Pipeline Inspection

Pipeline inspection is part of pipeline integrity management for keeping the pipeline in good condition. The rules governing inspection are the pipeline safety regulation. In most cases, the pipeline is inspected regularly. 

The pipeline safety regulations require that the operator ensure that a pipeline is maintained in an efficient state, in efficient working order, and in good repair. In fact, the pipeline operator has a vested interest in the pipeline being operated effectively and safely to satisfy the appropriate authority and save the failure cost in environment, loss of production, and repair. The pipeline inspection includes external inspection and internal inspection. The subsea pipeline external inspection looks at the pipeline's external condition, such as concrete weight coating. trench and concrete mattress losses, marine growth, anode wastage, and corrosion, free span and global buckling condition, and damages due to external load through visual observation. The subsea pipeline internal inspection is normally carried out though nondestructive testing techniques and technologies by intelligent pigs, such as magnetic-flux leakage technology in axial and circumferential conditions, ultrasound technologies, eddy-current technologies, and other technologies. 

The table below summarize the common type of survey and inspection methods for subsea pipelines. 

The abbreviationsin the table are defined as

• RAT : Rope access technicians; rope access is a means of working at height or depths in location that would be difficult or dangerous to reach by other means
• GI : General imaging, inspection using side scan sonar
• GVI : General visual imaging, using cameras
• NDT : Nondestructive testing
• FMD : Flooded member detection
• CP : Cathodic protection
• ROTV : Remotely operated towed vehicle
• WROV : Work-class remotely operated vehicle

In DNV RP F116, there are some other inspection method that can used to maintain subsea pipeline

• CVI : Close visual inspection
  A high standard of cleaning is required for this type of inspection, all hard and soft marine growth should be removed. The purpose of the inspection is to establish a detailed inspection of an area of specific interest. Requires either a diver or workclass ROV.
• HPS : Hig hprecison survey
  A high accuracy positional survey to determine the absolute position and relative year to year lateral movement of the pipeline on the seabed. This is achieved using a workclass pipeline ROV (as used for GVI), in conjunction with high accuracy calibrated positional equipment (e.g. high performance corrected DGPS, transponders (USBL/ LBL systems), ROV mounted survey quality gyro and motion sensor, high frequency doppler velocity log etc.). Inspection rate can be expected to be slower and will require more calibration time than standard GVI.
• ILI : In-line inspection
  Intelligent pigging of the pipeline. Utilizing various non-destructive testing (NDT) methods to measure continuous end to end pipeline wall thickness loss or pipeline anomalies/defects.
• Monitoring
  Following up of corrosion probes, impressed current system, process parameters, fluid composition and any onshore monitoring of load/stresses.

Source :
Yong Bai, Qiang Bai (2014), Subsea Pipeline Integrity and Risk Management, Elsevier
Det Norske Veritas Recommended Practice (DNV RP F116) : Integrity Management of Submarine Pipeline System