Applus+ assesses Corrosion under Insulation (CUI) utilising RTD INCOTEST

23/09/2019

    There is a growing need to develop more versatile and cost-effective inspection solutions for insulated pipelines where removing insulation was previously considered the only way to determine wall thickness and remaining life. While the majority of high energy pipelines are insulated, most facilities, including hydrocarbon processing plants, power plants, terminals, pump stations, compressor stations, oil/gas gathering systems and offshore/subsea systems, require non-traditional solutions due to both design and operational constraints.

    A large power plant operator approached Applus+ to provide an inspection solution addressing its operational and system design challenges. The facility consisted of two combustion turbine generators (CTG), each 200 MW maximum and each followed by a heat recovery steam generator (HRSG) with insulated high energy piping (HEP). The two HRSGs were heated from the CTG exhaust gases to generate steam. The generated steam was channeled into a single steam turbine generator (STG) of 235 MW maximum.

    High energy piping (HEP) can be susceptible to increased fatigue, wear, and other forms of degradation due to repeated stop-start operation. Plant performance needs to be studied using existing instrumentation to understand the causes of gradual deterioration.

    Furthermore, the positive and negative aspects of plant management need to be understood. Baseline and routine inspections can assist in proper management to identify damage and monitor degradation. Removing and installing insulation on HEP is a timely and costly process, with miles of piping, different elevations, and various design configurations. Given the power plant’s impact on the workforce and community, preventing an incident or unplanned outage from occurring became the top priority for Applus+ RTD’s client, along with ensuring that system reliability was providing a competitive advantage by reducing the unknowns within the facility.

    Very early in the project, it was decided that a nonintrusive inspection technique was preferred. This decision was made due to the time-consuming and expensive process of removing and reapplying insulation, attempting to screen affected areas and ultimately assessing the pipe conditions using conventional external non-destructive evaluation methods to access challenging locations. RTD INCOTEST, a non-invasive ultra-high resolution pulsed eddy current inspection solution, was the chosen technology as it provides 100% overlapping inspection of the pipe and has the versatility to meet the timing associated with the limited access and design challenges of the system.

    The inspection was completed on the two HRGS units, providing a baseline assessment at around 180 designated corrosion monitoring locations (CMLs) on the feed water piping without removal of insulation, ranging in schedules, 80 through 160/XH, and diameters, 4NPS through 12NPS. The CMLs were established by the operator’s engineers, primarily focusing on areas susceptible to flow-accelerated corrosion/erosion, and stagnant areas such as bypasses and dead legs. No areas of immediate concern were noted, but a baseline representation was made to establish corrosion rates and future inspection intervals and remaining life estimations. Cost savings were derived from not having to remove and reinstall insulation to inspect piping using conventional methods. Leaving the insulation undisturbed provided significant cost savings as well as yielding shorter project timelines.