Pertinent questions (1): are current pipeline design standards adequate?
TWO CURRENTLY RELEVANT QUESTIONS are posed by the authors of the first two papers in this issue: are gas pipeline design standards adequate, and when is a hazard a threat (or a threat a hazard)? The answers to both clearly have an increasing importance to all involved with pipeline operations. Although there are few recorded instances up to now of a pipeline failure due to poor design, in this era of cost-consciousness typified by the frequent and almost-automatic acceptance for the lowest bid for materials and services, today’s designs may well be found lacking in two or three decades’ time in if the correct decisions are not made using the best available science. Distinguishing between a threat and a hazard, however, has a more-immediate application, particularly in terms of the increasing problems of third-party encroachments into pipeline rights-of-way.
Dr Jane Haswell and Peter Boothby start their paper on design standards by looking at the basic pipeline design criteria for onshore gas transmission pipelines with reference to the UK Institution of Gas Engineers and Managers’ (IGEM) TD/1 code Steel pipelines and associated installations for high pressure gas transmission. Amendments incorporated into the recently updated fifth edition of this important document are highlighted, together with appropriate justifications for the adopted changes. The paper goes on to summarise current status of pipe standards and specifications (seen as the practical interpretation of pipeline design criteria), and specific gaps and anomalies that raise cause for concern are highlighted. The issues specific to different pipe types and grades are covered, raising the question: do current pipe standards adequately address the necessary technical requirements, bearing in mind the intended pipeline service application? Areas of concern discussed in detail by reference to specific examples include intrinsic weld geometry concerns in high-frequency welded (HFW) pipe, the absence of a reduction of area requirement for transverse-weld tensile tests, pipeline construction and operation concerns associated with poor weld-bead geometry in spiral pipe, variable flattening test behaviour in HFWpipe, and the supply of multiple alloy types within a single pipe order. Examples of these issues are illustrated in the paper – where appropriate – by photographs taken at the time of pipe production and testing.
As the authors point out, the material, hydrotest, and fatigue requirements for the TD/1 pipeline standard have been developed to reflect improvements in material technology, improvements in material and construction, and increased understanding of defect behaviour and fatigue. Continuing developments mean that TD/1 is a mature pipeline standard which provides practical rules based on UK and international operational experience of the gas pipeline industry. The requirements of TD/1 are provided for the safe design, construction, and operation of pipelines and associated equipment in accordance with current knowledge, and will be subject to periodic review, revision, and updating to ensure that this aim continues to be realised.
Pipeline design standards have undergone continual development and improvement over the years and the recent harmonization of API 5L and ISO 3183 is considered to herald a significant step forward in this respect. However, in order to further ensure the integrity of future high-pressure gas transmission pipelines, the authors consider that the requirements of pipe standards would benefit from the following further restrictions:
(1) The tendency in HFW pipe for hoop strain to be concentrated at the weld seam during (over) pressurization as a result of the absence of weld-metal overmatching, coupled with the localized reduced wall thickness at the weld seam, needs to be carefully monitored.
(2) The acceptance requirement for the cross weld tensile test should include some measure of ductility (for example, minimum percentage reduction of area, or minimum percentage tensile strain), in order to prevent acceptance of tests that simply match the parent pipe grade’s minimum UTS level, but show minimal ductility.
<3> The inclusion of a weld-bead profile requirement for submerged-arc-welded pipe (specifically restricting the minimum permitted weld contact angle at the weld toe) is considered important for high-pressure gas pipelines, particularly where significant pressure cycling during operation may arise, such as for storage pipelines.
(4) The acceptance requirement for flattening tests in the production of HFW pipe should be further tightened to restrict the occurrence of weld-seam breaks.
(4) To prevent alloy variants with multiple chemical compositions being supplied to pipeline project orders, pipe standards for high-pressure gas transmission pipeline applications should include a requirement that – for each pipe size and grade in a given project order – pipe from a single target chemical composition should be used unless agreed in advance.
Pertinent questions (2): when is a hazard a threat?
Guidelines for identifying threats and assessing a pipeline’s susceptibility to those threats in order to select appropriate and effective mitigation, monitoring, and prevention measures – prior to being reactivated – are set out in the second paper. The intention of the authors, from Canada’s National Energy Board, is to provide a generic threat-assessment approach that can be customized to a pipeline’s specific characteristics and conditions, as well as to the regulatory requirements of its own jurisdiction.
A literature review and authors’ experiences across the pipeline industry have identified the need for a generic, yet complete, approach that guides pipeline integrity engineers in the methodologies that adequately and effectively assess threats prior to reactivation, and that can be validated during the operation. This process is becoming more frequent as pipelines face the challenges of ageing, changes in operational conditions, lack of maintenance, and inconsistent integrity practices. Constraints from increasing population density, the higher pressures and flow throughput requirements of a competitive marketplace, and regulatory requirements insisting on higher levels of safety and protection of the environment, are similarly of increasing significance.
The paper considers the following areas, intended to assist in conducting threat assessments:
(1) current regulations and recognized industry standards with respect to reactivating pipelines;
(2) the definition of, and differentiation between, hazard and threat;
hazard-identification analysis for the known and potential situations, events and conditions; and
(3)threat susceptibility and identification analysis process for the known categories derived from the hazard identification process.
As is pointed out, the results from a threat-susceptibility and identification assessment process can help operators, consultants, and regulators to determine the effective inspection, mitigation, prevention. and monitoring measures.
By noting the difference between the words ‘hazard’ and ‘threat’, a process can be used to facilitate flow between the hazard-identification and threat-identification processes, and this is known as threat-susceptibility assessment. During the hazard-identification process, an operator can benefit from procedures such as HAZOPs or ‘what-if’ techniques which can be used to assist in identifying a comprehensive list of possible hazards to a pipeline. During the threat-susceptibility process, the operator can then review each known industry threat and determine whether it has the hazards that give that threat the capability to do harm to the pipeline’s integrity. If a pipeline is – or has been – susceptible to a threat, the operator must conduct a threat-identification process to determine whether the threat actually exists and, if it does, to determine its extent and severity. Further assessment must also be conducted to identify threats and the consequent likelihood of failure, their growth mechanism, and appropriate mitigation.
As the authors emphasize, by determining the susceptibility of its pipeline to a comprehensive list of threats prior to reactivation, the operator stands to gain confidence in itself, as well as in stakeholders and authorities. This is a proactive approach which gives the operator the advantage of foresight which can help to reduce the likelihood of cost-intensive and risky failures.
ScholarOne comes to the Journal
WE ARE PLEASED to announce that the Journal of Pipeline Engineering will shortly implement the widely-respected ScholarOne manuscript-management process for all the papers we publish. As many will know, this is an online system through which authors can upload their manuscripts, and through which the manuscripts and be rapidly and efficiently circulated to our reviewers. Reviewers are able rapidly and straightforwardly to send their comments both to the author and to the editor. The integrity of the system will provide authors with the assurance that their papers are being professionally refereed by a peer group from their own industry. Where necessary, comments and suggestions are sent directly to the author, who can then choose to modify the manuscript accordingly.
Through the use of this system we will achieve our aim of becoming publisher in the Journal of fully-refereed papers, which will provide benefits both to our readers and to our authors, and more widely to the high-pressure transmission pipeline industry as a whole. The Journal, founded ten years ago as the Journal of Pipeline Integrity and reformatted with its current title in 2007, will maintain its position as the only publication for this industry that publishes peer-reviewed papers; we hope that the addition of Thompson Reuter’s ScholarOne system will enhance and improve its reputation and influence.
It is our intention that, by 1 May, prospective authors will be able to submit their manuscripts to us using this system, a link and instructions for which will be found on our site at www.j-pipe-eng.com.