Molten salt storage tank design: limitation of API 650 code 2

[tomapoingo]

Hi everybody,
Question is: how to design a vertical atmospheric tank with an operational temperature of 560°C. The material is SS321H.
Someone suggested me to use API code standard 650 and find information about the material at the operational temperature in ASME code section II part D.

Does someone have experience with the design of atmospheric tanks at high temperature?

BR

 

[lganga]

Did you considered the corrosion problems.?
how did you select the material?

 

[lganga]

Did you considered the corrosion problems.?
how did you select the material?
Luis

 

[tomapoingo]

Corrosion problem have been considered and a 2cm overlay for corrosion have been added.First of all my problem is which code shall I use?

 

[vpl]

Where are you located? Have you asked your local jurisdiction?

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[Duwe6]

tomapoingo, that is exactly the method I would use. And I would plainly document the source of my Allowable Stress on the design drawing and on the calc sheet. Thus either document will answer the question of an API-style tank at 560°C

Make sure that you pick a Design Temp that the operators will not exceede. This tank will be one of the first ones to be audited when regulators arrive at your plant. It needs to be carefully documented, and always operated within the design limitations that you set.

 

[doct9960]

tomapoingo,

I suggest you also post your question to forum809

Is this molten salt storage tank for a solar power plant? The following papers might be an interest to you...

http://prod.sandia.gov/techlib/access-control.cgi/2001/012100.pdf

http://www.osti.gov/bridge/servlets/purl/10189397-0iUhZh/native/10189397.pdf

 

[tomapoingo]

Molten salt tank is for solar power plant. I am italian and there is no italian code to be used.

 

[tomapoingo]

Thank you doct9960 for your fast support but the design of storage tank is made with API650 which has temperature limitations. In the document you sent to me they proceed with API 650 without explaining its limitation. I think the only solution with the actual status of codes, it is to design with API650 and mention the temperature effect on SS321H based on ASME code like duwe6 is suggesting that is the way involved people want to proceed here in Italy.
I wonder whether by proceeding like that the designer could have problems in terms of responsability if something will happen during the operational phase.
Thank you
BR

Vincenzo

 

[jamesl]

API 650 Appendix S is limited to 260 deg C. 560 C is way too high. Thermal expansion is going to be a big problem for such high temperature. I don't think allowable stress is as a big issue as thermal stress is. If the shell is very hot and roof is colder, you are going to see a very high thermal stress at the junction.

 

[doct9960]

tomapoingo,

API 650 is a standard for welded tanks for "oil storage". I am not very familiar with API 650, but I have a gut feeling that the temperature limit was based on the auto-ignition temperature of certain types of oil or petroleum product.

I think the only solution with the actual status of codes, it is to design with API650 and mention the temperature effect on SS321H based on ASME code like duwe6 is suggesting that is the way involved people want to proceed here in Italy.

I would also proceed with this methodology and supplement the design with other analyses (fatigue, thermal stress, FEA, etc.). But take note of what the Foreword in API 650 says. If you do not meet the minimum requirements of API 650 or if you exceed limitations, you cannot reference API 650 on nameplates or Manufacturer's certification. The most important thing is what vpl has said...consult with the local jurisdiction.

I wonder whether by proceeding like that the designer could have problems in terms of responsability if something will happen during the operational phase.

That is why you will need to get the all the required information from the Owner/User, perform the proper analysis, and consult with your jurisdiction to make sure it does not fail. Most of the time, an equipment fails because of the the Owner/User, i.e. specifying incorrect material, operator error, exceeding equipment design limits, or not providing information such as site conditions or pressure/temperature cycles.

The US Department of Energy was able to design an API 650 tank that operated at 565°C. This was for the Solar Two project in the Mojave desert. The plant was just operational for almost 3 years. I believe it was decommissioned because it was not competitive with fossil fuel. More conclusive proof about the tank's design capability could have been achieved if the plant was still operational to this day.

http://www.samsi.info/sites/default/files/Solar.pdf

 

[JStephen]

Very good reference, doct9960.

Tomapoingo, if you'll look through that reference, the facility in question was designed by Bechtel (which is still around) and the tanks were built by PDM, which was bought out by CBI, which is also still around, and also works internationally. And they reference a couple of technical papers or books on the design of the salt equipment. So I think the expertise to design and build the tank is out there.

The use of API-650 gives you standard details, specific materials, design loads, allowable stresses, etc. In this case, though, you may need to supplement standard details anyway. You're using materials not covered by the standard, and allowable stresses must come from elsewhere. Design loads could come from API-650 or ASCE 7-05 or equivalent European building codes. So I don't think it's going to make much difference which standard you start with. You could also use ASME B&PV Code or other vessel codes, applied "to the extent applicable" just as with API-650. In any case, issues such as corrosion, metallurgy, thermal fatigue and detailing for molten salts are not covered by the standards and would require additional investigation.

One other point is that if this tank is fairly small, say, 4 m diameter x 5 m high, the design issues and concerns are much reduced. If it's a huge tank, then it merits much more consideration.

One other thing is that it might be worthwhile to consult the supplier of the salt in question. If they have previously furnished it, or specifically sell it for this purpose, they may also have recommendations on materials and detailing for storage.

 

[racookpe1978]

Equally important, if not more than simply "copying" the details of one standard to a second, very different application simply to be able to say "We met the design standards of XYZ123" (or API or any other "standard" is to develop the design to meet the special criteria of the special situation.

High temperature. High cycling stresses (expansion, contraction) as it operates. If ignition, then burns and secondary failures when the molten salt hits water, air lines, and oil lines or motors and high voltage lines. Transformers? Lube oil? Steam lines? Cooling water?

"Splashing" of molten salt from an elevation above ground? Recovery of the area after the salt solidifies? Corrosion was mentioned above. But crevice cracking? Weld failure? Startup from 0,0 conditions?

You very, very seldom can just copy assumed design solutions and safety margins from one Standard to a different circumstance just to "meet code" and succeed.