consultation with transport and shipping companies so that sufficient tie down points were available for the sea journey, and during movement to and from the ports.

As I recall there were no problems experienced with such construction, transport, and installation, but does require careful planning. Having the shop and site close to nearby ports makes the job a bit easier.