Marine cable fault is analysed easy sailors were injured

by:SanTong     2021-02-04
Sailors at sea will not only face many dangerous, even after the ship docked in the harbor, still need to safety procedures and equipment to protect the safety of the crew and dock workers. The dock for the ship's mooring rope can be important. With the lifeboat and need only in case of an emergency such as fire extinguishers, use different types of items each time ships will use Marine cable, so it needs regular or daily maintenance. Yet even regular maintenance Marine cable, may still occur accident. But the important thing is we need to learn lessons from the accident, so as not to happen again. In LNG carrier 'Zarga' accident, Marine cable rupture suddenly, a standing in the security area specified personnel was hit by a rope and seriously injured.   When such accident, not only need to have a formal investigation to determine the reason. More important is to survey can also provide some Suggestions and measures should be taken, in order to ensure that similar serious accident won't happen again. By the shell international trading and shipping company ( STASCo) Operations, big Q - in the world Max type LNG ship Zarga, storage capacity of 266000 cubic meters. Because of its size, can only anchor milford natural gas terminal in the UK. When using the spring along the wharf repositioned the ship, one of the first spring fracture, the high modulus polyethylene ( HMPE) Made of the Marine cable in fracture near the guide roller, guide roller change the direction of the cable, so the cable can arrive with the mooring winch fairlead form an Angle of 90 degrees. PP/PET (within the cable tail Polypropylene/polyvinyl acetate) Energy lead to broken cable shrinkage at a high speed. Due to complicated springback trajectory, even in the specified safety area, cable still hit is monitoring operation staff. And the other part of the Marine cable ( Back to the warping machine) Landed on the deck and no obvious rebound.   What causes the cable broken? According to the bureau of maritime accident ( MAIB) Security bulletins, without any reason. The report pointed out that in the Marine cable, after the residual strength of lower cable overload and fracture. MAIB report further pointed out that reduce the strength of the rope is the result of comprehensive shaping of many factors, including: exposure in repeated load, repeated bending and radial compression for a long period of time, the impact load and lesbian fatigue, shock produced by other accessories deck bending load and lesbian fatigue, cyclic loading and high strength among the port. Fracture of the spring 44 mm in diameter, strength for optimization, structure is three-ply braid and a layer of protection, the core is Dyneema ® SK75, shielding by polyester ( PET) Made, inside and outside layers separated by insulating rubber self-adhesive tape. 22 meters long, 275 meters long cable is equipped with a diameter of 88 mm (PP/PET cable tail. According to reports, one of the problems with the Marine cable is the lay length of cable core long and twist is very low, and in the middle of the insulating rubber self-adhesive tape and outer PET protection is very tight. This type of structure, process under axial compression, the introduction of cable kink become more tight. Local accumulation of fiber that can lead to kink region, due to tight cover Marine cable can't expand, increase internal friction lead to local extreme wear. Therefore, the other complete strand is more likely to fracture because of overload.   The report concluded that although the cable is to use Dyneema ® SK75 fiber, but the design method of the Marine cable should not be used for the mooring Q - Max type LNG ship. Therefore, the cable supplier has this type of product from the Q - Max type ship removed from market. In order to ensure the mooring cable can fully satisfy all the requirements, the DSM advice in the type of hardware, the mooring operation ports and environmental conditions for detailed analysis. DSM can help customers to analyze such, in cable design, protective layer and the connection to provide advice. DSM also advised to creep calculation of the cable, to ensure the service life in a warm environment, such as the Middle East and other regions. Calculated according to the creep analysis, manufacturer can design a more suitable cable.
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