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Sec.1: Materials [Table of Contents] B: Rolled Steel Bars

DNV-OS-E302 Offshore Mooring Chain

[-] Ch.2: Technical Provisions
[-] Sec.1: Materials
[-] A: General Requirements

Ch.2 Sec.1
A. General Requirements

Ch.2 Sec.1
A 100   Scope

Ch.2 Sec.1 A
101   Sub-section A specifies the general requirements for rolled steel bars, steel forgings and steel castings to be used in the manufacture of offshore mooring chain and accessories. Specific requirements are given in B to D. If the specific requirements differ from these general requirements, the specific requirements shall prevail. Separate requirements for materials for studs are given in E.

Ch.2 Sec.1 A
102   The steels concerned are classified by specified minimum ultimate tensile strength into five grades: R3, R3S, R4, R4S and R5.

Ch.2 Sec.1
A 200   Manufacture

Ch.2 Sec.1 A
201   The steels shall be manufactured by an electric or one of the basic oxygen processes or any other approved process involving secondary refining. Steel grades R4S and R5 shall be vacuum degassed.

Ch.2 Sec.1 A
202   The steels shall be killed and fine grain treated. The austenite grain size shall be 5 or finer in accordance with ASTM E112. The fine grain size requirement shall be deemed to be fulfilled if the steels contain Al, Nb, V or Ti, either singly or in any combination, as follows: When Al is used singly, the minimum total content shall be 0.020% or, alternatively, the Al to N ratio shall be minimum 2:1. When Al and Nb are used in combination, the minimum total Al content shall be 0.015% and the minimum Nb content shall be 0.010%. When Al and V are used in combination, the minimum total Al content shall be 0.015% and the minimum V content shall be 0.030%.

Ch.2 Sec.1 A
203   For steel grades R4S and R5, the following information shall be supplied by the manufacturer to the mooring chain or accessory manufacturer and the results included in the chain documentation:
  1. Each heat shall be examined for non-metallic inclusions according to ISO 4967 or equivalent. The level of inclusions shall be quantified and assessed to be sure inclusion levels are acceptable for the final product.
  2. A sample from each heat shall be macro etched according to ASTM E381 or equivalent to be sure there is no injurious segregation or porosity.
  3. Jominy hardening ability data according to ASTM A255 or equivalent shall be supplied with each heat.


Ch.2 Sec.1 A
204   The manufacturer shall ensure that effective manufacture and process controls are implemented in production. Where deviation from the controls occurs and this could produce products of inferior quality, the manufacturer shall investigate to determine the cause and establish countermeasures to prevent its recurrence. Investigation reports to this effect shall be made available to the purchaser on request.

Ch.2 Sec.1
A 300   Chemical composition

Ch.2 Sec.1 A
301   Specifications for chemical composition shall be agreed between the manufacturer and purchaser. Steel grades R4, R4S and R5 shall contain a minimum of 0.20% molybdenum.

Ch.2 Sec.1 A
302   The chemical composition of each heat shall be determined on a sample taken preferably during the pouring of the heat and shall comply with the specified limits. When multiple heats are tapped into a common ladle, the ladle analysis shall apply.

Ch.2 Sec.1 A
303   The composition shall be determined after all alloying additions have been made and sufficient time allowed for such an addition to homogenize.

Ch.2 Sec.1 A
304   Elements designated as residual and impurity elements in the individual specifications shall not be intentionally added to the steels. The content of such elements shall be reported.

Ch.2 Sec.1 A
305   Adequate controls shall be in place to prevent accumulation of harmful elements such as tin, antimony and arsenic in the final product.

Ch.2 Sec.1
A 400   Heat treatment

Ch.2 Sec.1 A
401   Materials shall be heat treated for mechanical properties as specified in B to D. Heat treatment shall be carried out in a properly constructed furnace which is efficiently maintained and has adequate means for temperature control and is fitted with recording-type pyrometers. The furnace dimensions shall be such as to allow the whole furnace charge to be uniformly heated to the necessary temperature.

Ch.2 Sec.1 A
402   Sufficient thermocouples shall be connected to the furnace charge where it is composed of forged or cast components. Thermocouples should be connected by capacitor discharge welding.

Ch.2 Sec.1 A
403   Records shall identify the furnace used, furnace charge, date, temperature and time at temperature.

Ch.2 Sec.1 A
404   The manufacturer shall ensure that the specified heat treatment is adhered to. Where deviation from the specified heat treatment occurs, the manufacturer shall ensure that affected products are tested or submitted to reheat treatment and that an investigation is carried out according to A204.

Ch.2 Sec.1
A 500   Mechanical testing

Ch.2 Sec.1 A
501   Products shall be grouped in test units and sampled for mechanical testing as detailed in B to D. Test material from which test pieces are prepared shall be of equivalent cross section and be fully representative of the sample product and, where appropriate, shall not be cut, or partially cut from the sample product leaving a ligament, until heat treatment has been completed. Test material and test pieces shall not be separately heat treated in any way.

Ch.2 Sec.1 A
502   Test material and test pieces shall be marked to identify them with the products represented.

Ch.2 Sec.1 A
503   For each test unit, one tensile and three Charpy V-notch test pieces shall be taken. Rolled steel bars and steel forgings shall be tested in the longitudinal direction. The longitudinal axis of test pieces shall be located one-third of the radius or, in the case of non-cylindrical sections, one-sixth of the diagonal from the outer surface.

Ch.2 Sec.1 A
504   The preparation of test pieces and the procedures used for mechanical testing shall comply with the relevant requirements of DNV-OS-B101.

Ch.2 Sec.1 A
505   The materials shall comply with the mechanical properties specified in Table E1.

Ch.2 Sec.1 A
506   If the results from tensile testing do not meet the specified requirements, two further tensile tests may be made from the same sample. If both of these additional tests are satisfactory, the test unit may be accepted.

Ch.2 Sec.1 A
507   If the results from a set of three impact test pieces do not meet the specified requirements, three additional test pieces from the same sample may be tested and the results added to those previously obtained to form a new average. If this new average complies with the requirements and if not more than two individual results are lower than the required average and, of these, not more than one result is below 70% of the specified average value, the test unit may be accepted.

Ch.2 Sec.1 A
508   Where forgings or castings and the associated test material are submitted to re-heat treatment, they may not be re-austenitised more than twice. All the tests previously performed shall be repeated after re-heat treatment and the results must meet the specified requirements.

Ch.2 Sec.1
A 600   Inspection

Ch.2 Sec.1 A
601   Materials are subject to visual inspection, non-destructive testing (NDT) and measurements of dimensions as detailed in B to D. The manufacturers shall prepare written procedures for NDT. NDT personnel shall be qualified and certified according to ISO 9712, EN 473, SNT-TC-1A or equivalent. NDT operators shall be qualified to at least level I.

Ch.2 Sec.1 A
602   NDT shall be performed in accordance with the general practice of recognised standards, e.g.:

Magnetic particle testing (MT) of forgings:
—EN 10228-1, ASTM A275, using wet continuous magnetisation technique

Ultrasonic testing (UT) of forgings:
—EN 10228-3, ASTM A388

Magnetic particle testing (MT) of castings:
—ASTM E709, using wet continuous magnetisation technique

Ultrasonic testing (UT) of castings:
—ASTM A609


Ch.2 Sec.1 A
603   MT of forged or cast accessories shall be carried out after proof load testing. Where a forging or casting is delivered in an intermediate condition for subsequent processing and final MT by the purchaser, the manufacturer should perform suitable intermediate inspections taking into consideration the quality level required in finished condition. In such cases the extent of testing and acceptance criteria shall be agreed between manufacturer and purchaser. See also C600, D600, and Sec.2 C.

Ch.2 Sec.1 A
604   UT of forgings or castings shall be carried out at an appropriate stage after the final heat treatment for mechanical properties, e.g. after proof load testing of finished accessories.

Ch.2 Sec.1
A 700   Repair

Ch.2 Sec.1 A
701   Surface defects may be removed by grinding as detailed in B to D. The resulting grooves shall have a bottom radius of approximately three times the depth and shall be blended into the surrounding surface to avoid any sharp contours. Complete elimination of the defective material shall be verified by suitable NDT.

Ch.2 Sec.1 A
702   Except as provided for steel castings, repair by welding is not permitted.

Ch.2 Sec.1
A 800   Identification

Ch.2 Sec.1 A
801   Each bar, forging, or casting shall be suitably identified with at least the following:
  1. identification number, heat number or other marking that will enable the history of the item to be traced,
  2. steel grade designation.

Ch.2 Sec.1
A 900   Records

Ch.2 Sec.1 A
901   The manufacturer shall maintain traceable records of the following and present them to the purchaser on request:
  1. steelmaking process and chemical composition
  2. heat treatment
  3. mechanical testing
  4. inspection
  5. repair.
Sec.1: Materials [Table of Contents] B: Rolled Steel Bars