In the first, Dr Ted Anderson of the Quest Integrity Group based in Boulder, Colorado, United States, looks at advanced assessment of pipeline integrity using ILI data, while in the second, Guy Desjardins – of his eponymous consultancy based in Calgary, Canada – reviews the detection of active corrosion from repeated ILI runs.

Advancing integrity

Advanced assessment of pipeline integrity using ILI data by Dr Ted L Anderson, Quest Integrity Group, Boulder, Colorado, USA.

Dr Anderson points out that the considerable improvements in ILI and computing technology, coupled with the emergence of fitness-for-service standards, have created an opportunity to advance pipeline integrity assessment, and his paper describes novel approaches for assessing cracks, wall loss, and dents in pipelines using data from ILI tools.

Crack-detection ILI tools that rely on shear-wave ultrasonic thickness (UT) measurement have improved significantly in both detection probability and sizing accuracy. The combination of advanced modelling, employing realistic fracture-mechanics’ models that use 3D elastic-plastic finite element analysis, and reliable ILI provides a superior alternative to hydrostatic testing for ensuring pipeline integrity. ILI tools that measure wall loss with compression-wave UT provide superior results compared to magnetic flux leakage (MFL) tools, outputting a ‘digital map’ of individual thickness readings, which is ideally suited to effective area assessment methods such as RSTRENG and the API 579 Level 2 remaining strength factor calculation. Dr Anderson describes how his firm has developed software that can rapidly process large quantities of ILI wall-loss data and evaluate the maximum allowable operation pressure (MAOP) at discrete locations. The ranking of these MAOP values serves as a rational and rapid means for prioritising the severity of corrosion throughout the line.

Dents that are introduced during fabrication, installation, or by a third party are among the most common source of failure in pipelines. Traditional assessments are based on a simplistic characterisation of the dent (for example, the ratio of the dent depth to the pipe diameter), combined with a simple empirical equation. An advanced dent assessment that combines a detailed mapping of the dent from ILI data (either UT or a calliper pig) with 3D elastic-plastic finite element analysis has been developed. This dimensionally accurate 3D model of the dented pipe can be subjected to cyclic loading, and its remaining life can then be computed through a proprietary low-cycle fatigue damage model. Dr Anderson’s paper shows how this advanced methodology can be applied to interacting anomalies such as dent/gouge and dent/crack combinations.

The statistics of in-line inspection

Detection of active corrosion from repeated ILI runs, by Guy Desjardins, Desjardins Integrity, Calgary, Alberta, Canada.

Repeated ILIs of transmission pipelines have been used for many years to estimate corrosion rates, although the calculation of a corrosion rate from a direct comparison of ILI anomalies is often contaminated with ILI measurement errors. Mr Desjardins introduces an alternative procedure for detecting the presence of active corrosion by examining various statistical properties of the data. While the statistics do not estimate the corrosion rate, he points out that they can indicate the presence of active corrosion. Once this has been identified, the operator is then able to address each location appropriately.

Providing strong linepipe

Development and commercialisation of high-strength linepipe, by Hitoshi Asahi, Takuya Hara, Eiji Tsuru, and Hiroshi Morimoto, Nippon Steel Corporation, Futtsu, Japan.

The development and commercialisation of high-strength linepipe is described by authors from Nippon Steel in Japan in a further paper in the Journal.

To meet the increasing worldwide demand, it is becoming necessary to transport gas from remote areas to consumers over longer distances and through large diameter pipelines while keeping the costs as low as possible. The thinner the pipeline wall thickness that can be made by using high-strength steel, the greater the reduction will be in pipeline construction costs. The manufacture of high-strength, large diameter, linepipe made using the UOE process from X100 and X120 steel started toward the end of the 1990s, and has now reached the stage of large-scale testing for practical application and commercial use. At the same time, an ability to accommodate deformation that has not been required for linepipe previously, has recently become a design criterion for pipelines that pass through areas of permafrost, or areas of seismic or other ground-moving activities, and this therefore necessitates the use of strain-based design. This paper reviews the present state of commercialisation and standardisation, the basic pipe production technology, and the properties and laying technology for such high-strength linepipe.

For a cross country pipeline, the linepipe weight linearly decreases with increasing pipe strength, irrespective of the operation pressure and pipe diameter, which is rare for structural steel products. The authors point out that in such a large-scale project, the linepipe cost can be significantly reduced by using a higher strength grade, which will also provide cost savings in both logistics and pipelaying. As a consequence, the development of X100 was initiated partly by Shell’s request to major pipe manufactures in 1994 to see what could be achieved. Subsequently, the development of X120 was the result of a number of joint research projects between ExxonMobil and pipe manufacturers. By 2000, pipe development had advanced and small-scale laying tests and operational trials were being undertaken, in an addition to full-scale gas burst tests. In 2007, X90, X100, and X120 were standardised as ISO3183 and API 5L, and the era of high-strength pipelines is now widely anticipated.

X100 under pressure

Production and development update of X100 for strain-based design applications, by Andreas Liessem, Rene Rueter, and Martin Pant, Europipe GmbH, Muelheim, Germany, and Volker Schwinn, Aktien-Gesellschaft der Dillinger Hüttenwerke, Dillingen, Germany.

Andreas Liessem of Europipe in Germany and his co-authors continue the above theme with their paper on the production and development of X100 for strain-based design application. They echo the important point that the use of high-strength steels is of considerable interest for long-distance gas transmission pipelines as the material promises both economic benefits as well as greater resistance to ground movements and seismic activities. The technology required for such regions necessitates a strain-based design: low Y/T-ratios, adequate uniform elongation, and the shape of the stress-strain curves are of vital importance, and are nowadays at the centre of the efforts for such developments.

Another issue is that the pipes themselves are heated during application of the coating. This factor, in combination with the cold deformation that is needed during manufacture, affects the specific mechanical properties relevant to strain-based design and, as a consequence, recent specifications include test requirements after simulation of coating application.

The authors go on to describe the application of X100 pipe to the 300 km long North Central Corridor pipeline project in Alberta, Canada, for which Europipe manufactured 2.5 km of 42 inch diameter X100 linepipe with 14.3 mm wall thickness. The paper also gives an update of the development status of the material for strain-based design applications.