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Pipeline Inspection

Subsea systems should be monitored or inspected regularly, internally and externally.
The inspection can provide such information as: geometry variation (dent, wrinkle,
buckle, etc.), wall thickness variation (metal loss), corrosion, crack, leak, etc.
The advantages and disadvantages of internal and external inspections are as follows:

• Internal inspection: Applicable for inaccessible (buried or concrete/insulation coated) pipes. May have to shut-down the system to send pigs. Pigs may be stopped or lost due to pipe buckle or pressure loss due to large hole on the pipe.

• External inspection: Applicable for un-piggable line. No need to shut-down the system. Good for partial suspicious area inspection, such as manifold, jumper connection, riser, etc.

Self-crawling intelligent pigs have been developed to perform the In-line inspection (ILI)
without interrupting the production. The external inspections or integrity monitoring
systems are performed by ROV or tools mounted on the pipeline (Figure 23.1).
Magnetic and ultrasonic tools are commonly used to detect corrosion, crack, geometry
and wall thickness variations. Detecting a leak as early as possible will reduce the
environmental damage. The current leak detection systems available for subsea
pipelines are;

• Ultrasonic - transmit ultrasonic waves and receive/record reflected waves
• Acoustics - monitor/detect noise or pressure change being created by a rupture or sudden leak
• Dye detectors - detect optical fluorescent leak visually by a laser beam
• Fiber optics - detect leaks by hydrophones, accelerometers, temperature monitoring sensors installed on a distributed fiber optic cable along the pipeline
• Flow balance - detect leak by monitoring volumetric flow rate, pressure, and temperature

 

The effective integrity monitoring and management planning allows the operator to
reduce uncertainties and risks associated with riser fatigue, corrosion build-up, hydrate
plug or wax formation conditions, etc.
The subsea integrity monitoring service providers include:

• Genesis SIG (Subsea Integrity Group)
• Come Monday, Inc.
• IICORR (Integrity Inspection Corrosion)
• Fugro Structural Monitoring (FSM)
• 2H Offshore
• MCS
• DeepSea Monitoring Solutions (DMS), etc.

References
[1] Genesis SIG Website, www.genesis-sig.com
[2] TDW Williamson Company Brochure
[3] Offshore Pipelines, Guo, Boyun, et. al, Elsevier, 2005


Source: Lee, Jaeyoung. 2007. Introduction to Offshore Pipelines and Risers.