Limit State Design Methodology for Offshore Pipelines against Ice Gouging - Industry Guidelines from the ICEPIPE JIP

Abstract

Ice loads on buried pipelines through ice-soil-pipeline interaction is a field with limited industry experience. As exploration in Arctic and cold climate regions increases it is of great importance to understand and to design for the challenges offshore pipelines must be able to withstand in these harsh areas with a suitable level of confidence. Together with thirteen industry partners, DNV has carried out a joint industry project in order to better define and therefore understand the Arctic specific challenges to pipelines. This project has developed initial industry guidelines for offshore pipelines in cold climate regions, in general and for ice scour in particular. A major design issue for Arctic offshore pipelines in shallow water is ice keels gouging the seabed and imposing loads on the pipeline through ice-soil-pipeline interaction. The industry has somewhat limited experience with deep ice gouges and ice keels interacting with buried pipelines. A common practice has been to bury the pipeline well below the deepest registered gouge mark in the relevant geographical area with the objective to limit the pipeline response. In order to render future projects in regions with severe ice gouges economically feasible whilst still being sufficiently safe there is a need to utilise modern design principles based upon statistical methods, advanced FE models calibrated to ice gouging tests, limit state design principles and strain based design. The ICE PIPE JIP provided the introduction of a more systematic approach for the identification, quantification and ranking of design uncertainties, and how this could be adopted to existing pipeline design methodologies and criteria. This paper presents some pertinent results and recommendations from the ICEPIPE JIP. The paper presents a sample case study for how the assessment of some elements of statistical uncertainty can be used in the definition of the 100 year return period ice gouge depth. This paper highlights one methodology for approaching this and it is emphasised that not all the steps that would be required in design are included in this brief paper. A discussion on the use of advanced FE tools in the ICE PIPE JIP is also presented.

Protecting Offshore Pipelines Against Drifting Ice: A Discussion on Standards and Guidelines

“…This research notwithstanding, there have been calls for additional testing [20,32]. As for numerical modelling, it has been used extensively by different research groups to simulate gouging processes [33], but model validation is 'non-trivial' [20] and it cannot yet capture all aspects of the interaction.…”

“…One such JIP (referred to as ICE PIPE), intended to supplement DNV OS F101, was dedicated to cold climate applications: ice gouging, permafrost instability, strudel scour, shore approaches. Some of the key findings of this JIP, addressing threats of gouging ice features to the main pipeline sections, are provided in Davies, et al [20]. The ICE PIPE guideline "takes the user through the stages of environmental data collection and analysis, determination of characteristic values for ice gouge parameters, and assessment of the pipeline load effect" [20].…”

“…Davies, et al [20] focus on uncertainties in measurement and interpretation of the bathymetry data, and what this entails for the validation of numerical models.…”

“…Some of the key findings of this JIP, addressing threats of gouging ice features to the main pipeline sections, are provided in Davies, et al [20]. The ICE PIPE guideline "takes the user through the stages of environmental data collection and analysis, determination of characteristic values for ice gouge parameters, and assessment of the pipeline load effect" [20]. The proposed calculation methodology was divided into three steps: 1.…”