Advances on the Analysis of Critical Failure Modes of Subsea Umbilicals - Excessive Crush Loading
- Mimi Batrony (Oceaneering) | Ross Doak (OII) | Anna Bordner (OII)
- Document ID
- Offshore Technology Conference
- Offshore Technology Conference, 30 April-3 May, Houston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Offshore Technology Conference
- 7.1.8 Asset Integrity, 4.2.4 Risers, 4.5.7 Controls and Umbilicals
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The amount of crush load that steel tube umbilicals can sustain frominstallation tensioners can significantly influence the cost of deployment,particularly in deepwater developments.
As installation vessel selection has to be made, in most cases, well beforephysical testing of umbilical samples, umbilical installation crush limits canbe assessed by engineering analytical methods. It is, therefore, important thatthese crush load limits are defined realistically and derived using verifiablyaccurate methods. This requires fundamental understanding of the failure modesof components inside an umbilical subject to crush loading and analysis toolswhich are calibrated against actual test data.
This paper presents a preliminary study comparing experimental results withUFlex simulations on a sample steel tube umbilical under crush loading.Conclusions are drawn on the influence of test sample length on experimentalresults, and the direction of future work is outlined.
Developing deepwater oil and gas fields brings fresh challenges, particularlywhen installing infrastructure such as subsea umbilicals and other flexiblelines. With the water depth at some well locations now surpassing 3000 m, theweight of suspended umbilical length that must be handled during installationoperations can be substantial.
The conventional means of gripping an umbilical during deployment is by way oftensioner systems that control payout and hold the suspended weight of theumbilical. Typically tensioners feature two or more opposed caterpillar tracks,each fitted with a row of v-shaped pads that come together to grip the outerjacket of the umbilical. The frictional force required to react against thetension resulting from the mass of suspended umbilical is directly proportionalto the level of crush force applied radially to the umbilical by these v-shapedpads. Therefore, it is of interest to both manufacturers and installers todetermine the maximum allowable crushing load that can be applied to anumbilical without damaging the internal components.
Published studies have focused primarily on modeling the umbilical crushloading using FEA methods. Dieumegard and Fellows (2003) describe the designand installation of a deepwater metallic tube umbilical and give reference tothe correlation of crush test results with FEA software. Dixon and Jackson(2003) also consider the FEA modeling of a flexible riser for deepwater use,modeling installation crush through use of the 3D non-linear finite elementsoftware tool, ABAQUS Explicit.
The aim of this work was to study the mechanism governing steel tube failureunder crush, initially through small scale testing of individual samples,followed by further testing within a cabled umbilical. These experimentalresults are then compared against linear and non-linear FEA models generatedusing UFlex.
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