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TEAM
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ACOUSTIC
EMISSION TESTING. AN ALTERNATE TO API-653 OUT-OF-SERVICE INSPECTION? The
sales pitch is that you can satisfy the Florida Department of Environmental
Protection (FDEP) Rule 62-762.520(1)(a) with an "In-Service" API-653
inspection coupled with an ACOUSTIC EMISSION (AE) test. Thus you can
avoid the cost of emptying and cleaning a tank to achieve a complete internal
inspection. This simply is not true.
A "baseline", Out-of-Service inspection is a requirement of
FDEP Rule 62-762. The purpose of this baseline inspection is to determine the
internal condition of the tank. and establish a corrosion rate from which a time
interval can be established for the next Out-of-Service inspection. Currently
there is no substitute for emptying the tank and making an internal examination
and tests. The results of anything less may leave you with nothing more than a
"warm cozy feeling". Florida DEP Rule 62-762.520(1)(a) states that all field erected tanks that fall under the rule shall have a baseline internal inspection performed in accordance with API Standard 653, by December 31, 1999. The purpose of this inspection is to determine the internal tank condition and to determine the corrosion rate so that an inspection cycle can be established. This cannot be done without taking the tank out of service. In the December 1994 issue of TTM REVIEW, I wrote an article about tank bottom inspection methods. ACOUSTIC EMISSION (AE) method for determining active leaks is discussed. As indicated in that article, the results of AE testing vary widely on the products stored and contractor ability to correctly perform the test. ACOUSTIC EMISSION (AE) testing cannot be used to accurately determine through-holes in a tank bottom unless they are actually leaking. Many corrosion through-holes are not active leaks. Debris and corrosion product, in many cases have plugged a hole and product is not always leaking. This is especially the case with heavy fuel oils such as grade 5 and grade 6 and bunker C. ACOUSTIC EMISSION (AE) testing cannot be used to determine the corrosion loss or metal condition of the bottom of a storage tank whose bottom is resting on the ground. ACOUSTIC EMISSION (AE) testing cannot be used for flaw detection or metal loss in tank bottoms. Acoustic Emission Flaw Detection requires the plates to be stressed. Since there is no way to induce stress into the tank floor plate, AE method cannot be used to determine the condition of floor plate. ACOUSTIC EMISSION (AE) testing cannot be substituted for an out-of-service "baseline" inspection on an atmospheric aboveground storage tank. This inspection must be performed by qualified inspectors entering the tank and making tests and taking measurements. Beware
of that "warm cozy feeling". If
it seems to good to be true, it probably is.
The main reason for considering AE test methods is to avoid taking the
tank out of service. This would save the time and expensive of product removal,
tank clean-out and disposal. These costs are particularly high with the heavy
fuels such as No. 6 and Bunker C storage tanks, however, at the present time
there is no way to avoid this step in the compliance procedure. |
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