Higher Order Modes Clusters - HOMC

During an inspection program carrying out corrosion inspection on trunnions supporting process pipe work, the Mistras inspection team encountered a trunnion which displayed evidence of severe corrosion on the process pipe work within the trunnion area. Due to the severity of this corrosion and the nature of the pipe work under inspection this discovery warranted immediate reporting to the platform Inspection engineer.

The inspection engineer questioned the accuracy of the discovery and needed to cross check the Mistras findings with another method. Further visual inspection was then conducted on the trunnion by using a video scope inserted into the trunnion via a small access hole, this allowed good access for the video probe to record the actual condition of the pipe work within the trunnion. The video scope inspection confirmed that the pipework was indeed suffering from serious corrosion at the location identified by the Mistras technicians.

The need for the inspection engineer to confirm the Mistras finding was born out due to the relative newness of the pipework and trunnion which was less than eighteen months old. The rate of corrosion at this location and the surprise to the inspection engineer will now require further investigation to uncover the reasons behind this premature rate of corrosion on this specific location.

The inspection of pipe work trunnions within the oil & gas, Petrochemical and similarly associated industries has for many years been extremely difficult to achieve due to geometric and access issues limiting the inspection method to the use of mainly radiography. With radiography requiring the use of ionising radiation, safe barrier distances and all associated safety implications and planning, an alternative method has been sought that negated the use of dangerous substances and does not limit any close by work scopes or personnel performing their duties.

Mistras solution to this inspection requirement is the use of proprietary technology allowing the efficient scanning of the trunnion area by using an ultrasonic based method that provides a guided wave scan covering the trunnion footprint. Depending on the size of the trunnion it’s possible to obtain a full trunnion scan in one scan. Larger trunnions will require scans from multiple sides to give full coverage but in average it’s possible to fully inspect a trunnion within 30 minutes depending on the size of the trunnion and severity of the corrosion.

Advantages of the Mistras method.

  • Fast screening – typically 30 minutes per trunnion / location
  • Minimal personnel – usually 1-2 technicians depending on scope of work.
  • Minimal equipment – typically one UT set sized unit with probes and leads.
  • A and C scan images on a typical colour pallet for easy defect identification, and categorisation.

Easily deployable by rope access.