Published in 2015, the Pipeline and Riser Loss of Containment (PARLOC) report is the preferred source of risk assessment data for generic loss-of-containment frequencies for offshore oil or gas pipelines and risers. This revision updates the previous report, PARLOC 2001, and presents data gathered for incidents that occurred on pipelines and risers on the UK Continental Shelf (UKCS) during the 12-year period 2001-2012. The report is unique as it provides the only source of such data.
The data in this important study have been collected from leak incidents reported by the 23 pipeline operators involved to the UK’s Health and Safety Executive (HSE) and the Department of Energy and Climate Change (DECC), as well as from a questionnaire survey of the operators.
Data on the population of pipelines and risers on the UKCS have been compiled from two main sources: a commercial pipelines database developed by Infield Systems Ltd and a database compiled by Oil & Gas UK. The former has been used as the basis of the estimated populations of steel and flexible pipelines, while the latter has been used as the basis of the population of control umbilicals on the UKCS.
The report presents failure-frequency statistics for generic types of offshore pipeline and control umbilical. In order for the estimated failure rates to be meaningful, considerable efforts have been made to ensure that the records of failures and the pipeline population, which are the basis of the analysis, are complete and accurate, although inevitably there are some provisos involved.
The report shows that average loss-of-containment frequencies for steel and flexible pipelines and risers has remained almost unchanged in the 12-year period between the first study, in 2001, and the current one.
In an interview at the time of publication last year, Brian Bain, one of the report’s authors, pointed out that “The fact that the two studies reached broadly similar conclusions gives some reassurance in the validity of each. This is reassuring, considering that the expectation may have been that frequencies would increase as infrastructure aged. This shows that safety levels have been consistent and maintained.”
The report gives a great amount of detail and background information which can only be very broadly summarised here. It shows that in the period examined, there were 148 loss-of-containment incidents in the offshore geographic region concerned involving steel or flexible pipelines. These are split into 135 on operating pipelines, four during commissioning or testing, and nine during pipe removal.
For the operating category, 85 incidents concerned steel pipelines and 50 concerned flexibles; for the commissioning and testing category, there were two each for steel and flexible lines; and for the removal category, there were seven steel line incidents and two flexible line incidents. The predominant cause of a loss-of-containment incident for steel pipelines is corrosion; however, for flexibles, there is a wide range of causes and none predominate.
Flexible risers, joining rigid steel pipelines on the seabed to floating production platforms of one type or another, are highly critical components in an offshore pipeline network, and – by the very virtue of their flexibility – are less easily inspected than their rigid counterparts. Their continuing integrity is consequently less easily assured, and this is increasingly recognised as an issue that needs expertise and investment in technology.
As can be seen in an announcement on page XX of this issue, Pipelines International is pleased to be supporting the first conference on flexible riser integrity management, being held in São Paulo, Brazil on 23-25 August.
This issue also contains two important articles on the subject: authors from MACAW Engineering describe how they are meeting the current challenge for operators to develop and implement robust and cost-effective integrity-management strategies to maximise the value of these critical assets (page XX); while authors from the Rosen Group give a case study of how a flexible risers can be inspected using a modified ILI tool.
As part of the modifications involved in this case study, the magnetic-flux-leakage (MFL) tool was fitted with polyurethane-layered support wheels on the magnetizer unit, odometer wheels with an added polyurethane layer, and special MFL sensors featuring a ceramic housing.
The authors point out that while traversing a flexible riser is not a problem for an MFL inspection tool, inspecting the wall thickness of a flexible riser using MFL is not possible because the internal stainless steel carcass comprises an unmagnetisable interlocking layer. However, some of the most-common inner-carcass defect scenarios can be inspected via ILI using tools such as the one described.