Guidelines for safe cable crossing over a pipeline

Abstract

© 2020 Elsevier Ltd

High voltage submarine cables are increasingly being installed in existing and new offshore oil and gas fields for power supply and control purposes. These power cables are both large and with a high submerged weight, which poses a challenge when designing a safe, maintenance free (economical), and fit-for-purpose crossing over a pipeline. Damage to subsea pipeline crossings caused by deterioration of a crossing support, field joint materials and cover components is well known in the industry, particularly with old pipelines. Crossing cables over an existing pipeline should be avoided whenever economical and practical. However, it is inevitable in some situations to use the existing pipeline (unburied) as the crossing support to a new cable/umbilical. In these situations, crossing the cable/umbilical over the existing pipeline may be a cost-effective and worthy consideration. However, there are no explicit guidelines or criteria in the industry concerning the acceptable practice of design and construction of crossings. The only clear recommendation is relating to pipeline separation distances. This paper documents a recent case study of damage of a field joint coating at a crossing of an existing pipeline by a 132 kV subsea cable of 191 mm outside diameter. Investigation of the damage on site revealed that it was caused by lateral movement of the cable under the influence of hydrodynamic forces. Further to investigation and assessment of the damage of the case study presented here, the paper proposes some guidelines for the safe design and construction of cable crossing. Another objective of this paper is to invite further evaluation of the proposed guidelines so that appropriate crossing design requirements can be further developed and standardised.