Out of Box Approach to Ensure the Integrity of Aged Pipelines Protection Culverts
Authors: Molelputhenpura Kuriakose Mathew , Nath Nahum Kant , Adel Khalid , Awadhi Ibrahim Al 
Published: November 2016

Many GASCO pipelines cross major highways in Abu Dhabi through concrete culverts (lengths varying from 50 to 125m). Some culverts are in severely deteriorated condition and required immediate replacement. Collapse of culvert(s) may lead to failure of the pipeline resulting in Loss of Containment, environmental degradation and potential risks to personnel/neighbourhoods. This paper presents a techno-economical solution as an alternate to the repair/replacement option for safeguarding the integrity of the pipelines.

GASCO identified four severely deteriorated concrete culverts which are protecting 6nos vital oil/gas pipelines, for major repair/replacement. Performing the repair/replacement of these culverts pose challenges due to access restraints, traffic obstructions/diversions, massive civil works, risk of working in the live gas pipeline vicinity etc., with huge overall estimated cost and more than two years execution time. GASCO studied/explored different options including the repair/replacement of existing culverts and ended up with selecting the option of flooding the culverts with a self-compacting mixture of sand and water using specialized pumps which can satisfy/meet the technical, commercial aspects and extend the remnant life.

Detailed study was carried out to verify the various technical aspects and evaluate the methodology, with data collection of existing pipe sizes, pipeline wall thicknesses from pipe condition inspection reports, vehicle loads, vibration measurements due to vehicle movements at pipe depths and desktop evaluation of data. The existing pipelines wall thicknesses were checked for Barlow stress (Hoop stress), Circumferential Stress, Longitudinal Stress, Radial Stress and Fatigue check for Girth & Longitudinal Welds considering the overburden loads of earth/sand fill, vehicle cyclic load and internal pressure/temperature and found adequate. Methods of construction and different materials for filling were explored. In some culverts, there was not adequate headroom for people/ equipment access. The method of pumping sand (using special pumps) and compaction of each sand layer by water flooding was found to be the most suitable option in terms of technology, local equipment availability/easy mobilization, locally available filling material, reduced risk of working in the vicinity of live gas pipes, etc. The solution was successfully implemented for the four culverts (each 60m long) across the busy Abu Dhabi – Al Ain highway at Mussafah, in Sep-2015, within 2 months duration and resulted in a huge cost saving of AED 38millions.

The followed approach is a long term solution that can be executed by the in-house resources of maintenance team with some support from local contractors (for pumping facilities, etc.) and it also eliminates the future maintenance cost. This solution is first of its kind that was implemented among ADNOC group companies and can be shared with/ adopted by other companies having similar facilities to benefit from the cost optimization & other advantages.