Development and Testing of a Non-interlocked Hoop Strength Layer for Unbonded Flexible Pipe

摘要

Conventional flexible pipe for high pressure applications generally employs a high lay angle, interlocked steel hoop strength layer to prevent blow through of the internal pressure sheath through gaps between adjacent wraps. The interlocked hoop strength layer is referred to as "pressure armour" in ISO 13628-2/API 17J [1]. The interlocking is designed to prevent large gaps from opening between adjacent wraps. The internal pressure sheath must span the gap under the internal pressure loading, and meet the ISO 13628-2/API 17J requirement of no greater than 30% thickness reduction at the gap location with the interlocking wraps in the fully extended position. To simplify the design of the hoop strength layer so that composite materials can be employed, a means of controlling the gap and preventing internal pressure sheath blow through between noninterlocked rectangular cross section hoop strength layer helical wraps has been developed. The non-interlocked design comprises an anti-extrusion and gap control layer applied between the internal pressure sheath and hoop strength layer. This paper presents the design of this new layer, the requirements to qualify the layer, tests which were conducted to verify qualification, and a validated model based on the test results for use in design of unbonded flexible pipe employing noninterlocked composite hoop reinforcement. The advantages of a non-interlocked composite hoop strength layer in unbonded flexible pipe include lighter weight structures, reducing risk and cost for installation and operation, and corrosion resistance making it ideal for deepwater and ultra-deepwater applications.