Large tank owners have developed inspection and integrity-testing guidelines: American Petroleum Institute's API 653, "Tank Inspection, Repair, Alteration and Reconstruction." It applies to field-fabricated tanks built to the API 650 construction standard.

Shop-fabricated ASTs typically are manufactured to other standards, such as Underwriter Laboratories' UL 142 or UL 2085. These tanks have smaller capacities, rarely more than 50,000 gal., and, therefore, a lower hydrostatic pressure at the tank bottom. Also, shop-fabricated ASTs are commonly horizontal cylindrical; API 650 tanks are always vertical. The inspection of elevated horizontal tanks markedly differs from that of vertical tanks because the bottom of the tank is visible and, as a result, the tank supports must be checked. Thus, a separate standard for inspection of shop-fabricated ASTs was badly needed.

Consequently, in 2002, the EPA issued a final rule amending the SPCC requirements. The agency prescribed integrity testing and visual inspection for ASTs, both shop-fabricated and field-fabricated, as follows:

"Test each aboveground container for integrity on a regular schedule, and whenever you make material repairs You must combine visual inspection with another testing technique You must keep comparison records In addition, you must frequently inspect the outside of the container for signs of deterioration, discharges or accumulation of oil inside diked areas."

EPA encourages the use of industry standards to comply with the rules. It specifically references STI's SP001-00, "Standard for Inspection of In-Service Shop Fabricated Aboveground Tanks for Storage of Combustible and Flammable Liquids," as one of a number of industry standards that may assist an owner or operator with the integrity-testing and inspection of shop-fabricated tanks. The STI SP001-00 standard includes inspection techniques for single-wall and double-wall shop-fabricated tanks of all types , horizontal cylindrical, vertical and rectangular. It also addresses tanks that rest directly on the ground and those that are elevated on supports. (STI offers a training and certification program for the inspection of shop-fabricated ASTs.)

EPA states that all bulk storage container installations must provide a secondary means of containment for the entire capacity of the largest single container. The secondary means of containment must include sufficient freeboard for precipitation and be impervious to oil. To comply with this requirement, many owners of shop-fabricated tanks have opted for double-wall tanks built to STI or UL standards. EPA has clarified the use of such alternative secondary containment measures (to diking) within a letter that can be accessed on EPA's Web site.

The agency also has revised the applicability of the AST regulation and updated the requirements for various classes of oil and for completing SPCC Plans.

European standards
Developments in Europe bear watching because many tank facility designers and owners have global interests. A common European storage tank standard, EN 12285-1, mandates that all new tanks be double-walled. Closely linked to this standard is EN 13160, "Leak Detection Systems for Tanks and Pipes." That standard describes methods for leak detection, with choice based on risk.

Class I relies on air, either vacuum or pressure, in the interstice. It is considered to be the best system because no product is lost to the environment if a leak occurs. The vacuum approach generally is more expensive. It must provide explosion resistance since vapor can be drawn into the system. The pressure approach, which monitors interstitial pressure and pump performance, can prevent the tank contents from reaching the interstice. However, these pressure systems are designed for European tanks with dished heads; some care is needed to translate the design parameters to U.S.-style flat heads. The vacuum system probably better suits U.S. tanks with flat heads.

Class II involves an interstice filled with an antifreeze mixture and a header tank situated about 3.3 ft. (1 m) above the tank. Change in head of the liquid indicates a leak. Already retrofitted to most UST tanks in Europe, the Class II system is considered to be slightly less "environmentally friendly" because antifreeze can escape if a leak occurs. Also, leak detection failed in some earlier installations when the mixture crystallized. Liquids in use today have been more reliable. However, some countries and individual oil companies are considering banning this method and switching to the Class I system (see below).

 

The European Class I leak-detection system uses vacuum pressure in interstice.
Source: SGB

The new buzzwords

Although codes, regulations, and designs of storage tanks and components continue to evolve, perhaps the most critical issue now is operations and maintenance. As with other hardware, ongoing maintenance and prudent operational practices play key roles in ensuring optimal long-term performance.

Consider, for example, the consequences of water in the system. It can cause myriad problems, from degrading product quality to compromising system integrity. So, operations and maintenance efforts should include a proactive program of monitoring and removing water (Click here for additional information.) Other sensible procedures include periodic tightness testing and inspection of all storage system components , spill buckets, sump boxes, leak detection systems, secondary containment, cathodic protection, system shutdown controls, and so on.

Ensuring maximum component life and functionality should provide sufficient incentives for implementing ongoing system operations and maintenance procedures. However, the regulatory community also is focusing more resources on operational compliance. The EPA is shifting its emphasis from upgrade equipment bean-counting to field inspections, looking for functional compliance of equipment, operations and recordkeeping.

Operations and maintenance are the new buzzwords. The storage tank community cannot emphasize them enough as it strives for ongoing progress in performance and environmental stewardship.

Wayne Geyer is executive vice president of the Steel Tank Institute, Lake Zurich, Ill.