Agreed - that is what all the codes appear to say. However, the test would not stress the tank to operating conditions (such as when sg = 1.85).
I saw a reference in an old drawing where they filled the tank with water and then applied a slight internal pneumatic pressure, although so far I have found no reference to such a procedure in the literature. This method would also apply a lift to the underside of the tank roof which may not be advisable.
Wondering if there is any other test procedure stated anywhere else.
Do we have no other issues involved with hydrotesting except Sp Gravity?
and no impact of leftover testing fluid onto tank's integrity etc.if faults witnessed/repairs encountered?
Consider testing by using Barite, sg 4.5, as a dry powder or as a mixed additive to H2O, to meet or exceed the 1.82 sg of molten Sulfur potential fluid pressure on the tank.
A knowledgeable Chemist could possibly recommend other H2O increasing additives.
At 74th year working on IR-One2 PhD from UHK - - -
Admittedly we didn't have such high SG product, but we recently hydrotested some tanks with a standpipe bolted to a top flange, to increase the head seen at the bottom. (Wouldn't work for open top tanks though.)
How tall is the tank? If it's not that tall, the change in pressure due to depth would not be significant compared to the applied pressure. Even so, you could change applied pressure so that final pressure at the bottom is the same (pressure at the top would actually be greater).
API 650 Appendix F includes putting pressure under the fixed roof to 1.25 the design presure. Or course, the roof needs to be designed for the pressure. At least you don't have any issues with brittle fracture due to cold temperatures.
API offers no other guidance, and in fact has recently answered the question "Does API 650 require any additional testing beyond the hydrostatic (water) test specified in Section 5.3.5 for a tank designed for product with specific gravity greater than 1?" with this answer: "No. Section F.7.6 provides addtional requirements for Appendix F tanks. The purchaser may require more stringent testing as a supplemental requirement."
I did some Googling and found that the book "Guide to Storage Tanks and Equipment" by Bob Long & Bob Gardner refers to the European code pr EN14015 which requires a temporary extension to be built for hydrotesting tanks that hold liquids with sg greater than 1. JohnGP's standpipe method would address this requirement with a simple set up.
Also, the book "The Aboveground Steel Storage Tank Handbook" by Digrado and Thorp says that API620, sec 5.2.3, provides two methods for tank hydrotesting combined with an air pressure up to 1.25 times design pressure. This should be similar to what IFRs describes above. However, this method requires a lot more safeguards I am sure.
I plan to check out API 620 and 650 codes soon.
Thanks for all the info everyone.
The idea of a standpipe is just plain dangerous. In order to handle the excess pressure on the roof the shell-to-roof joint must be string enough and the tank must be anchored. So if you have a large tank, you will not be able to afford the total cost. This is an engineering issue that should be addressed by a competent tank consultant.
The solutions using internal pressure, standpipes, heavy liquids, etc., can be done on very small tanks, but they aren't really needed there, either. On a tank of any size, it is impractical to pressurize the roof to achieve significant increases in pressure in the fluid. Purchase and disposal of any other heavier product would be very expensive on a tank of any size as well. If the tank includes a corrosion allowance, it would make it that much harder to stress to the design level. Additionally, when the product is heated, as sulfur, the design conditions can't be duplicated using products at ambient temperatures.
Normally such tanks will be built and hydrotested like any other tank. If additional safety is desired, it would make more sense to specify a lower design stress, a decreased joint effiiciency for design, or increased radiography, rather than going to great lengths to overstress the shell.
The API-650 hydrotest is not intended as an overstress proof-test as is done with pressure vessels. API limits the amount of overstress by specifying the allowable hydrotest stresses, but does not require that these stresses be reached in order to properly hydrotest a tank.
