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C: Steel Forgings [Table of Contents] E: Materials for Studs

DNV-OS-E302 Offshore Mooring Chain

[-] Ch.2: Technical Provisions
[-] Sec.1: Materials
[-] D: Steel Castings

Ch.2 Sec.1
D. Steel Castings

Ch.2 Sec.1
D 100   Scope

Ch.2 Sec.1 D
101   These requirements are supplementary to A and apply to steel castings to be used in the manufacture of chain accessories. Additional requirements for the finished accessories are given in Sec.2 C.

Ch.2 Sec.1
D 200   Manufacture

Ch.2 Sec.1 D
201   Castings shall be manufactured according to drawings showing the positions of gates, risers and chills (if used).

Ch.2 Sec.1 D
202   Where flame cutting, scarfing or arc-air gouging to remove surplus metal is undertaken, the affected areas shall be either machined or ground smooth.

Ch.2 Sec.1
D 300   Chemical composition

Ch.2 Sec.1 D
301   The chemical composition shall comply with the agreed specification.

Ch.2 Sec.1
D 400   Heat treatment

Ch.2 Sec.1 D
401   Cast accessories in grade R3 and R3S shall be supplied in the normalised, normalised and tempered, or quenched and tempered condition. Grade R4, R4S and R5 shall be supplied in the quenched and tempered condition. Quenched and tempered accessories with diameter over 120 mm shall receive an annealing or normalising heat treatment prior to quenching and tempering.

Ch.2 Sec.1 D
402   For grade R4, R4S and R5, tempering temperatures shall not be less than 590°C and cooling after tempering shall be in water.

Ch.2 Sec.1
D 500   Mechanical testing

Ch.2 Sec.1 D
501   Cast accessories shall be mechanically tested as given in Sec.2 C.

Ch.2 Sec.1
D 600   Inspection

Ch.2 Sec.1 D
601   All castings shall be visually inspected on accessible surfaces. Where applicable, this is to include the inspection of internal surfaces and bores. The surfaces shall be adequately prepared for inspection.

Ch.2 Sec.1 D
602   Castings shall be free from adhering sand, scale, cracks, hot tears or other imperfections which, due to their nature, degree or extent, will interfere with the use of the castings.

Ch.2 Sec.1 D
603   All finished accessories are subject to MT, see A600 and Sec.2 C.

Ch.2 Sec.1 D
604   Ultrasonic testing shall be carried out on all castings after the final heat treatment when the surfaces have been brought to a condition suitable for UT. Both radial and axial scanning shall be used when appropriate for the shape and dimensions of the casting being tested. Unless otherwise agreed with the purchaser the entire volume of the castings shall be tested.

Ch.2 Sec.1 D
605   For calibration, reference blocks shall be made from steel that is similar in chemistry and processing history to the production castings. The distance amplitude curve (DAC) shall be based on 3 mm flat bottom hole for testing to a depth of 25 mm below the surface and 6 mm flat bottom hole for testing the remaining volume. No indications equal to or larger than the reference DAC are accepted.

Ch.2 Sec.1
D 700   Repair

Ch.2 Sec.1 D
701   Defects on non-machined surfaces may be removed by grinding to a depth of 5% of the nominal diameter. Grinding is not permitted on machined surfaces, except for slight inspection grinding on plane surfaces in order to investigate spurious indications.

Ch.2 Sec.1 D
702   Where the repair entails removal of more than 5% of the diameter or thickness, the defective area shall be repaired by welding. The excavations shall be suitably shaped to allow good access for welding. The resulting grooves shall be subsequently ground smooth and complete elimination of the defective material shall be verified by NDT.

Ch.2 Sec.1 D
703   Weld repairs are classified as major or minor. A weld repair is considered major when the depth of the groove prepared for welding exceeds 25% of the diameter or 25 mm, whichever is smaller. All other weld repairs are considered minor.

Ch.2 Sec.1 D
704   Major weld repairs require the approval of the purchaser before the repair is commenced. Proposals for major repairs shall be accompanied by sketches or photographs showing the extent and positions of the repairs. A grain refining heat treatment shall be given to the whole casting prior to major repairs.

Ch.2 Sec.1 D
705   Minor weld repairs must be recorded on sketches or photographs showing the extent and positions of the repairs.

Ch.2 Sec.1 D
706   All weld repairs shall be done by qualified welders using qualified procedures. Welders shall be qualified according to EN 287, ISO 9606, ASME IX, ASTM A488 or equivalent. Procedures shall be qualified according to EN 288, ASME IX, ASTM A488 or equivalent with the following additional requirements: Charpy V-notch impact tests with notch locations in weld metal, fusion line and heat affected zone + 2 mm and + 5 mm from fusion line, respectively. Test results shall meet the requirements specified for the parent metal.

Ch.2 Sec.1 D
707   The welding consumables used shall be of a suitable composition giving a weld deposit with mechanical properties similar to those of the parent castings. Low hydrogen consumables shall be used. Welding consumables shall be stored and handled so as to maintain the hydrogen classification and in accordance with the consumable manufacturer's recommendations.

Ch.2 Sec.1 D
708   When repair welding is done after the casting has been heat treated for mechanical properties, the repaired casting shall be given a furnace stress relieving or tempering heat treatment as detailed in the qualified procedure.

Ch.2 Sec.1 D
709   On completion of heat treatment the weld repairs and adjacent material shall be ground smooth. All weld repairs are subject to NDT as required by 600.
C: Steel Forgings [Table of Contents] E: Materials for Studs