Exploration • Drilling • Field Services
will be required by re-socketing or will even require replacement (Fig. 3). For low twist levels in a polyester rope with parallel sub-ropes, a small increase in fibre rope strength is observed. Tis is caused by higher friction interaction between the sub ropes leading to higher load shearing. For rope diameters 160mm and smaller, the breaking strength is not influenced by twist levels up to 0.5 turns per meter. However, a higher level of twist may eventually impact fibre rope break strength and durability.
Fig. 3. Damaged steel rope as a result of twisting.
Te objective is therefore to design torque-matched synthetic rope that ensures a longer steel cable lifetime.
Te ISO - Torque Matched - standard
requirement is for rotation at the connection point between steel wire and polyester rope to be less than 5° per steel cable lay length.
Te first premise to take into account is that if the steel cable to be deployed is right hand lay, then a torque-matched polyester rope must also be constructed as right hand lay. Similarly, if a steel chain is to be deployed in combination with steel cable and polyester rope, the same rule applies. In order to produce a torque-matched rope, and accurately predict rope torque response, the manufacturer should build a rope model which is validated by actual rope torque testing. Deep sea mooring rope manufacturer Bexco has developed and validated such a model deploying a state-of-the art test bench (Fig. 4.), which is capable of torque-match testing it’s made-to-measure DeepRope to ensure it has the same twist behaviour in operating conditions as its steel equivalent. To achieve torque-matching over a wide tension range, it is necessary to build a rope from multiple parallel sub-ropes. By way of example, a steel wire load of 100T may be complemented by a polyester (PET) equivalent of parallel deep sea rope consisting of three 33T sub-ropes, correctly sized in terms of composition and diameter. In this example, torque-matching needs to work consistently following bedding in and should meet the ISO ‘Torque Matched’ requirement from 0 to 55 per cent MBL at a minimum. To ensure a correctly configured, made-to-
measure deep sea mooring solution using fibre rope and steel wire which is also torque-matched, both manufacturer and EPC needs to consider the entire configuration.
Te combination of both polyester and steel rope
will provide a durable deepwater mooring solution provided that the torque-matching is ensured over a wide range to handle day -to-day operation as well as in storm conditions. Te increased focus on the interaction between
steel wire and polyester ropes has also come to the attention of certification companies, who have now included in their latest regulations that torque-match testing is mandatory when synthetic ropes are used in combination with steel wire. Tis means that certified torque-matched ropes will become more commonplace. Tis will be a positive development, given the greater longevity of use that will come as a result of the initial torque-matched installations and the subsequent growth potential of this particular segment of the market. ●
For more information ✔ at
www.engineerlive.com/iog Fig. 4. The Bexco test bench.
Karel Devos is R+D Manager with Bexco NV, Hamme, Belgium.
www.bexco.be
www.engineerlive.com 31
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84