An aging offshore oil export pipeline had been operating to a pigging philosophy developed over a decade earlier. The strategy set a target of one pig run per month driven by concerns around water dropout and internal corrosion risk. In practice this frequency had never been achieved due to operational constraints at a third party operated unmanned receiving platform. Despite this the pipeline continued to demonstrate good integrity and minimal debris returns.
Jee was commissioned to review the existing pigging strategy and confirm an appropriate forward approach aligned with current operating conditions and integrity performance.
The original pigging frequency was based on historical assumptions that no longer reflected current operations. Production had declined, flow velocities had reduced and operating practices had changed particularly around water management and corrosion inhibition. Pig recovery constraints meant the defined pigging frequency was unachievable in practice.
The challenge was to determine whether the existing pigging regime was still required from an integrity perspective and to define a realistic strategy that maintained pipeline condition without unnecessary operational burden.
Jee carried out a comprehensive review of available data including historical pigging returns inspection results operating conditions and integrity assessments. The original drivers for pigging were reassessed against current evidence to confirm their continued relevance.
Pigging performance over more than ten years was analysed to understand debris generation and cleaning effectiveness. Inspection data from successive in line inspections and external ultrasonic inspection campaigns were reviewed to assess corrosion growth and remnant life. The operational pig design was also assessed including bypass configuration to understand stall risk at current flow rates.
The review demonstrated that water dropout was no longer a credible corrosion threat due to changes in operating practice and effective corrosion inhibitor management. Historical pigging data showed consistently low debris returns with no correlation between pigging frequency and internal corrosion performance.
Jee recommended a revised pigging strategy targeting a minimum of four pig runs per year with a target of six based on what operationally achievable and had been historically shown to maintain pipeline cleanliness and integrity. Guidance was provided on running pigs following abnormal events such as shutdowns or water injection along with pig design modifications in order to maintain pigging velocities within an acceptable range.
The revised pigging strategy aligned integrity requirements with operational reality reducing unnecessary operations while giving the operator confidence in long term pipeline performance.
For more information on Jee’s pigging capability, visit www.jee.co.uk/pigging.
To contact Jee’s Head of Pigging, Sean Tucker, email sean.tucker@jee.co.uk, or call +44 (0)1732 371 371.