5.5.2 “Improvements in Winch Design Guide AM11” Study
Chapter 8: Conclusions and Recommendations
This paper tried to give a better understanding of the 2 design methods (LRFD and WSD) used for reel design. The 2 methods discussed and compared from their requirements point of view and their limitations were discussed in light of the latest studies regarding winch design and spooled product (i.e.
wire, rope, etc.) behavior when subjected to reeling tension (i.e. rope relaxation, friction between layers, etc.). FEA models were built based on the specific requirements of each of the 2 methods and the results obtained were commented upon.
All in all, there are a lot of grey areas and situations where further research on products with similar characteristics as umbilicals is needed in order to reduce the amount of unknowns and give a better understanding on how loads actually act within the product layers and what is their overall combined effect on the reel structure. Friction between product layers that would lead to a reduction in the actual spooling tension (maybe close to 0 in some layers) and the damping effect under spooling tension of products with reduced lateral rigidity on the drum and flange pressures are just 2 areas where further research and solid results could prove that lower values for these loads could be considered, thus lighter designs could be obtained.
Reels in general seem to be one of the least studied equipment in the Offshore and Oil and Gas industry. The assumption that they could be considered and designed as winches has its limitations, especially when it comes to determining the loads generated by product spooling. Both design and design review is difficult because there is no specific set of design rules or a recommended practice guide, so it comes down to each engineer’s way of interpreting the general design requirements of both LRFD and WSD methods. Although that, from discussions with reel designers, some engineers prefer the WSD method which, together with DNV no. 2.22 standard, provide a more “calibrated-to-winch/reel-design” set of rules, maybe others use LRFD which only provides general design rules and a lot of areas where assumptions have to be made. This might lead to the fact that, although all the assumptions are according to the standard requirements, the overall result could not be in accordance with the specifics of reels.
From the design exercise performed, the results and relative easier way of designing and identifying load cases and building load combinations, but also the fact that WSD is more calibrated to winch design, which is assumed similar to a certain point with reel design, WSD seems to be more suitable for reel design
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than LRFD. Probably, if a new standard based on LRFD, but focused on the specifics of reels were to be created, then the methods might be at least similar.
Finally, the delicate matter of testing is not covered by any of the standards and this is considered to be an important area that needs to be regulated.
The overall conclusion, not just by analyzing the current situation in terms of design standards available, but also from discussions with people from the industry, there is a need of a “Recommended Practice Guide” built on one of the 2 design methods that would summarize the general design rules to be used, how and what loads to be considered, to offer standard solvings for various details of the structure (i.e. what type drive connection will be more suitable for a certain dimension of reel, etc.), what load tests to be performed, etc., but calibrated on the particularities of reels and based on studies directly relevant to reels and the products they transport.
61 Bibliography
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9. DNV presentation on “Hoop Stress in Multi-layer Drums”,18th January 2011
10. Song, K.K., ODECO Engineers Inc.; Rao, G.P., Childers, Mark A., “Large Wire Mooring Winch Drum Analysis and Design Criteria” 8548-PA, April 1980
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accessed august 2012
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