Section 2 General guidelines on inspection of mooring system components

2.1.1 The anchor head, flukes and shank are to be examined for damage, including cracks or bending. The anchor shackle pin should be examined and renewed if excessively worn or bent. Moveable flukes should be free to rotate.

2.1.2 Bent flakes or shank should be heated and jacked in place according to an approved procedure, followed by Magnetic Particle Inspection.

2.2.1 Although swivels are no longer in common use, anchors have been lost due to corrosion of the threads engaging the swivel nut. Swivel nut threads should be carefully examined and if significant corrosion is found, the swivel should be removed or replaced.

Other types of chain will require special consideration.

2.3.2 The service environment of offshore mooring chain is more severe than the service environment for conventional ship anchoring chain. Offshore chain is exposed to service loads for a much longer period of time. The long-term exposure to cyclic loadings in sea-water magnifies the detrimental effect of geometric and metallurgical imperfections on fatigue life. Moreover, the increased number of links in offshore chains renders the chain more susceptible to failure from a statistical standpoint.

2.3.3 Due to the effect of notches, e.g., the stud footprint, higher strength steels such as that used for IACS R4 chain have a lower ratio of fatigue strength to static tensile strength than typical lower strength steel such as used for IACS R3 chain.

2.3.4 Since chain link diameter loss can be due to abrasion and corrosion, diameter measurements should be taken in the curved or bend region of the link and any area with excessive wear or gouging. Two diameter measurements should be taken 90 degrees apart. Particular attention should be given to the shoulder areas which normally contact the windlass or fairlead pockets.

Links should be rejected if the minimum crosssectional area is less than the minimum Rule chain size plus a margin for corrosion and wear between surveys, see Pt 3, Ch 10, 8.2 Corrosion and wear. If repair is permitted it should be done by qualified personnel using an approved procedure.

NOTE

WELD REPAIR IS NOT PERMITTED ON IACS R4 CHAIN (see B2.3.6).

Two diameter measurements should be taken 90 degrees apart.

2.3.5 Since studs prevent knots or twist problems during chain handling and support the sides of the links under load to reduce stretching and bending stresses, missing studs are not acceptable. Links with missing studs should be removed or the studs should be refitted using an approved procedure.

2.3.6 Where chain studs are secured by fillet welds on one end, the stud is likely to fall out if a stud is loose or the weld is cracked. Any axial or lateral movement is unacceptable and the link must be repaired or replaced.

Links with studs fillet welded on the flash-butt weld end of the stud are unacceptable.

Rejection of links with gaps exceeding 3 mm between the stud and the link at the flash-butt weld end of the stud should be considered. Closing the gap by renewing the fillet weld may be considered but see the note in B2.3.8.

2.3.7 Field repair of cracked welds should be avoided if at all possible. Welding must be performed by qualified personnel using approved procedures:

NOTE

WELD REPAIR IS NOT PERMITTED IN IACS R4 CHAIN.

Chains with studs mechanically locked in place on both ends may only be repaired by an approved mechanical squeezing procedure to reseat the stud.

2.3.8 Fillet welding of studs in both ends is not acceptable; nor is welding on the stud end adjacent to the link’s flash-butt weld.

Existing studs with fillet welds on both ends will require special consideration and will be subject to special crack detection methods. A reduction in mechanical properties in way of the flash-butt weld will normally be required.

2.3.9 Where chain studs are secured by press-fitting and mechanical locking, it is very difficult to quantify excessive looseness of chain studs. The decision to reject or accept a link with a loose stud must depend on the Surveyor's judgement of the overall condition of the chain complement.

Axial movement of studs of 1 mm or less is acceptable. Links with axial movement greater than 2 mm must be replaced by squeezing or removed. Acceptance of chain links with axial movements from 1 to 2 mm must be evaluated based on the environmental conditions of the unit's location and expected period of time before the chain is again available for inspection.

Lateral movement of studs up to 4 mm is acceptable.

2.3.10 Where links are damaged and have cracks, gouges and other surface defects (excluding weld cracks), they may be removed by grinding, provided B2.3.4 is complied with.

Links with surface defects which cannot be removed by grinding should be replaced.

2.4.1 Fairlead inspections should verify that all fairleads move freely about their respective pivot axes, to the full range of motion required for their proper operation. All bolts, nuts and other hardware used to secure the fairlead shafts should be inspected and replaced as required.

Fairlead attachment to the hull should be verified and NDT conducted as necessary.

NOTE

There have been cases of closing plates on the fairlead shaft coming loose due to corrosion of the threads of the securing bolts, resulting in serious damage to the fairlead arrangements and the complete jamming of the fairlead and chain. Consequently, the securing bolts should also be checked to ensure that the bolt material does not corrode preferentially should the sacrificial anode system fail to function in way of the fairlead.

2.4.2 Special attention should be given to the holding ability of the windlasses. The chain stopper and the resultant load path to the unit's structure should be inspected and its soundness verified.

2.4.3 It is essential that a link resting in a chain pocket makes contact with the fairlead at only the four shoulder areas of the link to avoid critical bending stresses in the link. Satisfactory chain support is to be verified, and excessive wear in the pockets should be repaired as required to prevent future damage to the chain.

2.4.4 Chain pockets may be repaired by welding in accordance with the standard procedures supplied by the fairlead/windlass manufacturer. Normally, the hardness of the pockets should be slightly softer than the hardness of the chain link and procedures must be specific for the chain quality used.

2.5.1 Fairleads are to be inspected in accordance with B2.4.1.

2.5.2 Special attention should be given to the holding ability of the winch and the satisfactory operation of the pawls, ratchets and braking equipment. The soundness of the resultant load path to the unit's structure should be verified.

Proper laying down of the wire on the winch drum should be verified to the satisfaction of the Surveyor and drums and spooling gear adjustments made if required.

2.6.2 Experience has shown that large numbers of anchors and chains are lost in service due to connecting link failure. Fatigue problems have resulted from poorly designed machined faces and corners. Joining shackles of Kenter or similar designs manufactured before 1984 are of particular concern. Joining shackles used for higher strength chains, such as ORQ and above, which do not have certificates of equivalent quality should be rejected.

Fatigue is considered to be the critical criterion in way of the machined surfaces. On the remaining surface, the profile should be ground smooth and MPI should be carried out upon completion of grinding. In general, the radius of the completed grinding operation should produce a recess with a minimum radius of 20 mm and a length along the link bar greater or equal to six times its depth.

NOTE

Sandblasting prior to MPI may change the machined surfaces and should be avoided. Alternative methods of cleaning should be used.

Where links are damaged and have cracks, gouges or other surface defects (excluding weld cracks), they may be removed by grinding, provided Pt 3, Ch 20, 2.3 Chain inspection criteria is complied with.

Links with surface defects which cannot be removed by grinding should be replaced.

2.6.4 Tapered pins holding the covers of connecting links together should make good contact at both ends and the recess of counterbore at the large end of the pin holder should be solidly plugged with a peened lead slug to prevent the pin from working out.

2.6.5 Any joining shackles of Kenter or similar designs which are loose upon reassembly should be rejected.

2.7.1 Acceptance criteria should be guided by ISO-Standard 4309-1981(E). Further insight may be gained from the discard guidance provided by API RP 2I, Figures 18 and 19.

2.7.2  It should be borne in mind that ISO-Standard 4309-1981(E) is primarily intended for lifting appliances where the Factor of Safety may be higher than for mooring wires.

2.7.3 The Surveyor should exercise great care in his interpretation of the condition of the wire. An obvious acceptance or rejection is comparatively easy, but the grey area between is difficult to evaluate. The Surveyor must make a sound evaluation and technical judgement based on all available evidence.

2.7.4 In general, the age or time in service of the wire does not directly have a bearing on the acceptance or rejection of the wire other than as a factor to be taken into consideration by the Surveyor when deciding on the extent of the survey.

2.7.5 100 per cent visual examination of wire ropes is to be carried out and diameter measurements should be performed.

2.7.7 Diameter measurements should be taken at approximately 110 metre intervals, at the discretion of the attending Surveyor. If areas of special interest are found, the survey may be concentrated on these areas and diameter measurements taken at much smaller intervals.

2.7.8 An internal examination should be undertaken as far as practicable if there are indications of severe internal corrosion or possible breakage of the core or wire breaks in underlying areas. See API RP 2I, Section 2.3.6.3, for guidance on the internal inspection of wire rope.

2.8.1 The cause of wire rope failures may be deduced from the observed damage to the rope. The information summarised in this sub-Section covers most types of wire rope failure. More detailed information, including photographic examples, is available in ISO-Standard 4309-1981(E) and API RP 2I.

2.8.3 Changes in rope diameter can be caused by external wear, interwire and interstrand wear, stretching or corrosion. A localised reduction in rope diameter may indicate a break in the core. Conversely, an increase in rope diameter may indicate a swollen core due to corrosion.

2.8.4 Wear on the crown of outer strands in the rope may be caused by rubbing against fairleads, unit structure or the sea bed, depending on the location of the wear. Internal wear between individual strands and wires in the rope is caused by friction and is accelerated by bending of the rope and corrosion.

2.8.6 Deformation, i.e., distortion of the rope from its normal construction, may result in an uneven stress distribution in the rope. Kinking, bending, scrubbing, crushing, and flattening are common wire rope deformations. Ropes with slight deformations will not lose significant strength. Severe distortions can accelerate deterioration and lead to premature failure.

2.8.7 Thermal damage, although rare for mooring ropes in normal service, may be indicated by discoloration. Prompt attention should be given to damage caused by excessively high or low temperatures. The effect of very low temperatures on wire rope is unclear except for the known detrimental effect on lubricants.