Stabilization of Pipeline crossing support using lounge base grout bags

Fluids are transferred from one place to another in different ways, one of which is through a pipeline. One of the ways of transporting hydrocarbons to the coast is through pipelines laid on the seabed (or buried under the seabed). In addition to these main lines (transmission from wellhead to shore), oil and gas fields require a number of interfiled pipelines that connect satellite platforms to the main platform.Pipeline free spans occur where bottom roughness on the seabed creates a situation where the pipeline spans between high points. Such spanning beyond certain prescribed limits creates over stressing during hydro test or operations. Spans are corrected by placing grout bags underneath the pipeline and filling them with corresponding materials.Excessive unsupported spans have to be corrected prior to pipeline pre-commissioning (flooding) so it is often advantageous to combine free span correction and pipeline pre-commissioning contracts. Over a rough seabed or on a seabed subject to scour, free spans can occur when contact between a subsea pipeline and the seabed is lost over an acceptable distance. When this exceeds the allowable free span length, design stresses can be exceeded, and a vortex-induced vibration (VIV) response can be initiated, resulting in the risk of fatigue failure. If this is not predicted and controlled properly, it will affect pipeline integrity, leading to expensive rectification and intervention work. Free span analysis consisted primarily of a screening check in which the as-found free spans from Remotely Operated Vehicle (ROV) or multiband Side Scan Sonar (SSS) inspection survey were compared against the allowable design lengths and determine the expected fatigue life of a free span that may be experiencing Vortex Induced Vibration (VIV). Free spans are acceptable if the calculated fatigue life exceeds the design life criteria. This paper describes the free span analysis developed to perform detailed free span engineering assessments, incorporating the latest survey and as-laid conditions. This analysis follows a methodology in standard code DNVGL RP F۱۰۵ that has been accepted and used by operators to produce more accurate and less conservative free span analysis results, leading to a subsea pipeline integrity management strategy with fewer unnecessary interventions and greater cost benefits.