A strategy for assessment of non-stationary free spans

The objective of the present paper is to introduce and discuss a strategy for handling of pipeline free span with pronounced span development. The criticality in terms of fatigue and ultimate limit states of stationary free spans can be assessed using modern accepted guidelines and evaluation tools. For non-stationary spans however the situation is more complex and implies consideration of the actual temporal span condition (i.e. quasi-stationary or non-stationary spans) and span development (including self-burial). This means that optimal acceptance (and decision) criteria are location specific and require refined analysis tools linked to adopted inspection strategy and effect of potential span intervention. The paper discusses acceptance criteria and options for handling of: ○ long term criticality in terms of accumulated fatigue damage ○ short term criticality in terms of extreme bending during a storm condition (i.e. 100-year return period value) Focus will be on a probabilistic assessment of the span development process and link to the environmental condition, i.e. the link between span length, pipe/sea bed gap and sea-state. The methodology will be demonstrated via realistic examples.