Storage Tank spec.

[yanuarsaja]

Hi all,
i am new in Storage Tank area, i have question:
- is continously filled weld mandatory for roof plate lap joint if a tank roof is internally lined or coated (both inside and outside)?
or seal weld is enough?

- Emergency Vent requirement, is there any mandatory requirement to use it? let say for water storage tank, is not mandatory to use it.


thank you.

Yanuar

 

[bimr]

Tank construction standards are generally independent of and do not consider coating or lining applications..

Venting is required by tank standards such as AWWA. The AWWA Standards are guidelines for best practices. They aren't laws or codes, but they are based on the wisdom and experiences of the best water professionals in the industry. If one did not use the venting, one would be positioning themselves for criminal and civil liabilities.

 

[JStephen]

The tank standards require a fillet weld on the top side of the roof plate.
They allow the purchaser to also specify seal-welding the underside of the laps, which, if done, would generally be for corrosion resistance. The overhead welding is expensive, and so it's an economic issue of whether it should be done or not.

API-650 requires emergency vents (or a frangible roof). API is assuming the products stored are flammable, and in the event that the tank is surrounded by fire, it is desired that the tank not release the product. Where the product is not flammable, this is less of a concern. The standards specifically for water tanks (AWWA D100, etc.) require venting but not emergency venting.

See an example of what you're avoiding here:

https://www.youtube.com/watch?v=6qcrwNM74sg

 

[Syahar1975]

Fillet weld on the top side is a must.

Seal weld underside the roof for painting purpose also required. However, caulking (make sure the product is compatible with the painting material) also acceptable.

I agree the the overhead welding on the roof is expensive. But this should had been considered during the pre-contract stage. When the client specification in tender document specifies "painting underneath the roof" then all related cost due to this requirement must be calculated and included in the project budget.

 

[yanuarsaja]

Hi all, thank you for the input.

The storage tank will be designed as per API 650 not AWWA D100.
refer to your feedback, for the out side, fillet weld is mandatory but for inside, seal weld is sufficient rather than fillet weld. Yes, cost of overhead welding will also be cosidered for this requirement.

Another issue : there is requirement to have two (2) manway/Manhole at Sheel side for Diameter less than 42 m.
i think for small diameter, this requirement is not possible to install two manholes (180 deg apart) due to limited area. DOes any body know, the minimum requirement (diameter) that sufficient to profide two manhole? letsay 10m Dia, 1 manhole is enough.

Thank you for your advice.

Yanuar

 

[MJCronin]

IMHO, there are no hard and fast rules, the number of manways is specified by the tank purchaser. Manways serve as access for men and equipment. When I have asked for tank price quotes, I always request the cost adder for an additional manway from the fabricator.

Manways in the roof serve as vents for access and cleaning. OSHA indirectly requires roof manways

For tanks storing liquids that will require frequent cleaning, I would consider two shell manways as a minimum.

Here is another discussion on this topic:

http://www.ast-forum.com/ast_forum_tree.asp?master=12827

MJCronin
Sr. Process Engineer

 

[yanuarsaja]

HI MJCronin, Thank for the related forum.
Basically, the requirement is clearly state in the specification size of Man Hole shall be 30",and Dia < 42 m shall have 2 Shell Man holes as minimum.

There is challege for small tank, and also for cost point of view,
It means even for small tank let say 3m diameter, 2 man holes is required?

Yanuar

 

[bimr]

For a 3m dia, one 450 mm manhole would suffice.

Weld Joints*: Describe the type of roof plate weld joint, which may be lap joint, butt joint, or some combination thereof.

Seal Weld Underside of Lap Joints? (Yes/No): May be required for roof plates with internal lining or to prevent crevice corrosion.

C.3.2.2 If a lining is applied to the underside of the roof, all joints that will have a lining shall be seal-welded.

https://law.resource.org/pub/us/cfr/ibr/002/api.650.2007.pdf

 

[Syahar1975]

I have never seen in API 650 nor other relevant standards in regards to shell manhole quantity requirement based on tank diameter.

This must be specified by the clients in their project specification.

The tank contractor then generate tank data sheet and this tank data sheet shall be part of the contract technical proposal submitted to the client for tender purpose.

During construction stage if the client request extra manhole then we have the right to ask variation order or extra cost.

I have experienced 6 nos. of 7 M tank diameter with 1-24" shell manhole but during the construction stage the client request another 1-24" shell manhole.

It was very hard negotiation because the cost involved is quite big for 6 tanks. We did installed these additional shell manholes after all commercial aspect was agreed.

 

[yanuarsaja]

HI, thanks again for the sharing.
The ManHoles quantity is writen in project/Client spec depend on the Tank Diameter.
for ex. for dia less than 42 m, the spec request to have 2 Manholes as minimum.
For above requirement, it is still debatable.

 

[MJCronin]

Again yanuarsaja, both the NUMBER and LOCATION (shell and/or roof)of manways must be considered for the specific tank based on the type of liquids stored.

Roof manways are very important for maintenance and cleaning operations, and, in the USA, are important for venting.

Truly, I understand that the customer can often be his own worst enemy !

But following the customer's specification blindly without asking reasonable questions is a sure road to disaster

MJCronin
Sr. Process Engineer

 

[Syahar1975]

MJ Cronin,

Agree with your opinion.

During tender stage we can ask or suggest to the client if we found something unusual or not mandatory required by the code. Because this will affect to project cost and schedule.

I have experience with one of the client where they specified in their project specification that the plumbness of the tank shell is 1/400 not 1/200 as specified by the code. But no body address this issue during pre-contract stage. During the construction we struggled to comply this contractual requirement.

The other client they specified plumbness and roundness must be inspected every shell ring and 3 location on every plate in each ring. Again no body ask this question during pre-contract stage. I still remember how difficult we were during construction.

 

[yanuarsaja]

Hi..
Yes.. Clarification is important to estimste capex,complexity and also sometimes the schedule.
For general spec.. We need clarification for the minimum diameter, and for more detail shall be shown in each individual tank data sheet. As you mention each tank may have different purpose and frequent of cleaning ect. And can affect on number of manholes.

Thabk you McJ for your support
And syahar1975 for the sharing.

Yanuar