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Echo Yodel Freespan Assessment

Echo Yodel Freespan Assessment

Benefits
Atteris’ expertise in pipeline engineering provided the Client with assurance on the integrity of the Echo Yodel Pipeline from cessation of production to planned cleaning and flushing operations, without the need for costly subsea intervention.
Background
The Echo Yodel fields started operation in 2001 as a tie-back to Goodwyn A platform, 135km North-West of Karratha. Production ceased in 2012. A ROV survey of the pipeline in 2013 reported 102 anomalous span that exceeded the original maximum allowable span lengths.
Work Performed by Atteris

Atteris assessed the 102 anomalous freespans. A review of the ROV and MBES survey data was performed. The Level 1 and Level 2 freespan assessment was carried out in accordance with DNV RP F105.

The freespans were caused by scour along the pipeline and a review of the survey data revealed that the bottom roughness analyses were misleading.

Re-assessment of the screening (Level 1) span was conducted and revised allowable span lengths were determined, capturing updated metocean condition, new shut-in pressure of 1.5MPa and applying Finite Element Analyses to obtain a more accurate natural frequency.  The revised allowable span lengths were determined to be longer than the operating allowable span length. A freespan interaction check was also conducted.

A Level 2 freespan assessment was performed on the freespans that exceeded the revised allowable span criteria. This fatigue assessment indicated that there is sufficient remaining fatigue life up to the planned cleaning and flushing operations, when the pipeline will be made free of hydrocarbon.

Finally, Atteris also performed a check on the proposed pigging operation with a back pressure of 7MPa and determined that this pigging operation would not have an adverse effect on the fatigue life.

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