DNV CP 0237

CLASS PROGRAMME
Approval of manufacturers
DNV-CP-0237 Edition September 2021
Offshore mooring chain and accessories
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DNV AS
FOREWORD
DNV class programmes contain procedural and technical requirements including acceptance
criteria for obtaining and retaining certificates for objects and organisations related to
classification.
© DNV AS September 2021
Any comments may be sent by e-mail to rules@dnv.com
This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this
document. The use of this document by other parties than DNV is at the user's sole risk. DNV does not accept any liability or responsibility
for loss or damages resulting from any use of this document.
CHANGES – CURRENT
Changes - current
This document supersedes the July 2018 edition of DNVGL-CP-0237.
The numbering and/or title of items containing changes is highlighted in red.
Changes September 2021
Topic Reference Description
Rebranding to DNV All This document has been revised due to the rebranding of DNV
GL to DNV. The following have been updated: the company
name, material and certificate designations, and references to
other documents in the DNV portfolio. Some of the documents
referred to may not yet have been rebranded. If so, please see
the relevant DNV GL document. No technical content has been
changed.
Editorial corrections
In addition to the above stated changes, editorial corrections may have been made.
Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 3

DNV AS
CONTENTS
Contents
Changes – current.................................................................................................. 3
Section 1 General.................................................................................................... 5
1 Scope................................................................................................... 5
2 Range of approval............................................................................... 5
3 Validity and renewal............................................................................5
4 Extension of approval.......................................................................... 5
5 Approval procedure, general............................................................... 6
6 References........................................................................................... 7
Section 2 Approval procedure, chain cables............................................................8

1 General................................................................................................ 8
2 Range of approval............................................................................... 8
3 Approval information........................................................................... 8
4 Approval testing, chain...................................................................... 11
5 Approval testing, accessories............................................................ 14
Section 3 Approval procedure, steelmaking and rolled steel products.................. 17

1 General.............................................................................................. 17
2 Range of approval............................................................................. 17
3 Approval information......................................................................... 17
4 Approval testing, round bars............................................................. 17
5 Approval testing, ingots, blooms and billets...................................... 19
Section 4 Approval procedure, steel forgings....................................................... 20

1 General.............................................................................................. 20
4 Approval testing................................................................................ 20
Section 5 Approval procedure, steel castings....................................................... 22

1 General.............................................................................................. 22
4 Approval testing................................................................................ 22
Changes – historic................................................................................................ 24

DNV AS
SECTION 1 GENERAL
Section 1
1 Scope
This programme gives the procedure to be followed to obtain the Society's approval for the manufacture of
offshore mooring chain, chain cable accessories and starting materials in accordance with the requirements
of DNV-OS-E302.
2 Range of approval
Available approval categories and associated product categories for which approval is required are listed in
Table 1 and briefly described. Requirements and limitations are detailed in Sec.2 to Sec.5.
Table 1 Approval categories and product categories
Approval category Product category Brief description
Offshore mooring chain Approval required for each grade and product.
Approval limited to nominated supplier of rolled,
Chain cables forged or cast material, as applicable.
Forged or cast chain cable accessories Max. approved diameter or thickness limited to tested
-diameter or thickness.
Approval required for each grade.

Steelmaking and Round bars for chain cables
Max. approved diameter limited to tested diameter.
rolled steel products
Ingots, blooms and billets for chain cables Approval required for each grade.
Approval required for each grade.

1) Approval limited to nominated manufacturer of
Steel forgings Forgings for chain cable accessories
starting material.
1) Approval required for each grade.

Steel castings Castings for chain cable accessories
1)
Approval category chain cables apply if forging manufacturers and foundries supply finished chain cable accessories.
3 Validity and renewal

The approval will be valid for three years. To maintain the approved status, the manufacturer shall be re-
inspected every three years. Application for renewal should be made not later than three months before the
expiry date of the certificate.
Any essential changes made to the manufacturing process, equipment or procedures during the period of
validity shall be reported to the Society. A re-inspection and/or re-testing may be required when deemed
necessary by the Society.
4 Extension of approval
An existing approval may be extended or changed with respect to range of approval, see Table 1.
The approval procedure given in [5] generally applies. However, reduced testing and/or documentation may
be agreed where this is proposed. In such cases, the proposals shall contain relevant technical justifications.

DNV AS
Section 1
5 Approval procedure, general
5.1 Application
Application for approval shall be sent to the local DNV office with the following information:
— Name and address of the manufacturer’s works.
— Product, grade, condition of supply/heat treatment and maximum diameter/size for which approval is
requested.
— A brief description of manufacturing, testing and inspection facilities and equipment. The description need
not be re-submitted in connection with application for extension of an existing approval unless changes
have taken place.
5.2 Works inspection

After receipt and review of the application the surveyor will carry out a works inspection to verify that the
necessary manufacturing, testing, and inspection facilities are available and that the activities are supervised
by qualified personnel.
Products shall be subjected to approval testing as described in Sec.2 to Sec.5. Approval testing carried out by
the manufacturer shall be witnessed by the surveyor, unless otherwise described in Sec.2 to Sec.5. Approval
testing carried out by recognised laboratories need not be witnessed.
The surveyor may request additional documentation in preparation for the works inspection, if deemed
necessary.
5.3 Approval testing

Products shall be subjected to approval testing as described in Sec.2 to Sec.5. Approval testing carried out by
the manufacturer shall be witnessed by the surveyor, unless otherwise described in Sec.2 to Sec.5. Approval
testing carried out by recognised laboratories need not be witnessed.
Unless otherwise specified herein, the preparation and location of test pieces, the testing procedures, and the
test results shall comply with the relevant requirements in DNV-OS-E302.
Where valid tests fail to meet specified requirements, the manufacturer shall assess the need for changes
to materials or processes and, if necessary, implement the changes. Retesting without any changes
implemented will only be accepted subject to satisfactory technical justification.
5.4 Submission of approval report

On completion of approval testing, the manufacturer shall submit a complete approval report to the local DNV
office. The report shall contain the approval information and the results from approval testing specified in
Sec.2 to Sec.5. The report shall be signed and dated by the manufacturer’s representative.
The English language shall be used in the documentation. To facilitate evaluation of the report, it should be
well organised, preferably by using the same order and indexing as described in this programme.
5.5 Evaluation of approval report

When received at the local DNV office, the approval report will be checked for completeness and then
forwarded to DNV Høvik for evaluation together with applicable checklists.

DNV AS
Section 1
5.6 Issue of approval of manufacturers certificate
Manufacturers whose works have been inspected and whose approval report has been reviewed with
satisfactory result will be granted an approval of manufacturers certificate. Valid DNV certificates are listed in
DNV approval finder on DNV's web site www.dnv.com.
5.7 Suspension and withdrawal of approval of manufacturers certificate

All or part of a manufacturer’s scope of approval will be suspended or subsequently withdrawn when it is
found that the manufacturer is no longer meeting the requirements for approval and identified issues are not
adequately responded to and rectified within a defined time-frame. In these circumstances, the manufacturer
will be notified in writing.
6 References
Table 2 Normative references
Document code Title
DNV-OS-E302 Offshore mooring chain
Metallic materials - Unified method of test for the determination of quasistatic fracture
ISO 12135
toughness
Standard practice for slow strain rate testing to evaluate the susceptibility of metallic
ASTM G129
materials to environmentally assisted cracking
ASTM D1141 Standard practice for the preparation of substitute ocean water
ASTM E1820 Standard test method for measurement of fracture toughness

DNV AS
SECTION 2 APPROVAL PROCEDURE, CHAIN CABLES
Section 2
1 General
This section is supplementary to Sec.1 and applies to manufacturers of offshore mooring chain and
accessories.
2 Range of approval
— Approval is required for each grade.
— Approval for a higher grade, e.g. R4, may cover a lower grade, e.g. R3S, provided that the same material
specification and manufacturing processes are used. Grade(s) approved on this basis will be included in
the approval certificate.
— Approval is required for each product category. Approval for chain does not cover accessories or vice
versa.
— Approval is required for each type of chain. Approval for stud link chain does not cover studless chain or
vice versa.
— Max. approved diameter or thickness is limited to tested diameter or thickness. For chain, the approved
diameter is related to nominal chain diameter and also covers enlarged and end links. For chain
accessories, the approved diameter or thickness is related to nominal chain accessory diameter or
thickness.
— Approval is limited to a nominated manufacturer of rolled, forged or cast material. Where material from a
number of suppliers is used, separate approval is required for each supplier.
3 Approval information
3.1 Manufacturing summary

The manufacturer shall establish and submit a manufacturing summary (or manufacturing procedure
specification) for each product, grade and size range. Several grades and/or size ranges can be combined
into one manufacturing summary where this is convenient.
The manufacturing summary shall specify the sequence of all important manufacturing process steps
and the conditions for control, e.g. by reference to instructions or procedures. Any supply of materials or
subcontracted activities shall be identified and the names of suppliers/subcontractors given.
Where a manufacturer applies for extension of an existing approval to cover larger diameters, new supplier of
starting material, etc., the manufacturing summary shall be updated accordingly.
Guidance note:
The format of the manufacturing summary may be a table consisting of three columns. First column should contain a listing of the
process steps, second column should contain identification of the procedure/instruction and third column should contain a brief
description of the process steps.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
The manufacturing summary shall include, but not necessarily be limited to, the process steps given in Table
1.
Table 1 Content of the manufacturing summary
No. Manufacturing summary, chain Manufacturing summary, accessories
For forged accessories: Starting material, heating/

1 Starting material
reheating and forging

DNV AS
No. Manufacturing summary, chain Manufacturing summary, accessories
Section 2
For cast accessories: Moulding, melting, refining and
2 Cutting, heating and forming of blanks
pouring, repair by welding
3 Flash butt welding and removal of excess material Heat treatment
4 Stud insertion and welding, if applicable Machining, if relevant
5 Stud pressing, if applicable Proof load, breaking load and mechanical testing
6 Heat treatment Blasting/cleaning
7 Proof load, breaking load and mechanical testing Measurements, visual inspection and NDT
8 Blasting/cleaning Repair
9 Measurements, visual inspection and NDT Identification
10 Repair
11 Identification
3.2 Specification for chemical composition, chain and accessories

This shall be submitted if it is tighter than the steel suppliers’ specification, i.e. in case of narrower ranges
and/or lower maximum limits for elements. See Sec.3 [3.1] (rolled steel), Sec.4 [3.1] (forgings) and Sec.5
[3.1] (castings).
3.3 Procedures for manufacturing and testing

Procedures shall be established and submitted for the manufacturing and testing activities given in Table 2
for chain and Table 3 for accessories, respectively.
Table 2 Procedures for manufacture and testing of chain
Procedure for activity Minimum details to be contained in procedure
— Chain grade, base material.

— Welding method, position, consumable, preheat temperature.
Stud welding, if applicable — Electrical characteristics, travel speed/heat input, size of weld.
— Visual inspection, NDT.
— Records.
— Type of equipment, capacity.

Stud pressing, if applicable — Press arrangement, loads, load control.
— Records.
— Type of furnace, heating method, temperature controls.

— Furnace entry: stabilization, arrangement of scrap chain.
— Heat treat cycle: furnace zone set temperatures, travel speed.
Heat treatment
— Quenching: water temperature, agitation, temperature control.
— Cooling after tempering: water temperature.
— Identification, traceability, records.

DNV AS
Section 2
— Test machines/type of equipment, calibrations.
Proof load and breaking load testing — Testing arrangement, applicable loads, load control.
— Test machines, calibrations.

Mechanical testing — Reference to DNV-OS-B101 as test standard.
— Type of furnace/fixture, heating method, temperature controls.

— Arrangement of splice link and adjacent links, insulation of splice link or
adjacent links, thermocouples attached to links.
— Heat treat cycle: set temperatures with tolerances, holding times.
— Furnace/fixture unloading: method, removal of insulation, max. transfer
time from furnace/fixture to entry in quench tank.
Splice link, if applicable — Quenching: water temperature, agitation, temperature control, holding
time in tank.
— Cooling after tempering: water temperature, holding time in tank.
— Testing and inspection.
The procedure shall be accompanied by results from procedure tests, see
[4.10].
— Type of equipment, calibrations.

— Dimensions to be measured.
Dimensional inspection
— Extent of measurements.
— Records.
NDT procedures shall contain the details specified in the applicable reference
Visual inspection and NDT
standards given in DNV-OS-E302.
Table 3 Procedures for manufacture and testing of accessories
— Starting material grade and type, e.g. ingot/billet/bar.

— Heating temperatures, holding times, temperature controls.
— Forging method, forging reduction, sequence of forging steps, forging
Forging (forged accessories)
temperature range, temperature control.
— Cleaning/de-scaling, inspection.
Welding procedures shall contain the details specified in the applicable

Repair by welding (cast accessories)
reference standards given in DNV-OS-E302.

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Section 2
— Type of furnace, heating method, temperature controls.
— Furnace loading: loading temperature, arrangement of parts, distance
between parts, thermocouples attached to parts.
— Heat treat cycle: set temperatures with tolerances, holding times.
— Furnace unloading: method, max. transfer time from furnace to entry in
Heat treatment quench tank.
— Quenching: water temperature, agitation, temperature control, holding
time in tank.
— Cooling after tempering: cooling medium, temperature, holding time in
tank.
— Test machines/type of equipment, calibration.

Proof load and breaking load testing — Testing arrangement, applicable loads, load control.
— Test machines, calibration.

— Reference to DNV-OS-B101 as test standard.
Mechanical testing — Sketches of test material, e.g. sacrificial accessories, showing the position
of test pieces.
— Type of equipment, calibration.

— Dimensions to be measured.
Dimensional inspection
— Extent of measurements.
— Records.
NDT procedures shall contain the details specified in the applicable reference
Visual inspection and NDT
standards given in DNV-OS-E302.
4 Approval testing, chain
4.1 Test material

One length of chain with a sufficient number of links shall be manufactured and subjected to the tests
detailed in [4.3] to [4.10]. The bar material used shall be from at least one heat of steel.
4.2 Manufacturing records

Records or data for the manufacture of the test chain shall be part of the approval report and include:
— Bar material certificate. Where multiple heats are covered, the heat used shall be identified.
— Heating of blanks and flash butt welding.
— Heat treatment and check of furnace temperature uniformity.
— Proof load testing.
— Measurement of dimensions.
— Visual inspection, magnetic particle and ultrasonic testing.

DNV AS
Section 2
4.3 Proof load and breaking load testing
At least two samples shall be tested.
4.4 Tensile and impact testing

— At least three links shall be tested.
— From each link, two tensile and nine Charpy V-notch impact test pieces shall be taken. The extra tensile
test piece shall be taken across the flash weld.
— Impact test temperature shall be -20°C.
— Elongation and reduction of area in the cross-weld tensile test are for information only.
4.5 CTOD testing

— At least three links shall be tested. The links for tensile and impact testing may be used.
— From each link, two test pieces shall be taken: one across the flash weld with the crack tip accurately
located in the seam, and one from the opposite side. See Figure 1.
— Testing shall be in accordance with a recognised standard, e.g. ISO 12135, using a standard 2 × 1 single
edge notched bend piece.
— The minimum test piece size shall be 50 mm × 25 mm for chain diameters less than 120 mm, and 80 mm
× 40 mm for diameters 120 mm and above.
— Test temperature shall be -20°C.
— The lowest value for 3 to 5 valid results shall comply with requirements given in Table 1. Where 6 to 10
valid results are available, the second lowest value applies.
Table 4 CTOD minimum values in mm
R3 R3S R4 R4S and R5 R6

Chain type
Base Weld Base Weld Base Weld Base Weld Base Weld
Stud link 0.10 0.11 0.12 0.13 0.14

0.20 0.22 0.24 0.26 0.27
Studless 0.14 0.15 0.16 0.17 0.18
Figure 1 Position of CTOD test pieces. The test pieces should be located as close as possible to the
surface

DNV AS
Section 2
Figure 2 Sectioning of link and measurements of stud imprints
4.6 Hardness testing, quenched and tempered (QT) condition

— At least one link shall be tested.
— The hardness distribution shall be determined along a diameter clear of the weld using Vickers or Rockwell
indentors.
— The hardness at the centre shall not be less than 85% of the hardness at one-third of the radius from the
surface.
— The hardness distribution should be presented as a diagram with indication of centre and one-third radius
positions.
4.7 Stud imprint examination, stud link chain

— At least one link shall be examined for proper stud imprints on the weld side and opposite side.
— The link shall be sectioned as indicated in Figure 2.
— Prior to centreline sectioning, the imprints shall be photographed and measurements made of length,
width and corner radius.
— The centreline sections shall be photographed and measurements made of imprint depth and radius.
— Photographs and measurement results shall be submitted.
4.8 Slow strain rate testing of R4S and R5

Additional requirements for grade R4S and R5 include slow strain rate testing to evaluate the resistance to
environmentally assisted cracking. Unless otherwise agreed or required, the following conditions apply:
— At least two links shall be tested. The links for tensile and impact testing may be used.
— From each link, two test pieces shall be prepared from the side opposite the weld as close as possible to
the surface.
— Testing shall be in accordance with ASTM G129 or an equivalent standard using uniaxial smooth tension
test pieces.
— Testing shall be in artificial seawater according to ASTM D1141 and in dry air (control environment),
respectively.
-5 -1
— Testing shall be performed at a strain rate of 10 [s ]. Testing at lower rates is acceptable.
— Test results shall be reported as reduction in area after fracture including reduction in area ratio.
— Evaluation of cracking resistance will be based on the reduction in area ratio but acceptance criteria have
not been established.
4.9 Environmentally assisted cracking tests for R6

Additional requirements for grade R6 include slow strain rate testing to evaluate the resistance to

DNV AS
— From each link, two test pieces for each test condition shall be prepared from the side opposite the weld
Section 2
(base material) and across the weld as close as possible to the surface.
test pieces.
— Testing shall be performed under the following conditions: in artificial seawater according to ASTM D1141
at free corrosion potential, at applied potential -850 mV (SCE), at applied potential -1200 mV (SCE) and
in dry air (control environment).
-5 -1
In addition, KIEAC testing shall be performed. Unless otherwise agreed or required, the following conditions
apply:
— From each link, two test pieces for each test condition shall be prepared from the side opposite the weld
(base material) and across the weld.
— Testing shall be in accordance with ASTM E1820 or an equivalent standard using compact tension
specimens with thickness 25 mm.
at applied potential -950 mV (SCE) and at applied potential -1050 mV (SCE).
— Specimens shall be hydrogen pre-charged for 48 hours prior to testing.
-9
— Testing shall be performed at a rate of 6 10 m/s. Testing at lower rates is acceptable.
— Test results shall be reported as KIEAC values indicating the sensitivity to the environment.
4.10 Splice link procedure testing

— At least one splice link and one adjacent link shall be tested after proof load testing.
— From each splice link, one tensile and nine Charpy V-notch impact test pieces shall be taken.
— From each adjacent link, three Charpy V-notch impact test pieces shall be taken from the outer bend
region.
— Results of dimensional measurements and NDT examination after proof load testing shall be submitted.
The range of approval for splice links is the same as for chain, see [2].
5 Approval testing, accessories
5.1 Test material

A sufficient number of accessories shall be manufactured and subjected to the tests detailed in [5.3] to [5.7].
Unless otherwise specified herein, the preparation and location of test pieces, the testing procedures, and the
test results shall comply with the relevant requirements in DNV-OS-E302.

Records or data for the manufacture of the test accessories shall be part of the approval report and include:
— Starting material certificate. Where multiple heats are covered by the certificate, the heat used shall be
identified.
— Forging or casting, as relevant.
— Heat treatment and check of furnace temperature uniformity.

DNV AS
— Proof load testing.
Section 2
— Measurement of dimensions.
— Visual inspection, magnetic particle and ultrasonic testing.
5.3 Proof load and breaking load testing

At least one accessory shall be tested.
5.4 Tensile and impact testing

— For conventional accessories such as Kenter and D-shackles, at least two accessories shall be tested.
— For accessories of unconventional design and/or large sections, at least one accessory shall be tested. This
is subject to prior agreement and it does not apply to grade R4S, R5 and R6.
— From each accessory, one tensile and three Charpy V-notch impact test pieces shall be taken.
5.5 CTOD testing

— At least one accessory or representative coupon shall be tested. The accessories for tensile and impact
testing may be used.
— Testing may be waived for grade R3, R3S and R4 provided it is justified and agreed in advance.
— Three test pieces shall be taken.
— Testing shall be in accordance with a recognised standard, e.g. ISO 12135, using a standard 2 × 1 single
edge notched bend piece.
— The minimum test piece size shall be 50 mm × 25 mm for diameters less than 120 mm, and 80 mm × 40
mm for diameters 120 mm and above.
— Test temperature shall be -20°C.
— The lowest value for 3 valid results shall comply with requirements given for base material in Table 4.
5.6 Slow strain rate testing of R4S and R5

Additional requirements for grade R4S and R5 include slow strain rate testing to evaluate the resistance to
— At least one accessory shall be tested. The accessory for tensile and impact testing may be used.
— Two test pieces shall be prepared as close as possible to the surface.
test pieces.
— Testing shall be in artificial seawater according to ASTM D1141 and in dry air (control environment),
respectively.
-5 -1
5.7 Environmentally assisted cracking tests for R6

Additional requirements for grade R6 include slow strain rate testing to evaluate the resistance to
— Two test pieces for each test condition shall be prepared as close as possible to the surface.

DNV AS
Section 2
test pieces.
at free corrosion potential, at applied potential -850 mV (SCE), at applied potential -1200 mV (SCE) and
in dry air (control environment).
-5 -1
In addition, KIEAC testing shall be performed. Unless otherwise agreed or required, the following conditions
apply:
— Two test pieces for each test condition shall be prepared.
— Testing shall be in accordance with ASTM E1820 or an equivalent standard using compact tension
specimens with thickness 25 mm.
at applied potential -950 mV (SCE) and at applied potential -1050 mV (SCE).
— Specimens shall be hydrogen pre-charged for 48 hours prior to testing.
-9
— Testing shall be performed at a rate of 6 10 m/s. Testing at lower rates is acceptable.
— Test results shall be reported as KIEAC values indicating the sensitivity to the environment.

DNV AS
SECTION 3 APPROVAL PROCEDURE, STEELMAKING AND ROLLED
Section 3
STEEL PRODUCTS
1 General
This section is supplementary to Sec.1 and applies to manufacturers of round bars, ingots, blooms and billets
for chain cables.
2 Range of approval
— Approval is required for each product category. For integrated steelworks, approval for round bars covers
semi-finished products, e.g. blooms, but not vice versa.
— Approval is required for each melting and casting process.
— Max. approved bar diameter is limited to tested diameter.
— For rolling mills without own steelmaking facilities, approval is limited to a nominated steelmaker. Where
material from a number of suppliers is used, separate approval is required for each supplier.
3.1 Specification for chemical composition

The specification for chemical compositon shall include, but not necessarily be limited to:
— permissible range for carbon, manganese, silicon and all other intentionally added elements, e.g.
chromium, molybdenum, nickel, aluminium, niobium, vanadium, titanium
— maximum limits for residual and impurity elements including phosphorus, sulphur, copper (unless added),
tin, antimony, arsenic, boron
— maximum limit for nitrogen.
4 Approval testing, round bars
4.1 Test material

One or more bars shall be manufactured and subjected to the tests detailed in [4.3] to [4.7]. The bar(s) shall
originate from the tail end of the string in case of continuous casting, and from the top of the ingot in case of
ingot casting.

Records or data for the manufacture of the test bars shall be part of the approval report and include:
— steelmaking, refining, and casting
— chemical composition
— reheating and rolling, including rolling reduction ratio
— hydrogen degassing treatment, if used
— for R4S, R5 and R6, examination for non-metallic inclusions, macro etching for segregation, and testing
for hardenability

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— heat treatment condition for test material
Section 3
— measurements, visual inspection and NDT.
4.3 Heat treatment sensitivity study, QT condition

A heat treatment sensitivity study simulating chain or accessory production conditions shall be applied in
order to check the candidate material’s sensitivity to deviations from a target (optimum) heat treatment
route. It is thus essential that the target (optimum) heat treatment is performed in a manner simulating
realistic conditions for chain or accessory manufacture. At least nine samples of full cross section shall be
heat treated and subjected to tensile and Charpy V-notch testing. Unless otherwise agreed or required, the
heat treat conditions given in Table 1 apply for the samples.
Table 1 Heat treatment sensitivity study parameters for rolled steel products
Austenitisation Tempering
No.
Temperature [°C] Time [minutes] Temperature [°C] Time [minutes]
1 Ac3 + 30 30 610 60
2 Ac3 + 60 30 610 60
3 Ac3 + 90 30 610 60
4 Ac3 + 60 60 610 60
5 Ac3 + 60 30 570 60
6 Ac3 + 60 30 590 60
7 Ac3 + 60 30 650 60
8 Ac3 + 60 30 610 30
9 Ac3 + 60 30 610 90
4.4 Mechanical testing, material intended for normalising

— For chain or accessories supplied in the normalised condition, at least one sample of full cross section shall
be heat treated and subjected to tensile and Charpy V-notch testing.
4.5 Temper embrittlement testing, QT condition

The material’s resistance to temper embrittlement shall be tested. At least two samples of full cross section
shall be heat treated and subjected to Charpy V-notch testing. Unless otherwise agreed or required, the
following heat treat conditions apply for the samples:
— Austenitisation at Ac3 + 60°C for 30 minutes. Tempering at 570°C for 60 minutes. Rapid cooling in water.
— Austenitisation at Ac3 + 60°C for 30 minutes. Tempering at 570°C for 60 minutes. Slow cooling inside
furnace for at least 40 minutes down to 300°C.
— Test temperatures shall be 0°C, -20°C and -40°C.
— The specified minimum properties at -20°C shall be met.

DNV AS
Section 3
4.6 Strain age testing
— The material’s resistance to strain aging shall be tested. At least one sample of sufficient size shall be heat
treated, strained 5% and subsequently heated to 100°C and held for one hour.
— Charpy V-notch testing shall be carried out at 0°C, -20°C and -40°C.
4.7 Hydrogen embrittlement testing

For R3S, R4, R4S, R5 and R6, at least one sample shall be tested.
5 Approval testing, ingots, blooms and billets
5.1 Test material

Where manufacturers supply semi-finished products to rolling mills or forges, one or more products shall be
manufactured and subjected to the tests detailed for round bars or forgings, as applicable.
Separate approval testing of semi-finished products is not required.

Records or data for the manufacture of the test products shall be part of the approval report and include:
— steelmaking, refining, and casting
— reheating and rough rolling, if applicable
for hardenability.

DNV AS
SECTION 4 APPROVAL PROCEDURE, STEEL FORGINGS
Section 4
1 General
This section is supplementary to Sec.1 and applies to manufacturers of steel forgings for chain cable
accessories. The approval procedure applicable to finished chain cable accessories is given in Sec.2.
2 Range of approval
— Max. approved diameter is limited to tested diameter.
— Approval is limited to a nominated manufacturer of starting material. Where material from a number of
suppliers is used, separate approval is required for each supplier.

The specification for chemical composition shall include, but not necessarily be limited to:
— permissible range for carbon, manganese, silicon and all other intentionally added elements, e.g.
chromium, molybdenum, nickel, aluminium, niobium, vanadium, titanium
— maximum limits for residual and impurity elements including phosphorus, sulphur, copper (unless added),
tin, antimony, arsenic, boron
— maximum limit for nitrogen.
4 Approval testing
4.1 Test material

One or more forgings shall be manufactured and subjected to the tests detailed in [4.3] to [4.7].

Records or data for the manufacture of the test forgings shall be part of the approval report and include:
— starting material supplier, product form and dimensions
for hardenability
— heating/reheating and forging, including forging reduction ratio
— heat treatment

A heat treatment sensitivity study simulating production conditions shall be applied in order to check the
candidate material’s sensitivity to deviations from a target (optimum) heat treatment route. It is thus

DNV AS
essential that the target (optimum) heat treatment is performed in a manner simulating realistic conditions
Section 4
for accessory manufacture. At least seven samples of full cross section shall be heat treated and subjected to
tensile and Charpy V-notch testing. Unless otherwise agreed or required, the heat treat conditions given in
Table 1 apply for the samples.
Table 1 Heat treatment sensitivity study parameters for steel forgings and castings
Austenitisation Tempering
No.
Temperature [°C] Time [minutes] Temperature [°C] Time [minutes]
1 Ac3 + 30 60 610 60
2 Ac3 + 60 60 610 60
3 Ac3 + 90 60 610 60
4 Ac3 + 60 60 590 60
5 Ac3 + 60 60 650 60
6 Ac3 + 60 60 590 120
7 Ac3 + 60 60 650 120

— For forgings supplied in the normalised condition, at least one sample of full cross section shall be heat
treated and subjected to tensile and Charpy V-notch testing.



For R4S, R5 and R6, at least one sample shall be tested. See DNV-OS-E302 Ch.2 Sec.1 [2.6] for details.

DNV AS
SECTION 5 APPROVAL PROCEDURE, STEEL CASTINGS
Section 5
1 General
This section is supplementary to Sec.1 and applies to manufacturers of steel castings for chain cable
accessories. The approval procedure applicable to finished chain cable accessories is given in Sec.2.
2 Range of approval
— Max. approved diameter is limited to tested diameter.

The specification for chemical composition shall include, but not necessarily be limited to:
— Permissible range for carbon, manganese, silicon and all intentionally added added elements, e.g.
chromium, molybdenum, nickel, aluminium, niobium, vanadium, titanium.
— Maximum limits for residual and impurity elements including phosphorus, sulphur, copper (unless added),
tin, antimony, arsenic, boron.
— Maximum limit for nitrogen.
4 Approval testing
4.1 Test material

One or more castings from one heat of steel shall be manufactured and subjected to the tests detailed in
[4.3] to [4.7].

Records or data for the manufacture of the test castings shall be part of the approval report and include:
— moulding, melting, refining and pouring
— repair by welding
for hardenability
— heat treatment

A heat treatment sensitivity study simulating production conditions shall be applied in order to check the
candidate material’s sensitivity to deviations from a target (optimum) heat treatment route. It is thus
essential that the target (optimum) heat treatment is performed in a manner simulating realistic conditions

DNV AS
for accessory manufacture. At least seven samples of full cross section shall be heat treated and subjected to
Section 5
tensile and Charpy V-notch testing. Unless otherwise agreed or required, the heat treat conditions given in
Table 1 apply for the samples.

— For castings supplied in the normalised condition, at least one sample of full cross section shall be heat
treated and subjected to tensile and Charpy V-notch testing.



For R4S, R5 and R6, at least one sample shall be tested. See DNV-OS-E302 Ch.2 Sec.1 [2.6] for details.

DNV AS
CHANGES – HISTORIC
Changes – historic
July 2018 edition
This document replaces the October 2013 edition of DNV-STC-AoM-316.
Changes July 2018

Topic Reference Description
General update. Sec.1 [3] Updated clause, approval validity reduced to 3 years.
Sec.2 [3.1] Updated clause, new guidance note.
Sec.2 [3.3] Updated clause, new information.
Alignment to revised IACS Sec.2 [3.1] Updated clause, alternative manufacturing procedure
W22 on Offshore Mooring specification.
Chain (rev. 6 June 2016).
Sec.2 [4.5] Updated clause, clarification on crack tip opening displacement
(CTOD) testing.
Sec.2 [5.5] Updated clause, new requirement.
Introduction of R6 material Sec.2 [4.9] New environmentally assisted cracking tests for R6 (chain).
grade.
Sec.2 [5.7] New environmentally assisted cracking tests for R6
(accessories).
Sec.2 Table 4 New CTOD values for R6.

DNV AS
About DNV
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CLASS PROGRAMME

Offshore mooring chain and accessories

© DNV AS September 2021

Any comments may be sent by e-mail to rules@dnv.com

Changes September 2021

Topic Reference Description

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 3

Section 2 Approval procedure, chain cables............................................................8

Section 3 Approval procedure, steelmaking and rolled steel products.................. 17

Section 4 Approval procedure, steel forgings....................................................... 20

Section 5 Approval procedure, steel castings....................................................... 22

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 4

Table 1 Approval categories and product categories

Approval category Product category Brief description

Approval required for each grade.

Approval required for each grade.

1) Approval required for each grade.

3 Validity and renewal

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 5

5.2 Works inspection

5.3 Approval testing

5.4 Submission of approval report

5.5 Evaluation of approval report

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 6

5.7 Suspension and withdrawal of approval of manufacturers certificate

Document code Title

DNV-OS-E302 Offshore mooring chain

ASTM E1820 Standard test method for measurement of fracture toughness

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 7

3.1 Manufacturing summary

Table 1 Content of the manufacturing summary

No. Manufacturing summary, chain Manufacturing summary, accessories

For forged accessories: Starting material, heating/

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 8

3 Flash butt welding and removal of excess material Heat treatment

4 Stud insertion and welding, if applicable Machining, if relevant

6 Heat treatment Blasting/cleaning

9 Measurements, visual inspection and NDT Identification

3.2 Specification for chemical composition, chain and accessories

3.3 Procedures for manufacturing and testing

Table 2 Procedures for manufacture and testing of chain

Procedure for activity Minimum details to be contained in procedure

— Chain grade, base material.

— Type of equipment, capacity.

— Type of furnace, heating method, temperature controls.

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 9

— Test machines, calibrations.

— Type of furnace/fixture, heating method, temperature controls.

— Type of equipment, calibrations.

Table 3 Procedures for manufacture and testing of accessories

Procedure for activity Minimum details to be contained in procedure

— Starting material grade and type, e.g. ingot/billet/bar.

Welding procedures shall contain the details specified in the applicable

Class programme: Approval of manufacturers — DNV-CP-0237. Edition September 2021 Page 10

— Test machines/type of equipment, calibration.

— Test machines, calibration.

— Type of equipment, calibration.

4 Approval testing, chain

4.1 Test material