Other scenarios that could cause integrity concerns are: ) Third party: This is more a concern in shallower waters
and can be the result of trawl/anchor damage to a pipeline. ) Mechanical: These can be related to the manufacturing or
installation process of the pipeline. ) Natural hazards: Wave action and currents can cause
scouring and accentuate free span issues. Although pipelines are designed and manufactured in accordance with design codes, unanticipated changes in the environment in which the assets operate can result in unexpected corrosion damage. Moreover, the combined effects of corrosion and mechanical damage, together with environmentally assisted material damage can result in unexpected failures. Given the typical lengths of subsea pipelines, most operators would consider an internal inspection method to use as the basis for the life extension study. These are conducted utilising intelligent inline inspection (ILI) tools that provide comprehensive coverage over the full length of the pipeline. In some cases, it is not possible to carry out an ILI inspection due to reduced product flows and the absence of launch and receive facilities etc. In these cases, tethered or bi-directional tools may be required. These options, however,
Figure 1. A high-resolution ultrasonic corrosion map of a subsea pipeline subject to degradation by microbial induced corrosion (MIC). The corrosion morphology can be compared directly with the predictions of the corrosion risk assessment.
Figure 2. Polar plots and cumulative thickness distributions generated.
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require the pipeline to be taken out of service for the duration of the inspection with associated production losses.
Pipeline targeted inspections online In this situation, an operator will need to consider an alternate means of inspection of the pipeline. Most operators would consider the use of a sampling or targeted inspection of selected locations along the length of the pipeline following a detailed corrosion risk assessment (CRA). The locations are selected on the basis of highest susceptibility to degradation as determined by the CRA. Not all circumstances are predictable, but many are. Examples include low points in the pipeline where water may collect, cooler locations where condensation may occur, or locations where inhibiters may have been ineffective and are no longer protecting the internal surfaces of the pipeline etc. However, when conducting an external sampling or targeted inspection, any access restrictions at the selected locations need to be assessed. Consideration should be given to whether the pipeline is buried, as well as the external coating type, as this can prove challenging to inspect through with certain inspection technologies. Removal of the coating could be carefully considered, however this will impact the life extension study, as removal of insulation/coating will affect the pipeline protection and condition. Sonomatic has developed an exciting new inspection technology that enables inspection to be conducted through certain challenging subsea coatings where conventional ultrasonic is ineffective. Dynamic response spectroscopy (DRS) is an innovative ultrasonic inspection technique for corrosion mapping through attenuative coatings. A custom DRS probe excites the steel with a range of low ultrasonic frequencies, which pass easily through the challenging coatings (such as neoprene, polypropylene/ polyethylene, composite wrap repairs, and Thermotite). The steel responds, vibrating at natural frequencies related to its thickness profile. Using advanced algorithms, these frequencies are extracted from the returning signal at each location and used to determine the steel thickness. Due to the reduced coverage achievable by conducting externally applied technologies, typically at a tiny fraction of the total line, the purpose of inspection is not to locate all the degradation present in each pipeline, or even to confidently locate the worst-case location. The actual
