Response of subsea pipelines to anchor impacts considering pipe–soil–rock interactions

Abstract

To safely operate subsea pipelines, protective measures must be taken against external forces such as dropped ship anchors. The responses to problems that occur while dropping anchors influence pipelines reinforced with rock berms and limit the prediction of pipe–soil interactions. In this study, laboratory experiments and finite element analysis (FEA) were used to analyze three interactions (pipe–soil–rock) simultaneously, under the scenario of anchor impact. Froude's scaling method was used in the experiments to examine the strain of the pipelines resulting from variations in the mechanical properties of the seabed, anchor weights (drop heights), burial depth of the pipeline in the seabed, and rock berm heights. Under the same conditions, FEA was performed using smooth particle hydrodynamics. Comparison of the pipeline strain results from experiments and FEA showed that the maximum error rate was 12%. The results indicated that the reduction in stress due to increases in rock berm height varied with two seabed properties. On average, this reduction was 20% effective, which is similar to an increase in the depth of seabed burial. Thus, additional protection measures using rock berms may substantially reduce the impact of dropped anchors on pipeline strain.