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STI SP001 Standard for Inspection of Aboveground Storage Tanks Phil Myers, PE Chevron Corporation

3/16/2006 1

Abstract This article covers why a relatively new aboveground storage tank (AST) standard has emerged and considers its role in the arena of existing AST standards such as API 653, API 12R1, EEMUA 159 and others. First, it should be known that this new standard, STI SP001 was specifically aimed at inspection of small petroleum tanks, whereas the aforementioned standards have been aimed at large tanks or specific industry sectors such as upstream petroleum tanks. The existing slate of standards provided 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 small tanks. Some of the issues that are addressed by this article include meeting regulatory needs, risk management, and the needs of the owner or user. In addition, 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 the need to maintain the mechanical integrity for small tanks. Role of SPCC While previous editions of STI SP001 existed, it is the 3rd edition that is virtually a new standard. The 3rd edition was primarily driven by the anticipation of the new U.S. Spill Prevention Control and Countermeasure (SPCC) rule1. 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 and that internal inspections are always advisable. However, small tanks may not have manways. In addition, small tanks may not be large enough to safely enter to perform inspections. Furthermore, in many cases for small tanks there is no benefit for an internal inspection. Attempting to adopt API 653 or EEMUA 159 to shop-built tanks or to very small field-erected tanks would require that each company interpret and write supplementary rules regarding how to do these small tank inspections or to start from scratch and write specific rules related to small tanks. Clearly it would be preferable to have an industry group (such as Steel Tank Institute) to use a legitimate and recognized standards development process to write a small tank standard which would then be accepted by the regulatory sector to fulfill compliance. In fact, this is how STI SP001 was developed. Development Process Because of the anticipated widespread usage of the standard in the United States, STI followed a process aligned with the ANSI standards development process.The hallmarks of this process are:

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

• Consensus that 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

1 40 CFR 112


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• 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 an RPB (release prevention barrier) in API 26102, it does not show how to use an RPB effectively. While this description varies slightly from the definition in STI SP001, the concepts are similar. API 650 Appendix J specifies the construction of RPBs but does not cover when or how they should be used. In contrast, 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 becomes a lower risk “Category 1” tank. This tank may be externally inspected every 20 years. 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) Risk Management Principles Risk assessment more and more frequently appears in the buzz words used by the industry today, but it means different things to different people (as can be verified simply by asking those around you for a definition). Another buzz word used by the petroleum

2 API 2610 Second Edition, May 2005 Design, Construction, Operation, Maintenance, and Inspection of Terminal and Tank Faculties, para 3.15


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industry and particularly with the API3 member company people, is “Risk-Based Inspection (RBI)”. I like to classify all of these things as risk management whose concept can succinctly be stated to maximize benefits while minimizing costs, given a set of alternatives. There are many fine texts4 that show how risk management is a relatively new technology with many complexities. However, if we look to API for initial guidance, the bottom line is that we minimize the inspection costs by focusing the inspections at the highest risk and most vulnerable equipment (hence RBI). This technology is detailed in API 580 and API 581. API 653 briefly discusses and allows for risk management5. It does this by allowing the owner-operator to “establish the internal inspection interval using risk-based inspection procedures.” However, it does not really provide any details about how to apply risk management. Appendix 1 of this paper gives an excerpt from developing tank regulations in Alaska that provide the rationale behind the state’s unwillingness to accept RBI. Another problem with actually implementing RBI for tanks is that it can be very complex and difficult to achieve. API 581 has a “tank module” that performs tank RBI and there are other API efforts to draft effective risk management principles for tanks. These tools generally require a significant amount of input and skill to arrive at an “answer.” In fact many have claimed that these systems are “too difficult and complex for us to do.” The “acceptability (of risk management) relates to whether risk assessment is understandable and compatible with the attitudes and perceptions of potential users, especially decision makers and the public.” 6 Remember, however, that there are many ways and methods of performing risk assessment and risk management. The methods just described are one approach. Another approach to risk management is what I call a “simplified prescriptive risk management approach.” It is this approach which we used in the development of STI SP001. This can be illustrated by a careful examination of Table 5.5 (shown below as Table 1) of STI SP001 which shows that the principle of RBI is embedded prescriptively into the table. Tanks with a higher level of integrity are given a credit in terms of the inspection frequency and intensity. The highest level is called Category 1. Tanks with correspondingly higher inherent risk are assigned to Categories 2 and 3. Category 1 tanks have a CRDM (continuous release detection method) which includes RPBs, elevated tanks, tanks on grillage, double-bottom tanks or tanks with full concrete slabs under them. Category 2 tanks have secondary containment, but no CRDM, and include single-wall tanks in an earthen dike. A leak in the bottom of a Category 2 tank would not be readily apparent in a walk-around type inspection. Category 3 is the highest risk category and is the same as Category 2, but these tanks do not have spill control or 3 American Petroleum Institute 4 Vincent T. Covello, Miley W. Merkhofer, “Risk Assessment Methods – Approaches for Assessing Health and Environmental Risk” and Center for Chemical process Safety of the American institute of Chemical Engineers “Tools for Making Acute Risk Decisions” 5 API 653 Third Edition, Addendum 2005 “Tank Inspection, Repair, Alteration, and Reconstruction” para 6.4.3. 6 Vincent T. Covello, Miley W. Merkhofer, “Risk Assessment Methods – Approaches for Assessing Health and Environmental Risk” pp264 copywrite 1993 Plenum Press


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secondary containment. Because this approach is generic in nature in that it prescriptively metes out risk management in a table format, the benefit is simplicity and ease of use. However, for this to work, there must be consensus on classes of conditions that constitute higher or lower levels of risk (i.e., Category 1 tanks are lower risk than Category 2 tanks). As a tangible example of how the committee considered a prescriptive risk-based approach to managing safety risks associated with tank entry for inspections, let us look at the need for internal inspections. While the STI committee felt that internal inspections yield the best possible inspections, the risks of personnel entry were also considered equally if not more important than the inspection results. In addition, many of the tanks within the scope of the standard simply do not have manways. The risks of creating manways were weighed against the benefits of an improved inspection and the increase in fatalities as a result of internal inspections. These considerations in part resulted in the division of Table 5.5 into size ranges. It is only when tanks are over 30,000 gallons that an internal inspection is mandatory. The approach used by STI is that simplicity and enforceability are maximized, while tweaking risk based on site-specific conditions is minimized. Each risk management system (as contrasted above in the API and STI examples) is not to say that one is better than the other, but that one may be more appropriate than the other, given the specific users, the decision makers, and socioeconomic factors that impinge on tank integrity. Brittle Fracture While brittle fracture is only addressed in the field-erected tank appendix to the standard, it applies to all tanks – both shop and field-erected – within the scope of the standard. Since these tanks all have shell thicknesses less than ½-inch thick, previous studies show that there is no need for a brittle fracture assessment. The standard eliminates the need for the inspector to obtain a copy of the brittle fracture assessment charts in either API 653 or API 579 to go through an analysis only to find out that the tank wall thickness eliminates the need for such an analysis and the documentation to go along with it. Field-Erected Tank Appendix One of the most controversial aspects during the development of this standard involved the inclusion of small field-erected tanks. The scope includes field-erected tanks up to 30 feet in diameter to a maximum height of 50 feet. The reasons that the committee chose to include field-erected tanks are as follows:

• Small field-erected tanks do not require the brittle fracture assessment that is outlined in API 653

• The thickness of small field-erected tanks is not governed by hoop stress, but rather by constructability, as it is for shop-fabricated tanks

• Many facilities have both shop- and field-erected tanks that are all less than 30 feet in diameter. Rather than inspecting these facilities to several different tank inspection standards, STI SP001 may be used to inspect all of these tanks. This reduces the administrative and contractual burden in that only one inspection agency is required to inspect all the tanks at the facility.


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• Small tanks less than 30 feet in diameter can apply leak detection with a reasonably small threshold so that leak detection becomes a viable tool for verifying tank integrity. This provides an option to the internal inspection intervals of API 653.

• In many cases, it is difficult to determine whether a tank is actually a field-erected or shop-built tank.

There was some concern that the knowledge and skills of the STI inspector might be less than needed for field-erected tanks, given that historically STI inspectors only inspected shop-fabricated tanks. While this argument could be called accurate if assessed now, STI is providing the knowledge and skills through training and testing in future tank inspector certification programs. Every new program needs some time before it becomes established. Summary and Conclusions The 3rd edition of STI SP001 provides the industry with a needed standard that is aimed at shop-fabricated and small field-erected tanks. It incorporates risk-based inspection considerations that tie the intensity and frequency of the inspections to the risks of different types of tank configurations in a way that no other standard has yet done. Also, it incorporates the principles of fitness for service, as in the case of brittle fracture assessments. This standard represents the latest thinking that considers benefits and costs so that it can be bought into by both industry and regulatory stakeholders. Appendix 1 Department of Environmental Conservation Division of Spill Prevention & Response Contingency Plan Regulation Project, Phase 2 Oil Discharge Prevention Regulations Discussion Summary & Draft Regulatory Language September 27, 2005 1) The provisions of 6.4.3 (RBI) are not written in a manner which would make them suitable for use as a regulatory document. Many of the provisions are optional and non-binding; "should" and "can" are used where "shall" would be more appropriate. 2) No professional certification for personnel conducting RBI is required under 6.4.3. The only requirements are as follows: "It is essential that all RBI assessments be conducted by trained, qualified individuals knowledgeable in RBI methodology and knowledgeable and experienced in tank foundation design, construction, and corrosion." The lack of specific requirements makes this section effectively unenforceable. Note that RBI is not strictly defined in API 653, either in Section 6.4.3 or in Section 3 (Definitions). 3) Section 6.4.3 does not reference any industry standards or recommended practices relating to RBI methodology. Even API's own applicable publications are not mentioned, e. g. API RP 579, Fitness-For-Service Assessment, API RP 580, Risk-Based Inspection, and API Publication 581, Risk-Based Inspection Base Resource Document.


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4) RBI is not mentioned anywhere in API Standard 653 except for Section 6.4.3. This short section thus stands alone, and as such is clearly inadequate for the implementation of a complex inspection regime like RBI. Alaska Department of Environmental Conservation (ADEC) does not feel that Section 6.4.3 offers a suitable regulatory framework for the application of RBI principles to the determination of internal inspection intervals. ADEC does not object to RBI in principle; only to the framework provided by 6.4.3. Owners and operators of regulated facilities have the option of developing their own tank inspection protocol, which may include RBI elements, and applying to ADEC for a waiver of 18 AAC 75.065(a). Table 1

Table 5.5 Example tank types and AST Category

Tank Description Tank has CRDM AST Category

AST in contact with soil no 2 or 3

Elevated tank with no part of container in contact with soil yes 1

Vertical tank with RPB yes 1

Vertical tank with double bottom yes 1

Vertical tank with RPB under tank yes 1

Vertical tank in direct contact with soil no 2 or 3

Double-wall tank yes 1

AST with secondary containment dike yes 1


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FIGURE 1 – ROLE OF LEAK DETECTION IN TANK INTEGRITY

Figure LRelease Detection Methods (RDM)

LTMLeak Testing Method

ExamplesDouble wall tanksDouble bottom tanksTanks with pans under themTanks with RPBs underneath including under-tank slab foundationsElevated tanksHorizontal tanksElevated concrete encased tanksTanks on grillage

ExamplesPressure testingVacuum testingHelium or chemical markerMass or volumetric leak testingInventory reconciliation

One-time test for leaks. Effective only at time of test

Industry standards practices such as tank inspection standards are the primary defense against leaks. Standards form the foundation of risk reduction. The applicable standards apply from “cradle to grave” including those aimed at construction, inspection, maintenance, and operations. Applying the addition of the leak testing and release detection systems shown in the boxes below allows maintaining even higher container integrity by addition of leak testing and detection. In addition, the use of leak testing and detection can be used to substitute or supplement for conventional inspection practices.

Release detection is inherent n the design and is considered one of the most robust of leak detection systems. It is continuous and passive (does not require sensors or power to operate; releases detected visually)

CRDMContinuous Release Detection Methods

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