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STI SP001 Standard for Inspection of Aboveground Storage Tanks by mercy2beans112


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

    40 CFR 112

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

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

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

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

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

  American Petroleum Institute
  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”
  API 653 Third Edition, Addendum 2005 “Tank Inspection, Repair, Alteration, and Reconstruction” para
  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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            STI SP001 Standard for Inspection of Aboveground Storage Tanks
                         Phil Myers, PE Chevron Corporation
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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            STI SP001 Standard for Inspection of Aboveground Storage Tanks
                         Phil Myers, PE Chevron Corporation
   •   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

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
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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              STI SP001 Standard for Inspection of Aboveground Storage Tanks
                           Phil Myers, PE Chevron Corporation
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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              STI SP001 Standard for Inspection of Aboveground Storage Tanks
                           Phil Myers, PE Chevron Corporation
                                               Figure L
                                   Release Detection Methods (RDM)

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.

      Leak Testing Method                                                                CRDM
                                                                                   Continuous Release
                                                                                   Detection Methods

                                                                   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
      One-time test for leaks.                                     require sensors or power to operate; releases
      Effective only at time of test                               detected visually)

      Examples                                                                 Examples
      Pressure testing                                                             Double wall tanks
      Vacuum testing                                                               Double bottom tanks
      Helium or chemical marker                                                    Tanks with pans under
      Mass or volumetric leak                                                      them
      testing                                                                      Tanks with RPBs
      Inventory reconciliation                                                     underneath including
                                                                                   under-tank slab
                                                                                   Elevated tanks
                                                                                   Horizontal tanks
                                                                                   Elevated concrete
                                                                                   encased tanks
                                                                                   Tanks on grillage

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