Surveying the condition of high-pressure gas pipelines is an important part of ensuring their engineering integrity, with intelligent pigging being the preferred option for pipelines of more recent design.
The pipeline network of Open Grid Europe has around 2000 km of lines that are more than 50 years old. The construction of these pipelines reflects the changing state of the art from about 1910 to 1960. These older pipelines were installed in the Ruhr district as part of plans to use the gas generated in coke ovens for long-distance transmission over a wide area and transport it to different consumers, which is why much of this older pipeline stock is to be found in densely populated urban areas. Their very location often prevents general renovation and replacement for a variety of reasons.
Unlike the butt-welded pipe joints in common use today, these older pipes were connected using a variety of spigot-and-socket designs. The specific characteristics of these pipelines rule out the use of intelligent pigs as part of an integrity survey exercise.
The PIA² (Pipeline Integrity Analysis) process has therefore been developed over a period of years to survey the strength of pipelines which cannot be pigged.
As part of the survey, the loadbearing capacity of the spigot-and-socket joint is compared with a potentially existing load. This potential load is compared with the loadbearing capacities of the joints as determined by component tests and FE calculations. Finally, the survey takes into account certain factors of safety in order to make recommendations for where and to what extent further measures are needed.