The PHMSA Guidelines for Integrity Assessment of Cased Pipe state that long range ultrasonic testing using guided waves (GWUT or GWT) is the only 'Other Technology' which may be used to provide information about the condition of cased crossings where ILI cannot be applied. Otherwise, excavations and direct examinations are required unless a hydrotest is performed. However, to be acceptable to PHMSA there must be some assurance that the required 100% coverage can be attained. Enhancements to the guided wave test performance are therefore required such that full coverage can be assured in the majority of cases. The paper will describe advancements made in monitoring of cased and other inaccessible pipe by: i) Repeated monitoring using permanent sensors, allowing complex, but constant, responses from features in the crossing e.g. end seals, centering spacers, welds and other appurtenances, to be calibrated out and only changes in condition detected; ii) Enabling the rate of change of condition to be determined, thereby leading to prioritisation of remedial actions by the operator; iii) Providing quantitative assessment of flaw size, enabling engineering assessments to be made about pipeline condition, satisfying the legislative requirements of an Integrity Management Program.
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