Hi.. I've double wall LPG storage tank (suspended deck at inner tank) sized 44m diameter which had never being internally inspected for 28 years. The inspection group had done the RBI and presented the case, which require the tank to immediately shutdown for internal inspection (of course involved hugh cost & long duration). From design, the tank was designed to API 620 App. R.There are school of practise mentioned that low temp double wall tank is internally free maintenance, not require internal inspection if the temperature maintained at all time subzero (no internal corrosion is expected). As for inspector, there's another risk i.e. crack due to cyclic stress from temperature variation from loading & unloading the product.
The inner tank material is A537 Cl.1 = low temp carbon steel
Design temp (inner) = -30 deg C
Your opinion and sharing is appreciated.
Ladies and Gentlemen,
I am a CWI graduate chemical engineer. My background is petroleum etc. I would be very careful. The organization mentioned
www.api.org is at
202-682-8000
202-962-4797 FAX
techhelp@api.org
. I worked inside of petroleum tanks. I do not know what material of construction we are talking. I would guess nickeled steel. In the 6 o'clock position corrosives tend to do damage. Accessing such without shutting down is not easy. A search of www.spe.org papers info might help. I hope this is helpful.
Sincerely
Len Andersen weld@spemail.org
914-536-7101 , 212-839-6599 8-4 New York Time , 914-237-7689 (H) www.lenandersen.com
Horse sense answer, i.e., not based on standards, specifications and the like but just on common sense.
After 28 years of continuous service, don't you think that the good old tank deserves an internal inspection?
Giovanni S. Crisi
Sao Paulo - Brazil
Hi
I am not sure if the opinion you are asking is about the need for internal inspection, or are you looking for an alternative inspection method? If it is about the need for inspection, then I can only say that we (on this forum) could not possibly know as much about this vessel as the people that performed the RBI study. They obviously had a basis for their recomendation.
Regards
Niekie
Was this tank allowed to come up to ambient temperature?
There are things other than product side corrosion that can cause issues with tanks. Settlement, mechanical damage, cracks, corrosion to the outside shell, tank floor soil side corrosion are a few. API 620 tanks are closer to pressure vessels than tanks, but they have a lot on common with atmospheric API 650 tanks.
You are going to need a 510 and a 653 to do a complete inspection. There is a lot of work to do on a inspecton of these tanks. Talk to a tank inspection company about your issues. Unless you have someone on the RBI team that has a lot of experience with 620 and 650 tanks, you are going to need outside help.
Topic Welding Industry / Technical Discussions / Low Temp double wall tank internal inspection - required?
