When PoD Matters – Microbially Induced Corrosion (MIC)

Stuart Kenny

General Manager - Silverwing

The Non-Destructive Testing (NDT) industry has seen a step change in the last couple of decades. For many years NDT was primarily recognized for quality assurance during manufacturing, and therefore equipment and training requirements were focused on evaluating components during fabrication.

However, with aging plants and increased awareness of the consequences of in-service damage mechanisms, the NDT industry has shifted towards online inspection and integrity management.

Microbially Induced Corrosion (MIC) is a worldwide in-service integrity problem, commonly found in carbon steel pipelines and dead legs. It often manifests as isolated corrosion pits caused by biological growth. The main risk of MIC is its ability to eat through a pipe or tube in a matter of weeks, especially if equipment is left with stagnant, untreated water in it. It is often very isolated, narrow and is commonly referred to as the ‘needle in the haystack’.

Inspection and integrity engineers are often responsible for assessing the in-service risk of operating plants, and due to this significant responsibility, will often require assurance that the recommended NDT technology can reliably detect the potential integrity threats. If MIC is identified as a potential threat, a reliable NDT method is needed for rapid detection.

Probability of Detection (PoD) studies and demonstrations of minimum detectability are industry accepted processes that help provide this assurance and deliver the expected level of confidence for engineers making critical decisions. Engineers typically want to know what defects and how large they must be to be detected as well as how accurate sizing is.

Having recently launched the Pipescan HD™ Magnetic Flux Leakage (MFL) system, Eddyfi Technologies has completed an in-house assessment to determine the PoD for MIC and other isolated corrosion defects.

Detection Study

The first step was manufacturing representative defects in a series of function test plates. These were manufactured at the optimum thickness range for Pipescan HD and MFL. Below is a diagram detailing an example sample plate that was manufactured at 6, 8, 10 and 12mm wall thicknesses:

Each plate had 20 machined defects:

  • 1mmø @ 10, 20, 30, 40 and 50% wall loss
  • 2mmø @ 10, 20, 30, 40 and 50% wall loss
  • 3mmø @ 10, 20, 30, 40 and 50% wall loss
  • 5mmø @ 10, 20, 30, 40 and 50% wall loss
  • 10mmø @ 10, 20, 30, 40 and 50% wall loss

The below table represents the inspection capability of the new Pipescan HD system. This information clearly identifies the minimum detectability in relation to nominal wall thickness and coating. It should also be noted that all defects larger than those listed in the Min Detection column were detected above the required threshold level.

Defect type = flat bottomed vertical walled machined defect

Detection definition = indication visible on screen (possibility of background noise also present)

Conclusions

MFL technology has a proven track record for rapidly and reliably detecting corrosion, isolated pitting and other in-service damage that creates a reduction in material wall thickness. Historical MFL systems had worked on LED alarm electronics that may have had the ability for detection but didn’t provide a permanent record nor have the spatial resolution to differentiate adjacent defects. The new Pipescan HD has evolved the MFL output and has demonstrated with this study a ‘best in class’ performance for minimum detectability, Probability of Detection and resolution.

Increasing confidence of inspections, the Pipescan HD is the simple and effective solution for corrosion mapping. Contact one of our experts to learn more today.