SP001 Standard for Inspection of Aboveground Storage Tanks



Dana Schmidt, Project Engineer, Steel Tank Institute, Illinois, USA


In 1973, the United States Environmental Protection Agency (USEPA) first promulgated the Federal Clean Water Act as 40 CFR 112. The Clean Water Act requires that facilities covered under the USEPA’s SPCC regulations develop and submit a “Spill Prevention, Control and Countermeasure (SPCC) Plan” that is certified by a professional engineer. The purpose of this regulatio is to prevent the discharge of oil into the United States navigable waters. Because the SPCC Rule includes facilities which may discharge oil into groundwater or storm run-off which in turn may flow into navigable waters, nearly all facilities that store or use oil products are affected.

Each year about 14,000 oil spills are reported. It is estimated that there are 400,000 facilities that are regulated under the SPCC Rule, with many not having SPCC Plans prepared.

Revisions to the SPCC Rule were proposed in 1991, 1993, and 1997 and were incorporated into the Final Rule that became effective on August 16, 2002. The full SPCC rule can be found at http://www.epa.gov/oilspill/pdfs/0703_40cfr112.pdf.

Extensions of deadlines have followed the promulgation of the Final Rule. Now, facilities must amend an existing SPCC Plan by February 17, 2006, and must implement it by August 18, 2006. Affected facilities that start operations between August 16, 2002 and August 18, 2006, must prepare and implement an SPCC Plan by August 18, 2006. Affected facilities that become operational after August 18, 2006 must prepare and implement an SPCC Plan before starting operations.

Among the changes are the following:

• Facilities with an aggregate capacity of 1,320 gallons in containers 55 gallons and larger are required to prepare SPCC Plans.

• Storage containers must be tested for integrity on a regular schedule.

Per the preamble to 40 CFR 112: “Integrity testing is any means to measure the strength (structural soundness) of the container shell, bottom, and/or floor to contain oil and may include leak testing to determine whether the container will discharge oil. It includes, but is not limited to, testing foundations and supports of containers. Its scope encompasses both the inside and outside of the container. It also includes frequent observation of the outside of the container for signs of deterioration, leaks, or accumulation of oil inside diked areas. Integrity testing must be conducted according to industry standards.”

Further, 40 CRF 112 states: “Industry standards that may assist an owner or operator with integrity testing include: (1) American Petroleum Institute (API) Standard 653, ‘‘Tank Inspection, Repair, Alteration, and Reconstruction’’; (2) API Recommended Practice 575, ‘‘Inspection of Atmospheric and Low-Pressure Tanks;’’ and, (3) Steel Tank Institute (STI) Standard SP001–00, ‘‘Standard for Inspection of In-Service Shop Fabricated Aboveground Tanks for Storage of Combustible and Flammable Liquids.”

Prior to the issuance of STI Standard SP001, only the API Standard, API 653, “Tank Inspection, Repair, Alteration and Reconstruction,” addressed inspection of aboveground storage tanks for flammable and combustible fluids. The emphasis of this API 653 Standard is the large, field fabricated tanks that are fabricated to the API Standard, API 650, “Welded Steel Tanks for Oil Storage.”

The extensive inspection requirements of API 653 are needed for large tanks because of the large volumes and pressures encountered. API 650 includes equations for calculating the steel thickness needed for a particular tank. These equations take into account the pressure encountered, the type of steel used, the weld joints used, and the weld inspection testing used.

The construction and installation of the smaller shop-fabricated tanks differs greatly from these large, field-fabricated tanks. Shop fabricated tanks are commonly manufactured to other standards, such as UL 142 or UL 2085. These Underwriters Laboratories standards include tables that specify the steel thickness based on tank diameter and capacity.

Shop fabricated tanks have smaller capacities and therefore smaller hydrostatic pressures are encountered at the tank bottom. These tanks are manufactured in controlled shop environments and the capacity is typically up to 50,000 gallons. In addition, shop fabricated tanks are commonly horizontal cylindrical. API 650 tanks are strictly vertical tanks which rest on the ground. The inspection of horizontal cylindrical tanks, as well as elevated vertical tanks, includes very different requirements. The inspection of these tanks differ because the bottom of the tank is visible, and as a result, the tank supports must be inspected. Thus, a standard for inspection of shop fabricated tanks was needed. The SP001 Standard includes inspection techniques for all types of shop-fabricated tanks, including those which are horizontal cylindrical, vertical, and rectangular. Also included are tanks that rest directly on the ground, tanks that are elevated on supports, and tanks that are single or double wall.

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