STI SP001 standard for inspection of small tanks



P.E. Myers, National Institute for Storage Tank Management, Tampa, FL, USA


This article covers the development of a relatively new AST standard that addresses inspection for small petroleum tanks. While there are several existing petroleum storage tank inspections standards such as API 653, the standards provide little specific guidance for small field erected or shop built tanks. For the most part there have been no relevant tank standards that appropriately address the need for inspections of these tanks. The problems of using a tank standard that satisfies both regulatory needs as well as corporate needs are discussed in the context of how the standard applies risk management principles to adapt to these two sometimes conflicting interests in an optimised way. This article is intended to make you aware of this new tank inspection and management tool that provides a minimum set of rules to satisfy tank integrity for small tanks.

STI SP001 is truly a state of the art standard that embraces new ideas. Some key concepts which allow it to maintain tank integrity at reasonable cost are:

• Advanced environmental protection
• Risk management principles (often called risk based inspection RBI)
• Fitness for service incorporated

Role of SPCC

While previous editions of STI SP001 existed, it is the 3rd edition that represents the major changes to the standard that virtually make it a new standard. The 3rd edition was driven by the anticipation of the new US SPCC Rule (40 CFR 112).

This Rule is effectively a national regulation that applies to all petroleum facilities and it mandates inspection for tanks as small as 55 gallons. Although standards such as API 653 may be used to inspect any steel tank, regardless of size, attempting to use it for small tanks can result in potential problems. For example, since API 653 is aimed at large tanks it assumes that access to the interior of the tank is possible through manways. Small tanks may not have manways and may not be large enough to safely perform inspections internally. Attempting to adopt API 653 or EEMUA 159 to shop built tanks or to very small field erected tanks would require that each company interprets and writes supplementary rules regarding how to do these small tank inspections.

Development process

Because of the anticipated widespread usage of the standard in the US, the STI followed a process which went beyond the requirements that ANSI has established for accredited standard writing organisations (although STI is not an ANSI accredited organisation). The hallmarks of this process are:

• Balance by stakeholders including regulators, manufacturers, consultants and owners and operators

• Consensus which was accomplished with the voting process

• Open process which allowed anyone in the public or private sector to review the proposed standard and make changes

• Due process which included a methodology for resolving negative ballots on the final standard

Although we do not have time to discuss this process in detail, the ANSI voluntary standards have the best chance of resulting in a standard that is developed with sufficient expertise and consideration of stakeholder positions to allow it to receive buy in by all stakeholders.

The need for a new tank inspection standard

To understand why a new standard was needed it is useful to consider the specific aspects of tank inspection and tank integrity that are not very well addressed by currently available tank inspection standards:

• Risk based inspection
• Leak detection (which relates to risk based inspection)
• Double wall tanks, flat wall tanks, portable containers
• Inspection incentives for well designed tanks with low risk

The more important elements of these items are covered below.

Advanced environmental protection

Although API has defined a release prevention barrier (RPB) in API 2610 (Second Edition, May 2005, para 3.15), it does not show how to use an RPB effectively. STI SP001 actually classifies tanks with RPBs as lower risk and provides reduced inspection levels for these tanks. For example, a shop built tank with a volume of 10,000 gallons that is within a secondary containment area but is in direct contact with the soil is classified as a Category 2 tank (See Table 1). It must be internally inspected every 20 years and externally inspected every 10 years if leak detection is not used. However, the same tank with an RPB moves into category 1. This tank may be externally inspected every 20 years only. No internal inspection is required.

Another unique aspect of Standard SP001 is the incorporation of leak detection as both a requirement and an option. More significantly the standard frames the role of leak detection into the bigger picture considering risk management, different kinds of leak detection, and as a way to reduce internal inspection frequency by applying leak detection. A complete discussion of the role of leak detection is given in Figure A3.5 of the Standard (See Figure 1).

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