Proceedings of IPC2006
6th International Pipeline Conference
September 25-29, 2006, Calgary, Alberta, Canada
Paper IPC 2006-10045
Development of Reliability-Based Design and Assessment Standards for Onshore
Natural Gas Transmission Pipelines
Joe Zhou
TransCanada PipeLines Limited
Calgary, Alberta
Brian Rothwell
TransCanada PipeLines Limited
Calgary, Alberta
Maher Nessim
C-FER Technologies
Edmonton, Alberta
Wenxing Zhou
C-FER Technologies
Edmonton, Alberta
ABSTRACT
Onshore pipelines have traditionally been designed with a
deterministic stress based methodology. The changing
operating environment has however imposed many challenges
to the pipeline industry, including heightened public awareness
of risk, more challenging natural hazards and increased
economic competitiveness. To meet the societal expectation of
pipeline safety and enhance the competitiveness of the pipeline
industry, significant efforts have been spent for the
development of reliability-based design and assessment
(RBDA) methodology. This paper will briefly review the
technology development in the RBDA area and the focus will
be on the progresses in the past years in standard development
within the American Society of Mechanical Engineers (ASME)
and the Canadian Standard Association (CSA) organizations.
approach is intuitive and is simple to apply. Relative to
pressure piping in general, its incorporation in standards goes
back at least to the origins of the ANSI pressure piping code in
the 1920s, and it has been perpetuated in subsequent editions
and reorganizations leading to the current ASME B31.8
standard (ASME, 2003). Separate Canadian pipeline standards
appeared in the late 1960s; they were derived directly from the
contemporary American standards. Though very significant
divergence has occurred in the intervening years, the primary
design approach in the current CSA Standard Z662 (Canadian
Standards Association, 2003) has not changed. Other national
and international standards for onshore pipelines, with limited,
recent exceptions, have also used allowable stress methods.
This approach has generally been successful in delivering
acceptable levels of safety and integrity, and to date has not
greatly hindered the very considerable advances that have been
made in pipeline materials, design and integrity maintenance.
The decisions to use the specified minimum yield strength as
the reference stress, and to apply high-level hydrostatic testing
to justify relatively high utilization factors, together with
dramatic advances in materials technology, have allowed
pressure design stresses to be more than doubled over the last
fifty years, with huge economic benefits. Nevertheless, the
approach suffers from fundamental deficiencies that appear to
be limiting in the pursuit of further advances.
INTRODUCTION
Since the origins of long-distance transportation of
hydrocarbons by pipeline, design has been based on allowable
stress methods. In such methods, for specific design checks,
stresses are limited to some fraction of a conventionallydefined reference stress that notionally represents the “strength”
of the material. The difference between the maximum
allowable stress and the reference stress is perceived as
representing a margin of “safety” against structural failure. For
structural elements that are expected to fail by overload, this
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•
•
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based on ensuring an appropriate level of conservatism against
them; the conservatism required will be dependent on the
severity of the consequences of failure. RBDA makes use of
reliability theory, which takes into account the statistical
variability of all the parameters that influence a specific limit
state (failure mode) and failure mechanism in determining the
probability of failure (“reliability” in this sense is simply 1
minus the probability of failure). The related assessment then
involves comparison between the calculated reliability, for all
failure mechanisms, against a target (minimum) value that is
calibrated to account for the severity of the consequences of
exceeding that limit state.
Most significantly, the design process is only marginally
related to the failure mechanisms that have been observed
historically and that will have to be addressed in future,
long-distance pipelines. Almost all recorded pipeline
incidents have been the result of mechanisms, such as
corrosion, mechanical damage and ground movement, that
receive no explicit consideration in design, and that arise
primarily because of the breakdown of prevention or
mitigation techniques.
Certain failure causes simply cannot be addressed, in any
useful way, using a stress-based approach. Examples are
ground movement resulting from slope failures, seismic
activity and frost heave/thaw settlement.
Heightened levels of integrity threat or potential
consequences of incidents (resulting, for example, from
increased population around the pipeline) are addressed by
arbitrary increases in “safety factor” that generally take no
account of specific pipeline attributes and whose
effectiveness cannot be demonstrated or quantified. The
result is an overall inconsistency in safety and reliability,
with the virtual certainty that some designs are less safe
than we would wish, while others are less economical than
they could be.
There is very little integration between the design and the
operation and maintenance processes, even though pipeline
integrity is critically dependent on both. This renders
extremely problematic the modern design mantra of
“lowest lifetime cost consistent with acceptable lifetime
integrity”.
While the background of this approach is well-established,
its application to onshore pipelines poses a number of
challenges. Research conducted over several decades, and still
on-going, has allowed reasonably-effective limit state functions
to be developed for most of the widely-applicable failure
mechanisms. However, detailed knowledge of the statistical
properties of all the variables involved is limited, since it has
hardly been required at all for traditional design and assessment
practices. Further, it is clear that the establishment of
appropriate and accepted reliability targets is at the core of any
practical application of RBDA; while there are many
precedents in other industries, they are not usually directly
transferable and, in any event, have not been generally
endorsed by the pipeline industry or its regulators.
Collaborative studies begun in the Nineties aimed to assess
the general feasibility of developing RBDA methods for
transportation pipelines, and established that the required
technical knowledge and information was available or could
readily be developed, but that different applications (e.g.
liquid/gas, onshore/offshore) could pose very different
problems. In 2000, BP and TransCanada PipeLines funded
work conducted at C-FER to develop guidelines specific to
onshore gas transmission pipelines, including preliminary
reliability targets, and it is the stream of work that was initiated
by this project that is summarized in the following section.
These deficiencies, which could be critically limiting for
the development of future, long-distance pipeline systems, can
be addressed through the adoption of a reliability-based limit
states approach, which can be applied to both the design of new
pipelines and the evaluation of existing ones. The approach is
thus referred to as “reliability-based design and assessment”
(RBDA). Though its application to onshore pipelines is
relatively recent, it has been widely used in other fields of
engineering, including buildings (Ellingwood et al., 1980;
Bartlett et al., 2003), bridges (MacGregor et at., 1997), nuclear
plants (Hwang et al., 1986), offshore structures (Canadian
Standards Association, 1989) and, more recently, offshore
pipelines (Jiao et al., 1996; ISO, 2001).
SUMMARY OF TECHNICAL DEVELOPMENTS
The work carried out in the course of the project sponsored
by BP and TransCanada PipeLines (Nessim et al., 2002a,
2002b; Zimmerman et al., 2002) developed guidelines for
RBDA of onshore gas pipelines that provide detailed guidance
on the development of models required for the analysis. It
provided models for some specific, important design conditions
and failure causes, including yielding and burst of defect-free
pipe, external interference, corrosion and transverse ground
movement, so that these could be analyzed without further
development. The project also developed software for the
calculation of failure rates related to these causes. An approach
for the establishment of target reliability levels was proposed
that was based on levels of societal and individual safety risk
that could be deemed to be acceptable. This concept was
particularly important in providing a coherent foundation for
The following sections of this paper provide a very brief
background to RBDA methods, including a summary of the
technical developments related to their application to onshore
pipelines; the main emphasis of the remainder of the paper is
on the steps that have been undertaken, and that are continuing,
to incorporate the approach into North American standards for
onshore gas transmission pipelines.
RBDA CONCEPTS
RBDA can be considered as a sub-set of limit states design,
in which all the failure modes and mechanisms that can apply
to a specific pipeline are addressed, and design decisions are
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additional reliability targets based on individual risk, to ensure
that isolated individuals (whether resident or casual presence)
are also protected. The tolerable individual risk levels were
based on published precedent, including guidelines proposed by
MIACC (1995) and HSE (2001) in the U.K.
subsequent standardization efforts, since it was consistent with
a broader realization in many areas of the North American
pipeline industry that questions of public safety could not
rationally be discussed in absolute terms, but needed to invoke
at least relative levels of risk. Since time-dependent failure
mechanisms (such as corrosion) are specifically addressed, and
reliability targets are to be met throughout the pipeline life
cycle, RBDA provides an ideal mechanism to ensure that
design and maintenance practices combine to deliver the
requisite level of safety.
The work carried out in the project just described provided
robust general guidelines for RBDA, together with some
valuable analysis tools. The approaches proposed have been
further developed and refined in a project funded by PRCI
(Nessim et al., 2004; Nessim and Zhou, 2005a, 2005b). This
work resulted in the provision of much more detailed and
comprehensive guidelines, aimed at facilitating the application
of the approach by pipeline practitioners, as well as
considerable refinement of the proposed target reliability levels.
It also included a more detailed analysis of the economic
implications of the RBDA approach, in particular illustrating
the potential which it offers for finding an optimum trade-off
between design and maintenance measures in optimizing
lifetime cost.
The process for developing target reliability levels
proposed in this project is of some interest, since it has been
maintained, though with significant refinements and
improvements, in subsequent work intended to lead to the
adoption of RBDA in standards. It started from the analysis of
the societal risks associated with a comprehensive set of
representative cases of pipelines designed according to ASME
B31.8 and maintained according to current industry best
practices. The failure causes explicitly examined were limited
to corrosion and equipment impact, which together account for
roughly two thirds of the pipeline incidents in North America
and Europe; the total risk was estimated by increasing the sum
of the calculated risks by a factor of 1.5. The consequence
severity was calculated on the basis of an approach developed
by Stephens et al. (2002), which has also been used in the
definition of high-consequence areas in the context of the US
gas pipeline integrity rules and ASME B31.8S (ASME, 2001).
This approach depends on simple, closed-form models that
have nevertheless been shown to give reasonable results when
compared with state-of-the-art computational models. These
simplified consequence models result in a proportional
relationship between the safety consequence and ρPD3, where ρ
is the population density, P the operating pressure and D the
nominal outside diameter of the pipeline. The calculated risk
levels for each design case were combined to determine a
weighted average for the entire set, based on weighting factors
determined from an industry survey of pipeline length as a
function of design parameters and class location. It was
inferred that the resulting average societal risk represented an
acceptable value, since conformance with ASME B31.8 (or
equivalent) criteria is currently seen as de facto evidence of
acceptable design; though isolated failure incidents do occur
that cause public and regulatory concern, they are generally the
result of unforeseen events or a breakdown of management
systems, rather than deficiencies in the design, materials or
planned maintenance activities. It was proposed that this
weighted average societal risk be applied to determine the
target (minimum) reliability, as a function of pipe pressure and
diameter and the surrounding population density. This will lead
to a significant increase in overall safety, as well as to much
greater consistency in the associated risk levels.
The guideline document (Nessim and Zhou, 2005a, 2005b)
lays out the six technical steps in the application of RBDA as
illustrated in Figure 1, and provides detailed guidance on each.
• Identification of relevant limit states: guidance is provided
on the limit states relevant to onshore gas pipelines and the
procedures required to determine their applicability to a
specific situation.
• Development of limit state functions: guidelines for the
selection or development of limit state functions are
provided, and functions are supplied for some of the most
important limit states.
• Development of probabilistic models for basic variables:
the process for the derivation of statistical models of basic
random variables is defined. They can be based on actual
statistical data, theoretical models or engineering
judgment; guidance is provided on model selection, and
relevant statistical data is documented.
• Selection of design parameters and maintenance plan: this
process is largely self-explanatory, but the need for
completeness and the recognition that there may be
constraints, not directly related to reliability, that limit the
available solutions is emphasized.
• Reliability calculation: a detailed methodological guide to
reliability calculation for some of the main limit states
affecting onshore gas pipelines is provided. General
methods are given for single time-independent limit states,
single time-dependent limit states and multiple limit states
(the latter occur when there may be multiple failure
mechanisms from a single causal event or where different
failure modes must be considered for a single failure
mechanism).
• Compare to target reliability: Target reliabilities are
presented for ultimate limit states, leakage limit states and
serviceability limit states, together with guidance on how
Target reliabilities derived from societal risk can become
unacceptably low for small pipelines in relatively unpopulated
areas. As a result, it was considered necessary to develop
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incident, but by the number of fatalities raised to a power
greater than one. Evidently, this criterion will govern when the
expected number of fatalities per incident is greater than 1. The
overall reliability target to be met is then the highest of those
determined according to the three criteria (societal risk with
fixed expectation, societal risk with aversion and individual
risk). The target reliability for ultimate limit states is presented
in Figure 2 and the three risk criteria used for calibration are
clearly reflected in the three straight segments in the target
reliability curve.
they should be applied. The targets for ultimate limit states
(major loss of containment leading to a safety hazard) are
calibrated to risk, as described previously, though the
methodology was considerably refined in the course of this
project (see below). The proposed reliability target for
leakage limit states (which involve only minor safety and
environmental consequences) was determined by a
combination of economic analysis (including the intangible
costs of adverse regulatory response), historical
performance and code calibration. The target for
serviceability limit states, which involve no loss of
containment, is arbitrarily based on values drawn from
other standards; it will rarely take effect, since the
consequences to the operator (cost of repair, service
interruption) will often dictate a higher reliability.
1 - 1E-09
Target Reliability (per km-yr)
1 - 1E-08
1 - 1E-07
SR with
aversion
1 - 1E-06
1 - 1E-05
1 - 1E-04
SR
1 - 1E-03
1 - 1E-02
IR
1 - 1E-01
1 - 1E+00
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
3
3
ρ PD (people/ha-MPa-mm )
Figure 2. Proposed Target Reliability Level for Ultimate
Limit States of Onshore Natural Gas Transmission
Pipelines
Figure 1. Overview of RBDA Process
The target reliability described above was defined in terms
of per km-year. Recognizing the fact that integrity threats to a
pipeline were often located at specific location and reliability
was not uniformly distributed, a reliability evaluation process
was developed that was based on the average reliability over an
characteristic evaluation length. The characteristic evaluation
length was suggested to be 1600 maximum to reflect the
process for determination of the current location classes, based
on which many data used in the target reliability calibration
process were collected. Supplemental study was also conducted
to rationally combine the distributed failure probability (e.g.
contributed by mechanical damage) and the location-specific
failure probability (e.g. contributed by ground movement) in
order to determine the total failure probability. A reliability
evaluation procedure for the combined distributed and location
-specific failure probabilities was summarized in Nessim et al.
(2006).
As has been mentioned, the process for the establishment
of target reliability levels was considerably developed and
refined in the course of this project. For the calibration of
ultimate limit state targets, a matrix of 240 design cases was
analysed, covering five diameters, three operating pressures,
four strength grades and four class locations. Weighting factors
were derived from a survey of approximately 90,000 km of
North American gas transmission pipelines, and representative
population densities from a survey of over 19,000 km of right
of way. The primary reliability targets were based, as described
previously, on the weighted average societal risk, expressed as
the average expected number of fatalities, with an additional
requirement based on individual risk that only takes effect for
low safety consequence levels. It was also noted, however, that
a number of standards, regulations and recommendations
incorporate an aversion function, that is, they try to reflect a
heightened societal aversion to incidents that produce many
casualties. To account for this in the format adopted in the
current work, a third criterion was derived, based on the same
design cases, incorporating the risk aversion implicit in current
ASME designs. This can be captured by expressing the
consequence not as the expected number of fatalities per
An analysis of the design and cost implications of the
RBDA approach, relative to the traditional design process, was
also undertaken. It showed that modest wall thickness
reductions would be possible for most of the Class 1 design
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the items that are required, recommended or permitted, together
with directly related explanatory notes, and a “commentary”
section, which provides deeper background, methodological
assistance and some statistical data.
cases analysed, with the potential for appreciable cost savings.
For the other three classes, as might be expected, there was a
mix of wall thickness increases and reductions, with the
increases applying predominantly to higher grades, smaller
diameters and lower pressures and the reductions relating to
lower grades, larger diameters and higher pressures.
In order to make the material in the later clauses
comprehensible, an overview of the RBDA process is first
provided, following the lines discussed previously. This is
followed by requirements for the classification of limit states as
ultimate limit states (ULS - large leaks and ruptures and other
structural conditions that can progress to lead to major loss of
containment), leakage limit states (LLS – leaks less than 10 mm
that do not constitute a severe safety hazard) or serviceability
limit states (SLS – violation of a design or service requirement
that does not lead to a loss of containment). Requirements for
the determination of the applicable limit states for specific
cases are given, and a listing of potential limit states applicable
to the different stages of the life cycle, together with their
classification (ULS, LLS, SLS, stress or strain criterion, timedependent or -independent), is provided.
The final product of the PRCI-sponsored project was
probably the most important in promoting timely progress
towards standardization. A draft standard was prepared that
was intended to form the basis of development within the key
North American pipeline standards bodies. This document will
be discussed in more detail in the following section.
Technical development is continuing in a number of
different areas, including the consideration of additional limit
states and advancing methods for strain-based limit states,
particularly for higher strength materials, whose less-forgiving
stress-strain behaviour places a premium on accurate limit state
models and realistic material property data. In addition, the
pipeline industry in North America is continuing its effort to
connect natural gas from remote production basins. As a result,
particular attention is required for development of hazard
assessment methodologies, engineering models for stress and
strain prediction and databases that adequately address
discontinuous permafrost, earthquake, and slope movement.
The reliability targets to be met, derived as described in
Section 3 above, are defined, and, for ULS, detailed
requirements are given concerning how they are to be met,
including pipeline segmentation, establishment of an evaluation
length and the calculation of population density. An option is
provided to use nominal population densities corresponding to
the existing four location classes, where site-specific
information is not available. In assessing conformance to the
ULS targets, large leaks are treated as ruptures unless the
failure probability calculation method is capable of
distinguishing between them. If it does make this distinction,
rules are given for combining the two failure modes based on
their relative consequences. A method for dealing with
location-specific limit states (e.g. known corrosion features,
moving slopes) is given. Since the targets for leakage limit
states and serviceability limit states are constant and are not
directly driven by safety concerns, they are dealt with very
briefly. A most important aspect of this part of the document is
the requirement to put in place operational procedures that will
ensure that the specified reliability targets are met throughout
the life of the pipeline, that performance is monitored, and that
adequate records are maintained, communicated and transferred
as needed. These requirements also imply that analyses need to
be revisited in the light of any changes in service conditions or
surrounding land use and of information derived from
operational performance and inspections.
STANDARD DEVELOPMENT
It was considered that, in the course of developing the
guidelines, most of the background information that would be
needed for developing a standard for RBDA of onshore gas
transmission pipelines had been provided. In order to facilitate
comprehension and find support within the standards
committees, a document that reflected the style and the
structural features of a standard needed to be developed. The
main task was to separate the material that would represent the
provisions
of
a
standard (typically
requirements,
recommendations and permissions) from the material that is
purely informative. Informative material that is closely keyed
to the interpretation of the provisions can be captured as notes
to the related clauses; material that provides deeper background
or supporting data is more properly presented in a commentary.
STRUCTURE AND CONTENT OF THE PRELIMINARY
STANDARD DOCUMENT
The document was structured as a stand-alone, nonmandatory Annex or Supplement that, when applied, would
provide alternatives to the related design and operation and
maintenance clauses. The scope is very closely defined, since
it needs to be clear what parts of a pipeline system are covered,
which requirements of the body of the standards are superseded
and which remain in force. A comprehensive listing of the
applicable definitions is an important feature, since many of the
terms used in RBDA have very specific meanings and are not
used anywhere else in the standards. The remainder of the
document is divided into a “provisions” section that contains all
The following clauses deal with the development of limit
state functions for the identified, applicable limit states, the
probabilistic characterization of input variables for reliability
estimation, and the reliability estimation process itself.
The “commentary” section condenses much of the
background and informative material that was already
described. It largely follows the structure of the “provisions”
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of the negative votes generated would compromise rapid
resolution. Accordingly, through the course of the last three
years, several opportunities have been taken to make detailed
presentations to the TC, starting with a presentation of the
overall philosophy and background, moving through the
proposed format and content of the Annex, and proceeding to a
half-day workshop presenting concrete examples of application.
The workshop was particularly beneficial, since it moved
beyond the largely abstract concepts of the Annex itself, and
linked them to concrete examples of practical pipeline system
design and maintenance.
section, providing theoretical background and practical
guidance on most of the topics covered. It also contains limit
state functions that can be used for key limit states that will
need to be addressed for virtually all pipelines (burst of defectfree pipe, equipment impact, corrosion), and provides useful
statistical data concerning loading parameters, mechanical
properties, pipe geometry and defect characteristics. Finally,
there is a comprehensive listing of technical references that
contain additional technical background.
STANDARD DEVELOPMENT IN CSA
The maintenance and updating of CSA Standard Z662, Oil
and Gas Pipeline Systems (Canadian Standards Association,
2003) is the responsibility of the Technical Committee on Oil
and Gas Pipeline Systems and Materials (the TC). The latest
edition of the standard was published in 2003, and the next is
scheduled for 2007. CSA Z662 has contained an Annex
covering Limit States Design since the second edition, in 1996,
but it is not based on reliability concepts. It does, however, lay
some of the groundwork for the limit states design approach.
In 2003, a Task Force reporting to the Sub-Committee on
Design (Design SC) was formed with the aim of preparing
comprehensive material covering RBDA that could be
presented to the TC and balloted for incorporation as an Annex
in the 2007 edition of Z662. The task force took as its starting
point the draft document that had been developed, up to that
point, as part of the PRCI-sponsored project described
previously, and guided its revision and refinement. Coincident
with the formation of the Task Force on RBDA, the Task Force
on Risk Assessment was reconstituted, with the remit of
upgrading the material related to the analysis, assessment and
management of risk. Because of the central role of risk
assessment in the determination of target reliabilities for
RBDA, coordination between the two task forces was
important, and also facilitated the independent benchmarking of
the simplified risk models referred to previously.
This approach has been beneficial in many ways. It
enabled the development of some degree of comfort among the
members of the TC with the basic philosophy of designing and
operating to a minimum reliability limit that depends on the
consequences of failure. On the other hand, it identified
specific areas which could generate some discomfort, such as
the levels of acceptable risk adopted for target reliability
calibration, and provided the opportunity for additional
explanation and clarification that could address some of these
concerns. Perhaps most importantly, it generated a significant
amount of valuable feedback from the TC members, identifying
a number of areas where improvements in content could be
made and where links to other parts of the standard could be
strengthened.
At the present time, the technical content of the document
has been finalized, and it has been edited and formatted to
conform to CSA style. Following discussions with the Design
SC in September 2005 and the TC in December 2005, it was
included in the draft standard that was released for public
review in January 2006. Barring unforeseen problems, it will
be included in the ballot for the next edition, to be voted in July
2006; if approved, it is scheduled to be published in June 2007.
STANDARD DEVELOPMENT IN ASME
Standard development in ASME has followed a parallel
path to that in CSA. The development of ASME B31.8
Standard (ASME, 2003) is the responsibility of the ASME
B31.8 Section Committee (B31.8 SC) under the supervision of
B31 Standard Committee. The latest edition of the ASME
B31.8 Standard was published in 2003 and it did not include
any alternative design methodology based on limit state design
principles. In 2003 a RBDA Task Group (RBDA TG) reporting
to the B31.8 SC was formed to prepare a RBDA standard in the
form of an appendix to the ASME B31.8 Standard. Recognizing
the significant challenge to introduce a new and innovative
approach to the B31.8 SC and the pipeline industry in general,
an extensive communication program was undertaken by the
RBDA TG. As a part of the program, presentations and
discussions were carried out with many industry organizations
including INGAA, API and AGA. The feedback from these
discussions has guided the development of an RBDA standard
in ASME. The technical guidelines developed through the
PRCI project are being used as the basis for standard
development. Special attention is also paid to keep consistency
Though the task force reports directly to the Design SC, an
important feature of the standard development process has been
direct interaction with the TC. RBDA represents a major
change in philosophy, relative to the existing standard
requirements for design and integrity maintenance. Standards
committees have a tendency to be conservative bodies, which,
while quite understandable in terms of their duty to the public,
can lead them to draw great comfort from “tried and tested”
methods and to resist innovation. There can be a perception
that any change that allows, in any case, a reduction in the
notional safety margin should be resisted. On the other hand,
there is an increasing requirement to understand, define and
quantify “safety”, so that reliability-based methods can really
provide the answer to an accepted problem. In any event, if a
concept as novel (for the North American pipeline community)
as RBDA were simply presented for approval on a ballot, it is
unlikely that it would receive consensus approval. Even if it
did, based strictly on the CSA rules for ballots (two thirds
majority of those voting), it is likely that the number and nature
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result, a well-conceived and carefully constructed standard for
RBDA that provides adequate safeguards regarding acceptable
methods, documentation and data requirements, and reflects
appropriate safety and integrity levels, should be acceptable to
the Board. The focus on lifetime integrity should also be an
attractive feature.
On the other hand, arriving at suitable
formats for review of applications and conduct of audits may be
a significant practical issue, since simple “check list”
approaches will no longer be sufficient. However, this issue
would also be raised by any meaningful switch towards goaloriented regulation.
between the Canadian RBDA Standard and the ASME RBDA
Standard, and this is achieved by having the same group of key
people involved in both processes.
With continuing efforts in the last three years and many
presentations and workshops that covered subjects ranged from
basic concepts to practical application examples, the B31.8 SC
is now generally supportive of the development of an RBDA
standard as an alternative design and assessment methodology.
At the present time, the technical contents of the proposed
RBDA standard are near to be finalized by the B31.8 SC and it
has been edited to conform to ASME style. The draft standard
has been balloted by the B31.8 SC in May 2006. While there
were a number of disapprovals and comments, there was little
disagreement on the technical contents. Instead the
disapprovals and comments were focused on how the RBDA
standard can be better integrated into the existing B31.8
standard. In June 2006, B31.8SC developed an overall
framework for B31.8 standard to facilitate the development and
inclusion of alternative design methodologies. Within the
framework, three parallel approaches were envisioned. The
existing B31.8 and B31.8S will continue to be the base standard
for most of applications. The proposed RBDA standard will be
the level-3 approach with most flexibility and complexity and
is expected to be published in the near future as a supplement to
B31.8. B31.8 SC is initiating the development of a level-2
approach to fill the gap, which is intended to be a deterministic
approach based on rational engineering principles.
In the USA, matters are further complicated by the
(intentional) separation between standards development bodies
and regulators. For the most part, US interstate pipeline
regulations exist completely independently of national
standards, and developments within a national standard, such as
ASME B31.8, do not necessarily translate into regulatory
acceptance. Given the sensitive relationship between the
regulators and the pipeline industry in the USA, and with the
guidance from the US industry organizations, the development
of a national standard through ASME B31.8 process was
completely separated from the regulatory acceptance of RBDA
methodology. Given that the RBDA standard development is
well in progress and the RBDA standard is anticipated to be
published in the near future, a program to communicate and
work with regulators in US to gain acceptance is being planned.
CONCLUSIONS
Reliability-based design and assessment is an approach
that has many significant advantages over traditional methods.
• It directly addresses the actual mechanisms that can lead to
failure.
• It integrates design and operation and maintenance to
maintain acceptable lifetime reliability.
• It leads to much more consistent levels of safety and, with
the reliability targets that are proposed, will improve the
overall level of safety in the industry.
• It allows resources to be allocated optimally.
• It provides effective metrics for the assessment of pipeline
safety and integrity performance.
• It provides an approach for the assessment of new
problems and technologies that is consistent with the
framework that has already been developed.
REGULATORY RELATIONSHIPS
Regardless of standardization activities, in order to be
applicable in practice, the RBDA approach requires regulatory
acceptance. Regulatory relationships are rather different
between Canada and the USA, but similar issues arise. In
Canada, the major pipeline regulators participate in the
development of Canadian standards, and are members of the
related committees at all levels. They are an important element
in the membership matrix required by CSA regulations, and
participate in the consensus process. Most adopt a new edition
of Z662 into their regulations quite quickly after its publication.
Nevertheless, in rare cases it occurs that specific provisions of a
standard are approved over the negative vote of a regulatory
member, and that the regulator subsequently makes an
exception of those provisions in adopting the standard. Even in
the absence of such a risk, it is clearly beneficial to involve the
regulators directly in a proposal as innovative as the current
one, so that they will achieve a degree of comfort with the
approach and will be prepared for the major change in the form
and content of applications made under the new provisions.
Accordingly, a series of presentations and workshops was
conducted with the National Energy Board (NEB), to ensure
that a wider spectrum of staff was exposed to the approach and
that potential problems could be identified. In reality, the
RBDA philosophy is entirely consistent with the NEB’s wish to
move from prescriptive towards goal-oriented regulation, and
provides the tools for rational assessment of performance. As a
As a result of continuing development work carried out
over the last few years, the process of incorporating RBDA into
North American standards, and of securing regulatory
acceptance, is well advanced. A major milestone is the
anticipated approval of an RBDA Annex for inclusion in the
2007 edition of CSA Z662; this is expected to be followed
shortly after by the addition of an RBDA Supplement to ASME
B31.8. The most significant practical test in the future will be
the progress of the first application to a major regulator for a
significant pipeline project based on RBDA principles.
7
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ACKNOWLEDGEMENT
The RBDA standard development has received significant
supports from many people and organizations, particularly
PRCI, CSA Z662 committees and ASME B31.8 committee.
The author wish to extend their sincere thanks to all the people
and organizations that supported and contributed to the
development of the RBDA standards.
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