Inspectioneering Journal

Tank Inspections per STI SP001 5th Edition

By Dana Schmidt, Standards Engineer at STI/SPFA. This article appears in the July/August 2013 issue of Inspectioneering Journal.

Tank inspectors and owners, did you know?

  • Each year about 14,000 oil spills are reported, according to the EPA website.
  • It is estimated that there are 618,000 facilities that are regulated under EPA SPCC in the United States.
  • There are more regulated aboveground storage tanks than underground storage tanks in the United States.
  • Tanks under 300,000 gallons represent 90% of the actual tank units in operation.
  • STI estimates that as many as 4 million shop-fabricated oil storage tanks have been produced since the mid-1960’s. It is difficult to assess how many of these tanks are still in use today, but anecdotal evidence suggests that tanks are often used for 40 years or more.

It is no wonder that the Steel Tank Institute/Steel Plate Fabricators Association (STI/SPFA) continually reviews and updates standards, researches new technologies, and provides education and information to the public and industry professionals. STI/SPFA is a trade association representing fabricators of steel construction products and their suppliers. Member companies produce steel storage tanks, field erected water tanks, pressure vessels and heat exchangers, and pipe and pipelines. Their customers are from the petrochemical, power generation, food, pharmaceutical, fuels, wastewater and water transmission industries.


The U. S. Environmental Protection Agency (EPA) originally promulgated the Spill Prevention, Control, and Countermeasure (SPCC) Rule in 1973, requiring certain non-transportation related facilities to develop and implement an SPCC Plan. The purpose of the SPCC regulation is to prevent the discharge of oil into U.S. navigable waters. A facility’s SPCC Plan describes the preventive measures established so that a spill at the facility is contained. It also describes countermeasures in the event of a spill to prevent the spill from reaching navigable waters. A facility must have a Spill Plan, certified by a licensed Professional Engineer, if it has an aboveground oil storage capacity greater than 1,320 gallons or a buried underground oil storage capacity greater than 42,000 gallons.

After several interim modifications, the EPA formally amended the SPCC Rule to make it largely performance-based in 2002. The EPA then issued the Final Revised SPCC Rule regarding the storage and handling of oils, both petroleum and non-petroleum (40 CFR Part 112).

  • Facilities affected: This Rule has bearing on a multitude of facilities that store oil in containers of many constructions and sizes. Facilities affected are those with total aboveground (i.e. not completely buried) oil storage capacity greater than 1,320 gallons. Containers of oil, petroleum and non-petroleum, of 55 or more gallons are to be included when determining the total oil storage capacity at a facility. Prior to 2002, the smallest container considered for inclusion in the total oil storage at a facility was 660 gallons (Refer to further requirements on the type of tank installations, such as partially buried tanks, found in §112.1 of 40 CFR Part 112).
  • Integrity testing: In §112.8(c)(6) [petroleum oils] and §112.12(c)(6) [non-petroleum oils], the Rule states,

“Test or inspect each aboveground container for integrity on a regular schedule and whenever you make material repairs. You must determine, in accordance with industry standards, the appropriate qualifications for personnel performing tests and inspections; and the frequency and type of testing and inspections which take into account container size, configuration, and design (such as containers that are shop-built, field-erected, skid-mounted, elevated, equipped with a liner, double-walled, or partially buried). Examples of these integrity tests include, but are not limited to: visual inspection, hydrostatic testing, radiographic testing, ultrasonic testing, acoustic emissions testing, or other systems of non-destructive testing. You must keep comparison records and you must also inspect the container's supports and foundations. In addition, you must frequently inspect the outside of the container for signs of deterioration, discharges, or accumulation of oil inside diked areas. Records of inspections and tests kept under usual and customary business practices satisfy the recordkeeping requirements of this paragraph.”

Note that the original SPCC Rule (dating from 1973) did not mandate integrity testing, but rather stated that tanks should undergo periodic integrity testing. This means that, historically, a large number of facilities may not have had a tank inspection program, but as of 2002, they are now required to have one.

Implementation of the Rule’s 2002 amendment was delayed and altered several times. The Final SPCC Rule was published in November 2009, with compliance dates for most facilities to prepare (or amend, if applicable) and implement a Spill Plan no later than November 10, 2010.

Importance of Industry Standards

Prior to 2000, only the American Petroleum Institute (API) Standard 653, “Tank Inspection, Repair, Alteration, and Reconstruction,” included requirements for the inspection of aboveground storage tanks. The focus of API 653 is large, field-erected tanks built to API Standard 650, “Welded Steel Tanks for Oil Storage." API 650 includes equations for calculating the steel thickness needed for a particular tank. These equations take into account pressure encountered, the type of steel and weld joints used, and the weld inspection testing employed. Extensive inspection requirements are included in API 653 because of the large volumes and hydrostatic pressures encountered in these larger tanks.

STI/SPFA developed its first edition of Standard SP001 in 2000. With the support of the EPA, STI/SPFA used a consensus process to further modify SP001. The committee that developed the 3rd Edition and subsequent editions of SP001 included representatives from major oil companies, petroleum marketers, federal and state regulating agencies, tank fabricators, inspectors, and tank equipment suppliers.

SP001 includes inspection requirements for welded metal, shop-fabricated and small field-erected tanks. Also included is the inspection of smaller, portable containers such as 55-gallon drums, intermediate bulk containers (IBCs), and other such containers that may be of metal or plastic construction.

The construction and installation of smaller, shop-fabricated tanks differs greatly from that needed for large, field-fabricated tanks. The shop-fabricated tanks covered by STI SP001 are commonly manufactured to third-party standards, such as UL 142 or UL 2085. These Underwriters Laboratories standards use tables, rather than equations, to specify steel thickness based on tank diameter and capacity. Shop-fabricated tank capacity is rarely more than 50,000 gallons, and this smaller capacity means a lower hydrostatic pressure encountered at the tank bottom. Further, whereas API 650 tanks are always vertical, shop-fabricated tanks can also be horizontal cylindrical or rectangular. The bottom of the horizontal cylindrical tank is visible, and the tank supports used to elevate the tank must be inspected.

Small, portable containers are also included in the scope of SP001, as the inspection of these is not covered by another inspection standard.

Small, field-erected tanks with a maximum shell height of 50 feet and a maximum diameter of 30 feet are also included in the scope of SP001. Many facilities include a mix of tank types (see Figure 1) and inclusion of these tanks allows inspection of sites with a variety of tank sizes by a single inspector.


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Posted by Khan Amir Younus Kamal on October 27, 2015
Please clarify whether this standard also governs... Log in or register to read the rest of this comment.

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