Section 3 Offshore Mooring chain cables

3.1.1 Provision is made in this Section for five grades, R3, R3S, R4, R4S and R5, of stud link chain and studless flash butt welded chain cable intended for offshore mooring applications such as mooring of mobile offshore units, mooring of floating production units, offshore loading systems and gravity based structures during fabrication. Special consideration will be given to the use of grades outside the existing scope.

3.1.2 Design of stud link chain cables must be to a recognised Standard, such as ISO 1704. For studless chain the shape and dimensions are to comply with the requirements of this Section. Non-Standard designs of chain are to be subject to special consideration, and may require a fatigue analysis and tests to confirm relevant performance.

3.1.3 In addition, chain cable conforming to the requirements of the current edition of API specification 2F is acceptable provided that it has been manufactured, inspected and tested under survey by LR, and that the bar stock has also been certified by LR in accordance with Ch 3, 9 Bars for welded chain cables.

3.1.4 The studless link chain is generally expected to be deployed only once, being intended for long-term mooring applications with a pre-determined service life.

3.2.1 All grades of chain cable and fittings are to be manufactured by approved procedures at works approved by LR. A list of approved manufacturers for offshore mooring chain cables is published separately by LR.

3.2.2 Approval is confined to a single works and is limited to one grade of cable made from bar from a nominated and approved supplier. Separate approvals are required if steel bar is supplied from more than one works and for other grades of cable, see also Ch 3, 9 Bars for welded chain cables.

3.2.3 Details of the method of manufacture and the specification of the steel, are to be submitted.

3.2.4 Offshore mooring chains are to be made in continuous lengths by flash-butt welding.

3.2.5 Bar material may be heated by electric resistance, induction or in a furnace. For electrical resistance heating or induction heating, the process is to be controlled by an optical heat sensor. For furnace heating, thermocouples in close proximity to the bars are to be used for control and the temperature is to be continuously recorded. In both cases, the controls are to be checked at least once every eight hours and records taken.

3.2.6 The following welding parameters (as approved in the weld procedure) are to be controlled during welding of each link:

1. platen motion;

2. current as a function of time; and

3. hydraulic pressure.

The controls are to be checked at least once every four hours and records taken.

3.2.7 The records of bar heating, flash-butt welding and heat treatment are to be made available to the Surveyor when required.

3.2.8 As far as practicable, consecutive links in all chain cable should originate from a single batch of bar stock (see Ch 3, 9.6 Mechanical tests 9.6.1) and indicating marks should be stamped on the final link formed from one batch and the first link formed from a separate batch.

3.3.1 The studs are to be made of steel corresponding to that of the chain or in compliance with a specification approved by LR. In general, the carbon content should not exceed 0,23 per cent if the studs are to be welded in place.

3.3.2 Studs may be welded into grade R3 and R3S chains. The welding of studs into grade R4, R4S and R5 chain is not permitted unless specially approved.

3.3.3 In all cases where studs are welded into links, this is to be carried out in accordance with Ch 10, 2.7 Welding of studs. The visual and NDE inspection of the stud welds is to be carried out in accordance with Ch 10, 3.6 Proof load tests and non-destructive examination.

3.3.4 The size of the stud welds is to be in accordance with Figure 10.3.1 Dimensions and tolerances of stud welds.

Figure 10.3.1 Dimensions and tolerances of stud welds

3.3.5 Where plastic straining is used to set studs, the applied load is not to be greater than that qualified in approval tests. The combined effect of shape and depth of the impression of the stud in the link is not to cause any harmful notch effect or stress concentration.

3.4.1 The chain is to be normalised, normalised and tempered or quenched and tempered in accordance with the specification approved by LR.

3.4.2 The chains are to be heat treated in a continuous furnace; batch heat treatment is not permitted unless specially approved.

3.4.3 The temperature and time, or temperature and chain speed, are to be controlled and continuously recorded.

3.4.4 Heat treatment is to be carried out prior to the proof loading, breaking tests and sample mechanical tests.

3.4.5 The heat treatment furnace is to be properly constructed, efficiently maintained and has adequate means of temperature control. Calibration of furnaces is to be verified by measurement and recording of a calibration test piece with dimensions equivalent to the maximum size of link manufactured.

3.5.1 All chain cables are to be subjected to proof load tests, non-destructive examination, sample break load tests and sample mechanical tests after final heat treatment in the presence of a Surveyor. In addition to the requirements stated in this Chapter, attention must be given to any relevant statutory requirements of the National Authority of the country in which the ship is to be registered.

3.5.2 The chain is to be shot or sand-blasted prior to testing in order to ensure that its surfaces are free from scale, paint or other coating for inspection and have a suitably prepared surface in accordance with the NDE standard applied.

3.5.3 All non-destructive examination is to be carried out in accordance with approved procedures, in accordance with Ch 1, 5 Non-destructive examination.

3.6.1 The entire length of chain cable is to be subjected to a proof loading test at a Proving Establishment recognised by LR. A list of recognised Proving Establishments is published in the Class Direct section of LR’s website, http://www.lr.org. The chain cable is to withstand the load given inCh 10, 3.6 Proof load tests and non-destructive examination 3.6.1 for the appropriate grade and size of cable.

3.6.2 Care should be taken to obtain a uniform stress distribution in the links being tested.

3.6.3 On completion of the proof load test, each link is to be visually examined and is to be free from significant defects such as mill defects, surface cracks, dents and cuts, especially where gripped by clamping dies during flash butt welding. Studs are to be securely fastened and any burrs, irregularities and rough edges are to be removed by careful grinding. In order to ensure adequate inspection, the chain is to be positioned to facilitate access to all surfaces.

3.6.4 All flash butt welds, including the area gripped by the clamping dies on every link, plus 10 per cent of links on all accessible surfaces, are to be examined by magnetic particle inspection in accordance with standards recognized by LR, using wet continuous fluorescent magnetization technique. Non-fluorescent techniques can be accepted in special cases where the standard inspection procedures are impractical. The inspected area is to be free from cracks, lack of fusion, gross porosity, and any imperfections with the following maximum allowable dimensions:

• relevant linear indications exceeding 1,6 mm in transverse direction;
• relevant linear indications exceeding 3,2 mm in longitudinal direction;
• relevant non-linear indications exceeding 4,8 mm.

3.6.5 Surface defects in the region of the flash butt welds may be removed by grinding, provided that the depth of grinding does not exceed five per cent of the link diameter and is smoothly contoured into the surrounding material. The final dimensions are still to conform with the agreed standard.

3.6.6 All flash butt welds on every link are also to be examined by ultrasonic testing in accordance with standards recognised by LR using appropriate scanning techniques designed to detect all expected defects, including any defects within the relevant fusion zones. The flash butt weld must be free from defects causing ultrasonic back reflections equal to or greater than the calibration standard. The single probe technique has limitations as far as testing of the central region is concerned and the flash butt weld imperfections such as flat spots may have poor reflectivity. Where it is deemed necessary, detectability of imperfections may need to be carried out by using a tandem technique, TOFD (Time-of-flight diffraction) or PAUT (phased array ultrasonic testing).

3.6.7 Stud welds, if used, are to be visually inspected. The toes of the fillets are to have a smooth transition to the link with no undercuts exceeding 1,0 mm. In addition, at least 10 per cent of the stud welds distributed through the length is to be magnetic particle or dye penetrant tested in accordance with standards recognised by LR. Cracks, lack of fusion or gross porosity are not acceptable. If defects are found, testing is to be extended to all stud welds in that length of chain.

3.6.8 If a link breaks during proof load testing, a sample consisting of three common links is to be taken from each side of the broken link and subjected to a breaking test as detailed in Ch 10, 3.8 Breaking load tests 3.8.1 and Ch 10, 3.8 Breaking load tests 3.8.2. If either of these samples fails, the proof loaded length of cable is not to be accepted.

3.6.9 In the event that two or more links break during the proof load testing, the proof loaded length is to be rejected.

3.6.10 In all cases when a link breaks during the proof load testing, a thorough examination of all broken links is to be made to determine the cause of failure and, after evaluation, LR will consider the extent of cable which is to be rejected and also the possibility that similar factors to those which caused the failure may also be present in other parts of the cable, or other chain cables, i.e.:

• Where multiple chains are produced simultaneously, it is recognised that the preceding flash butt welded link and subsequent flash butt welded link will be on an alternative chain length or the other end of the chain length. In such cases, LR may require that two additional break tests are to be taken from the lengths of chain that include the preceding and subsequent welded links.
• If the investigation identifies defects in the flash butt weld or a lower strength flash butt weld is found, additional NDE is to be carried out to identify if other links are affected. A full assessment of the flash butt welding machine it to be carried out, together with assessment of the condition of the bar ends prior to welding.
• The Surveyor is to be advised in advance of all examinations, with reasonable notice being given.

3.7.1 After proof testing, the entire chain is to be checked for length, five links at a time with an overlap of two links, which is to include the first five links, to ensure that the chain meets the tolerances given in Ch 10, 3.7 Dimensional inspection 3.7.3. The measurements are to be made while the chain is loaded to about 5-10 per cent of the minimum proof load.

3.7.2 The links held in the end blocks may be excluded from these measurements.

3.7.3  The maximum allowable tolerance on a length of five links measured in accordance with Ch 10, 3.7 Dimensional inspection 3.7.1 is +2,5 per cent. No under-tolerance is permitted.

3.7.4 If the length over five links is less than the nominal, the chain may be stretched by loading above the specified proof test load provided that the applied load is not greater than ten per cent above the proof test load, and that only random lengths of the chain need to be stretched.

3.7.5 Checks of all other dimensions are to be made on at least five per cent of the links in the cable.

3.7.6 A manufacturing tolerance on all other dimensions of ±2,5 per cent is acceptable subject to all parts fitting properly together.

3.7.7 The form and proportions of links are to be in accordance with ISO1704, see Figure 10.2.2 Common link. Link tolerances are to be in accordance with Ch 10, 3.7 Dimensional inspection 3.7.4 to Ch 10, 3.7 Dimensional inspection 3.7.10.

For diameters of 20 mm or greater, the plus tolerance on the diameter at the crown measured perpendicular to the plane of the link, d_p, is not to exceed 5 per cent. For diameters less than 20 mm, the plus tolerance is to be agreed between the chain manufacturer and bar material supplier.

3.7.8  The cross-sectional area at the crown is to be calculated using the average of the measured diameters, which are to be taken from at least two locations approximately 90 degrees apart. The cross-sectional area at the crown is to have no negative tolerance.

3.7.9 The diameter measured at locations other than the crown is to have no negative tolerance. For diameters of 20 mm or greater, the plus tolerance may be up to 5 per cent of the nominal diameter except at the butt weld where it is to be in accordance with the manufacturer’s specification, which is to be agreed by LR. For diameters less than 20 mm, the plus tolerance is to be agreed between the chain manufacturer and bar material supplier.

3.7.10 If any link fails to meet the above dimensional tolerance requirements, measurements are to be made on 20 more links on each side of the incorrect one. If failure to meet any particular dimensional requirements occurs in more than two of the measured links, then all the links are to be dimensionally checked.

3.7.11 Should any link be found to be defective or fail to meet the dimensional tolerance requirements or if a five link length of chain exceeds the specified tolerance, the unsatisfactory links are to be removed from the chain and connecting common links complying with the requirements of Ch 10, 3.10 Connecting common links or substitute links inserted in their places. Proposals for other methods of repair must be subject to approval by LR and the purchaser. Weld repair of chain is not permitted.

3.7.12 The tolerances for common links are to be measured in accordance with Table 10.3.2 Stud link chain cable common link tolerances and Table 10.3.3 Studless link chain cable common link tolerances.

3.7.13 The chain is then to be subjected to a further proof load test and re-examined.

3.7.14 The number of connecting common links which may be used to replace defective links is not to exceed three in any 100m length of chain. The number and type of joining shackles which may be used are to be subject to the written agreement of the end user.

3.7.15 All measurements are to be made on links selected by the Surveyor and are to be carried out to the Surveyor’s satisfaction.

3.7.16 For stud link chain, studs are to be located in the links centrally, and at right angles to the sides of the link, although the studs of the final link at each end of any length may also be located off-centre to facilitate the insertion of the joining shackle. The tolerances in accordance with Table 10.3.2 Stud link chain cable common link tolerances are acceptable provided that the stud fits snugly and its ends lie flush against the inside of the link.

3.7.17 Chain dimensions are to be recorded and the information retained on file.

Table 10.3.2 Stud link chain cable common link tolerances

The internal link radii (R) and external radii should be uniform
Designation	Description	Nominal dimension of the link	Minus tolerance	Plus tolerance
a	Link length	6d	0,15d	0,15d
b	Link half length	a*/2	0,10d	0,10d
c	Link width	3,6d	0,09d	0,09d
e	Stud angular misalignment	0 degrees	4 degrees	4 degrees
R	Inner radius	0,65d	0	—
Symbols
d = nominal diameter of chain a* = actual link length

Table 10.3.3 Studless link chain cable common link tolerances

The internal link radii (R) and external radii should be uniform
Designation	Description	Nominal dimension of the link	Minus tolerance	Plus tolerance
a	Link length	6d	0,15d	0,15d
b	Link width	3,35d	0,09d	0,09d
R	Inner radius	0,60d	0	—
Symbols
d = nominal diameter of chain
Note Other dimensional ratios are subject to special approval.

3.8.1 In addition to the requirements of Ch 10, 3.6 Proof load tests and non-destructive examination 3.6.1, three link samples are to be selected by the Surveyors from the completed chain for breaking tests. The number of tests required is to be in accordance with Ch 10, 3.8 Breaking load tests 3.8.5. Extra links are to be provided for the mechanical tests detailed in Ch 10, 3.9 Mechanical tests 3.9.1. All test links are to be made as part of the chain cable and are to be heat treated with it. These may be removed from the cable prior to heat treatment provided that each sample is heat treated with, and in the same manner as, the chain it represents prior to selection of the mechanical test specimens. They are to be properly identified with the length of chain they represent.

3.8.2 Breaking test specimens are to withstand the load given in Table 10.3.1 Test loads for mooring chain cables for the appropriate grade and size of cable for a period of 30 seconds. The specimen is considered to have passed this test if it has shown no sign of fracture and must not crack in the flash butt weld after application of the required load.

3.8.3 If a breaking test specimen fails, two further specimens are to be cut from the same sampling length and both are to be subjected to the breaking test load. If one of the re-test specimens fails the length is to be rejected. All the broken links are to be subjected to an investigation into the cause of failure. LR will then decide which lengths of chain can be accepted and on further action.

3.8.4 For chain diameters over 100 mm, alternative break-test proposals to the above break-test will be considered whereby a one link specimen is used. Alternatives are to be approved by LR; every heat is to be represented, the test frequency is to be in accordance with Table 10.3.4 Frequency of break and mechanical tests, and it is to be demonstrated that the alternative test represents an equivalent load application to the three link test.

3.8.5 For large diameter cables where the required breaking load is greater than the capacity of the testing machines, special consideration will be given to acceptance of an alternative testing procedure.

3.9.1 One tensile and three sets of Charpy V-notch impact test specimens are to be taken from links cut from the heat treated and proof loaded chain at intervals no greater than those indicated in Table 10.3.4 Frequency of break and mechanical tests provided that every cast is sampled. The tensile specimen and one set of impact specimens are to be taken from the side of the link opposite the weld. One set of impact test specimens is to have the notches positioned at the centre of the flash butt weld and the third set is to be taken from the bend. All the specimens are to be taken from positions in accordance with Figure 10.3.2 Sampling of chain links.

3.9.2 The frequency of testing at the link bends may be reduced at the discretion of LR provided it can be verified that the required toughness is achieved consistently.

3.9.3 The results of the mechanical tests are to comply with the requirements of Table 10.3.5 Mechanical properties of chain cable materials.

3.9.4 If the tensile test requirements are not achieved, two further specimens from the same sample are to be tested. The related length of chain will be considered acceptable if both re-test specimens meet the requirements but failure of either of the re-test specimens will result in rejection of the sampling length of chain represented by the tests.

3.9.5 If the impact test requirements are not achieved, re-tests may be carried out in accordance with Ch 2, 1.4 Re-testing procedures. Failure to meet the re-test requirements will result in rejection of the sampling length of chain represented by the tests.

3.9.6 A grain size determination must be made for the final product. The austenitic grain size for R3, R3S, R4, R4S and R5 is to be 6 or finer in accordance with ASTM E112 or equivalent grain size index in accordance to ISO 643. Measurements for circular sections are to be taken at surface, at one-third of the radius and centre for the base material, HAZ and weld.

3.9.7 Hardness tests are to be carried out on finished chain. The frequency and locations are to be agreed with LR. The recorded values are for information only and used as an additional check to verify that the heat treatment process has been stable during the chain production.

3.9.8 The mass per unit length of stud link mooring cable is to comply with Table 10.3.6 Mass per unit length of stud link chain cable.

Figure 10.3.2 Sampling of chain links

3.10.1 Single links to connect lengths of heat treated chain cable or to substitute for test links or defective links without the necessity for re-heat treatment of the whole length of cable are to be made by the chain manufacturer in accordance with an approved procedure. Separate approvals are required for each grade of chain cable and tests are to be made on the maximum size of chain for which approval is sought.

3.10.2 Manufacture and heat treatment of the connecting common link is not to affect the strength of the adjoining links. The temperature reached by these links is nowhere to exceed 250°C.

3.10.3 The steel bar used is to conform with the specification for the chain and approved by LR in accordance with Ch 3, 9 Bars for welded chain cables.

3.10.4 Details of the method of manufacture, including heat treatment, are to be submitted for approval, together with the results of a series of tests laid down by LR.

3.10.5 All links involved in the approval tests are to be destroyed and are not to be used as part of a chain cable.

3.10.6 Every connecting common link included in a chain cable is to be subjected to the proof load appropriate to the grade and size of chain in which it is incorporated as detailed in Table 10.3.1 Test loads for mooring chain cables.

3.10.7 Every connecting common link is to be inspected in accordance with Ch 10, 3.6 Proof load tests and non-destructive examination 3.6.3.

3.10.8 A second identical link is to be made for mechanical tests which are to be in accordance with Ch 10, 3.9 Mechanical tests 3.9.1. This test link is also to be inspected in accordance with Ch 10, 3.10 Connecting common links or substitute links 3.10.7.

3.10.9 Each connecting common link is to be stamped with the identification marks listed in Ch 10, 3.11 Identification 3.11.1 plus a unique number for the link. The adjoining links are also to be stamped.

3.11.1 Each length of chain is to be permanently marked with the following:

1. LR and abbreviated name of LR's local office issuing the certificate.

2. Certificate number (this may be abbreviated provided it is stated in the certificate).

3. Grade and proof load of chain.

3.11.2 The chain is to be marked as follows:

1. at each end (the marking should identify the leading and tail end of each chain),

2. at intervals not exceeding 100 m,

3. on all connecting common links or shackles and the immediately adjacent links,

4. on the first and last common link of each individual heat used in the continuous length.

3.11.3 All identification marks are to be made on the studs for stud link chain or, on the outside of the straight part of the link, opposite the flash butt weld for studless chain, and are to be permanent and legible throughout the expected service life of the chain.

3.12.1 A complete Chain Inspection and Testing Report, in booklet form, is to be provided by the chain manufacturer for each continuous chain length, and for each order for chain and fittings. It is to include all dimensional checks, test and inspection reports, non-destructive test reports, process records, photographs (for fittings, example photographs of components positioned in furnaces), as well as any non-conformity, together with corrective action and repair work.

3.12.2 All documents, including reports and appendices, are to contain a reference to the relevant certificate number.

3.12.3 The chain manufacturer is responsible for storing all the documentation in a safe and retrievable manner for a period of at least 10 years.

3.13.1 An LR certificate is to be issued for each continuous single length of chain, and each type of fitting, see Ch 1, 3.1 General.

3.13.2 Each test certificate is to include the following particulars:

1. Purchaser’s name and order number.

2. Description and dimensions.

3. Grade of chain cable.

4. Identification mark which will enable the full history of the chain to be traced.

5. Chemical composition.

6. Details of heat treatment.

7. Mechanical test results.

8. Breaking test load.

9. Proof load.

10. The number and locations of all connecting common links and all marked links.