OCEANOGRAPHIC ELECTRO-MECHANICAL CABLES pdf

CHAPTER 2 OCEANOGRAPHIC ELECTRO-MECHANICAL CABLES Albert G Berian (Reviewed and edited 2000 by Len Onderdonk) 1.0 CONSTRUCTION CHARACTERISTICS 2-5 1.1 Coincidence 2-5 1.2 Center Strength Member 2-5 1.3 Braided Outer Strength Member 2-5 1.4 Electro-Mechanical Wire Rope 2-5 1.5 Outer Single Served Strength Member 2-5 1.6 Outer Double Served Strength Member 2-5 1.7 3-4-5 Layer Served Strength Member 2-8 2.0 WORKING ENVIRONMENT 2-8 2.1 Flexing 2-8 2.2 Abrasion 2-9 2.3 Tension Cycling 2-9 2.4 Corrosion 2-9 2.5 Fish Bite 2-10 2.6 Abrasion Rate Factors 2-10 2.7 Kinking 2-10 2.8 Crushing 2-11 3.0 PARTS OF CONTRA-HELICALLYARMORED 2-11 EM CABLE 3.1 Direction of Lay 2-11 3.2 Lay Angle 2-12 3.3 Preform 2-12 3.4 Height of Helix 2-13 3.5 Percent Preform 2-13 3.6 Length of Lay 2-13 3.7 Pitch Diameter 2-14 3.8 Number of Armor Wires 2-14 3.9 Armor Coverage 2-16 3.10 Squeeze 2-16 3.11 Core 2-17 3.12 Water Blocked Core 2-18 2-2 4.0 PERFORMANCE CHARACTERSITICS OF 2-19 C-H-A, E-M CABLES 4.1 Torque Balance 2-19 4.2 Twist Balance 2-21 4.3 Crush Resistance 2-21 4.4 Corrosion Resistance 2-22 4.5 Abrasion Resistance 2-24 4.6 Elongation 2-24 4.7 Sea Water Buoyancy 2-24 4.8 Breaking Strength 2-24 5.0 MANUFACTURING PROCESSES FOR E-M 2-27 CABLES 5.1 Conductor Stranding 2-27 5.2 Insulation 2-27 5.3 Wet Test 2-28 5.4 Cabling 2-28 5.5 Braiding 2-28 5.6 Serving 2-28 5.7 Jacketing 2-29 5.8 Armoring 2-29 5.9 Prestressing 2-30 6.0 HANDLING E-M CABLES 2-33 6.1 Storage Before Use 2-33 6.2 Spooling Effect on E-M Cables 2-34 6.3 Smooth Drum Spooling 2-35 6.4 Tension Spooling Objectives 2-35 6.5 Tensions for Spooling 2-35 6.6 Lower Spooling Tensions 2-37 6.7 Grooved Drum Sleeves 2-37 6.8 Sheaves 2-37 7.0 FIELD INSPECTION AND TESTING 2-42 7.1 General 2-42 7.2 Required Inspections 2-42 7.3 Cable Record Book 2-42 7.4 Cable Log 2-43 2-3 7.5 Inspection 2-43 7.6 Visual Inspection Practices 2-43 7.7 Armor Tightness Inspection 2-44 7.8 Lay Length of the Outer Armor 2-46 7.9 Conductor Electrical Resistance 2-47 7.10 Outside Diameter 2-49 7.11 Need for Lubrication 2-51 7.12 Location of Open Conductor 2-53 7.13 Fault Location, Conductor Short 2-54 7.14 Re-Reeling 2-54 7.15 Cable Length Determination 2-54 8.0 RETIREMENT CRITERIA 2-55 8.1 Considerations 2-55 8.2 Broken Wire Criteria 2-56 8.3 Life Cycle Criteria 2-57 8.4 Non-Destructive Testing 2-58 9.0 CABLE MATERIALS 2-59 9.1 Conductors 2-59 9.2 Insulations 2-60 9.3 Shielding 2-61 9.4 Jackets 2-62 9.5 Armor 2-63 10.0 CONTRA-HELICALLY ARMORED E-M 2-65 CABLE SPECIFICATIONS 10.1 Performance vs. Construction Specification 2-65 10.2 Construction Specification 2-65 10.3 Performance Specification 2-66 11.0 AVAILABLE CABLE SERVICES 2-67 11.1 General 2-67 11.2 Spooling 2-69 11.3 Splicing 2-69 11.4 Fault Location 2-69 11.5 Reconditioning 2-69 11.6 Magnetic Marking 2-73 2-4 12.0 ACKNOWLEDGMENTS 2-74 13.0 BIBLIOGRAPHY 2-75 14.0 APPENDICIES 2-92 2-5 1.0 CONSTRUCTION CHARACTERISTICS Electro-mechanical (E-M) cables constitute a class of tension members which incorporate insulated electrical conductors. The spatial relationship of these two functional components may be: 1.1 Coincident (Figure 2-1), as in an insulated, copper-clad steel conductor conventionally used in sonobuoy and trailing cables of wire-guided missiles. 1.2 Center Strength Member (Figure 2-2), such as for elevator traveling control cables. In this, as in most constructions wherein the strength member and electrical component are separate elements, the strength member may be one of several metals or non-metallic materials. Also, the construction of the strength member may be a solid but more generally, it is a structure of metal or yarn filaments. The electrical components of the cable are arranged around the strength member and an outer covering jacket is usually used. 1.3 Braided Outer Strength Members (Figure 2-3), involve a center arrangement of electrical conductors (one, coax, twisted, pair, triad, etc.) with the braided metal or non-metal strength member external to the electrical conductors. Because of the mechanical frailty of the relatively fine filaments a protective covering or jacket is usually required. 1.4 Electro-Mechanical Wire Rope , (Figure 2-4), uses standard wire rope constructions; a three-strand is illustrated. The insulated electrical conductors can be located in two parts of the cross section, in the strand core and in the outer valleys or interstices. When conductors are placed in the outer interstices, a protective covering, or jacket is needed. 1.5 Outer Single Served Strength Member (Figure 2-5), utilizes metal or non-metal fibers which are helically wrapped around the electrical core which contains the insulated electrical conductors. The metal or non-metal fibers are helically wrapped around the electrical core so that they completely cover the surface. Because this construction has a high rotation vs tension characteristic, it is impractical as a tension member; the wrapping being used to increase resistance to mechanical damage. 1.6 Outer Double Served Member (Figure 2-6), has two helical serves of metal or non-metal fibers which are rapped around the electric cord. The two 2-6 2-7 2-8 helical wraps are usually served in opposite directions to obtain a low torque or low rotation vs. tension performance characteristic. An outer covering may be used; its purpose being primarily corrosion protection. 1.7 3, 4, 5 Layer Served Strength Member (Figure 2-7), utilize more layers of the served strength member to increase the ultimate tensile strength, or breaking strength of the E-M cable. The direction of helical serve for a three- layer serve is, from inner to outer serve, right-right-left (or Left-left-right). For a four-layer serve the directions are left-right-right-left, or a combination that permits proper load sharing and package stability. 2.0 WORKING ENVIRONMENT In the above discussion of construction of E-M cables, no mention was made of the working environment, which for this discussion is oceanographic. The hazards of this environment, which are important to E-M cables, include: 2.1 Flexing In most applications operating from ships there is constant motion in service with resulting bending of the E-M cable at points of changing direction, such as on sheaves, fairleads, winch drums, capstans, level winds, motion compensators, etc. 2-9 2.2 Abrasion This motion results in the development of two forms of abrasion; between cable internal components and external between the cable and the handling equipment. This abrasion degradation can progress to a point where either a failure occurs or it is observed to be unfit for continued use and is retired from service. The latter is, of course, the more desirable approach. The rate of abrasive wear varies with several operational factors including line speed, tension, cable to sheave alignment and bend diameter as a ratio of cable diameter. Also, maintenance factors such as allowing abrasive materials (sand, corrosion, etc.) to remain in the cable and maintaining the proper lubrication of rubbing metal parts have a significant affect on the deleterious effects of flexing. 2.3 Tension Cycling When deployed from a moving platform, the tension in the EM cable will vary constantly. The magnitude of the tension variations can be reduced by use of such devices as motion compensators. Because the E-M cable is an elastic member, it has a tension/elongation characteristic defined by its elastic modulus (see Appendix 1). As the magnitude of stretch varies, the components change their geometrical relationship and create internal friction very much similar to that in flexing. The same damage alleviating and enhancing factors apply as for flexing conditions. 2.4 Corrosion Applying to metal, primarily steel, this is a major concern in the marine environment. Galvanized steel is, because of its low life cycle cost, the most common metal used for the very common double layer armored cables. The galvanized coating, usually about 0.5 oz./ft 2 , is usually electrolytically dissolved very quickly leaving basic steel to be attacked by the sea water. Figure 2-8 shows the equivalent thickness to be about 0.0005 inch. Using an average surface reduction by corrosion for steel of 0.001 inch per year, this thickness would be completely eliminated in six months. 2-10 Figure 2-8 Thickness of Zn Coating on GIPS Armour Wires Usual specification 2 ft 0z 0.5 = = (inch) thicknesst = ρ ρρ ρ 3 ft lb density = ft lb 0.3125 1b oz 16 ft oz 0.5 12 t 2 2 == 3 1 ft lb 62.4 x 12 Znfor 0.03125 x 12 t == ρ in 0.0005 62.4 x 12 0.03125 x 12 t == 2.5 Fishbite This hazard applies to cables having an outer surface which is soft relative to steel. This class of cables include those with extruded outer coverings, or jackets, and those having a covering of braided yarns such as polyester and aramid. 2.6 Abrasion Rate Factor The rate of this degradation in internal surfaces such as interarmor surfaces can be reduced by maintaining a clean, lubricated condition. On outer cable surfaces accelerated wear is usually the result of improperly selected or installed handling equipment. . . 2.7 Kinking/Hockling A kink results when the coil of a cable is pulled to an increasingly smaller coil diameter to the point where permanent deformation of the cable occurs. E-M cables armored with multi-layers of round metal wires are most susceptible to [...]... tension The high concentration of compression force can cause permanent deformation of metal strength members and other components 3.0 PARTS OF CONTRA-HELICALLY ARMORED E-M CABLES Because over 90% of all E-M cables used in dynamic oceanographic systems use a contra-helical armor strength member, they will be discussed most completely in this chapter As shown in Figure 2-9, this type of E-M cable consists... equation is illustrated in Figure 2-18 The data in the chart was taken from a selection Of cables currently used in oceanographic applications The expected trend toward a unity value of armor ratio as the armor wire factor increases occurs because the: 2 d0 2 dI ratio becomes unity, or in extreme torque balanced cables may become less than unity The D0 DI ratio becomes very small as the diameter of armor... yield a relationship between cable breaking strength and cable O.D This relationship is shown in Appendix 20 2-27 5.0 MANUFACTURING PROCESSES FOR E-M CABLES The processes used to manufacture E-M cables differ from those used for general industrial cables in that much greater care in quality control is mandatory This greater attention to ensure the design integrity of components, subassemblies and... Stranding To decrease fiber bending stresses, the electrical conductors of E-M cables are stranded; i.e they contain several individual wires, common strandings being 7-19, and 37 The lay-up is usually “bunched” which means that all wires are twisted in the same direction Properties of copper conductors commonly used in oceanographic cables are shown in Appendix 3 5.2 Insulation The majority of electrical... indentation will continue until a contact surface is formed which results in a stable contact stress value 6.0 HANDLING E-M CABLES The discussion of handling E-M Cables starts with the assumptions that the cable had been properly specified and procured 6.1 Storage Before Use E-M cables are usually supplied on heavy duty steel or wood shipping reels The cable will be uniformly thread-layed on the reel;... decreasing sheave groove induced abrasion is the coating of the groove surfaces with a material such as polyurethane or Nylon 12 4.6 Elongation The percent elongation at 50% of UTS for sizes of cables which are typical to oceanographic use is listed in Appendix 17 This characteristic applies after length stabilization as described under “Prestressing” in the Manufacturing Process Section and for the same diameter... = armor wire diameter D = pitch diameter of armor layer θ = lay angle subscripts 0 = outer armor I = inner armor The derivation of this equation is shown in Appendix 2 The torque ratio of most oceanographic cables is between 1.5 and 2.0 With a trade-off for other performance factors, the torque ratio can be reduced to one Today, with the availability of proven software packages the design engineer... a plain cylindrical winch drum and is most commonly used on small oceanographic winches containing 1,000 to 2,000 meters of cable Because of the low deployment forces involved, the spooling onto these winches is less critical However, good practice dictates that a uniform thread-lay be used 6.4 Tension Spooling Objectives When longer cables are to be handled by a tension winch formalized spooling procedures... succeeding layers according to schedules which vary according to the experience of many able technicians The schedules shown in Table 1 apply for a selection of small diameter cables The tensions shown in Table 1 are typical for EM cables similar to those used in oil well work They will vary for different types of armor The schedule shown in Figure 2-22 displaying spooling tensions expressed as a percentage... This space permits greater relative movement of the individual armor wires as the cable is flexed Also, this space permits settling of the armor layers to a smaller diameter, a natural transition for E-M cables, without overcrowding the armor wires In a greatly overcrowded condition there will be insufficient space for all armor wires and one or more will be forced out to a large pitch diameter In this . CHAPTER 2 OCEANOGRAPHIC ELECTRO-MECHANICAL CABLES Albert G Berian (Reviewed and edited 2000 by Len Onderdonk) 1.0 . construction of E-M cables, no mention was made of the working environment, which for this discussion is oceanographic. The hazards of this environment, which are important to E-M cables, include:. other components. 3.0 PARTS OF CONTRA-HELICALLY ARMORED E-M CABLES Because over 90% of all E-M cables used in dynamic oceanographic systems use a contra-helical armor strength member,