The first phase of the JIP is expected to run for six months and cost in the region of $250,000 and involve four regional oil and gas operators.
Due to an uneven seabed, tidal currents or scouring, some pipelines may develop free spans. A free span on a pipeline is where the seabed sediments have been eroded or scoured away and the pipeline is no longer supported on the seabed.
Pipeline free spans have been studied extensively over the last two decades. Though the extreme limit states of the pipeline are understood and defined in DNV guidelines, traditional analyses fall short during the pipeline’s operational phase on mobile seabeds, where free spans form, move and often disappear between pipeline surveys.
The aim of the JIP with Subsea Engineering Associates (SEA) is to demonstrate that the creation of an enhanced partial safety approach with the delivery of more accurate data may negate the need for often unnecessary and costly intervention. The project will then focus on developing a methodology to demonstrate a “˜do-nothing’ approach to mobile free spans that will meet the failure probability required by DNV-OS-F101.
ITF Regional Manager for Australia Peter Brazier said “Each year large sums of money are spent by regional pipeline operators on detailed Finite Element analysis of spans identified in the survey campaigns. These studies often recommend offshore intervention, more surveys and regular re-analysis. Due to the mobile nature of the seabed and the span lifecycle behaviour, in most cases no intervention or re-analysis is required.
“The methodology developed through the JIP will go beyond traditional approaches to span assessment. It will investigate significant variables to define more accurately the failure probability of subsea pipelines. This will give operators greater knowledge of the behaviour of the seabed and how this impacts on pipeline surveys and integrity,” said Mr Brazier.
“Accurately defining failure probability allows for more cost-effective and enhanced risk analysis decision making, which we believe will be of great interest to oil and gas operators. We are grateful for the support received. The project would have been impossible to do without ITF’s involvement,” said SEA Operations Manager Afton Galbraith.