Published on 3 August 2022
The International Marine Contractors Association’s (IMCA’s) latest guidance ‘Guidelines for the Measurement of Depth of Burial’ (IMCA S 029) aimed at both the offshore renewables and offshore oil and gas industries, looks at the different methods of measuring the depth of burial of subsea cables and pipelines together with factors influencing the depth of burial.
It also includes measuring the thickness of an embankment of crushed rock on top of a pipeline or cable; and provides guidance on measurement of depth of lowering – including explanation of the difference between lowering and burial or cover.
Subsea pipelines and cables are commonly buried in the seabed or covered with crushed rock to give them protection from anchoring and bottom trawling.
They can also be buried/covered to maintain an operating temperature and, in the case of pipelines, to be restrained from upheaval buckling. Some pipelines and cables are left exposed on the seabed to permit thermal expansion or left in an open trench designed to protect the line from passage of an anchor or trawl. ‘Depth of Burial’ or ‘Depth of Cover’ becomes a contractual requirement and therefore needs to be measured with equipment and procedures that produce results of known accuracy. IMCA S 029 gives clarity to this important topic.
As Stephen Peet, IMCA’s Technical Director, explained:
“Like all IMCA guidance this new document has been produced by a specially convened working group from members of the Offshore Survey Division – all experts in the field. They have created this 67-page document which looks at the different methods of measuring the depth of burial of subsea cables and pipelines together with factors influencing the depth of burial and is relevant for both offshore renewables and offshore oil and gas.”
The document includes sections on the methods for defining depth of burial or cover; selection of survey sensors; tone injection for active cable trackers; accuracy of DOB measurements; depth of burial measurement in different types of survey; reporting depth of burial; possible disputes in depth of burial measurement; developments in pipe and cable tracking as well as a useful introduction providing both an overview of methods of burying pipelines or cables and of equipment for measuring burial; clarification of terminology, a glossary; references and further ready and appendices focussing on Teledyne TSS 440 and PanGeo Sub-Bottom imager.