Section 1 General requirements

1.1.1 This Section gives the general requirements for steel forgings intended for use in the construction of ships, other marine structures, machinery, boilers, pressure vessels and piping systems. These requirements are also applicable to rolled slabs and billets used as a substitute for forgings and to rolled bars used for the manufacture (by machining operations only) of shafts, bolts, studs and other components of similar shape.

1.1.2 When required by the relevant Rules dealing with design and construction, forgings are to be manufactured and tested in accordance with Ch 1 General Requirements and Ch 2 Testing Procedures for Metallic Materials, together with the general requirements given in this Section and the appropriate specific requirements given in Sections Ch 5, 2 Forgings for ship and other structural applications to Ch 5, 9 Stainless steel forgings.

1.1.3 As an alternative to Ch 5, 1.1 Scope 1.1.2, steel forgings which comply with National or proprietary specifications may be accepted provided that these specifications give reasonable equivalence to the requirements of this Chapter or alternatively are approved for a specific application. Generally, survey and certification are to be carried out in accordance with the requirements of Ch 1 General Requirements.

1.1.4 Where small forgings are produced in large quantities, or where forgings of the same type are produced in regular quantities, alternative survey procedures in accordance with Ch 1, 2.4 Materials Quality Scheme may be adopted.

1.2.1 Forgings are to be made at works which have been approved by Clasifications Register (hereinafter referred to as LR). The steel used is to be manufactured in accordance with the requirements of the Rules for the Manufacture, Testing and Certification of Materials, Ch 3, 1.4 Manufacture. Where the steel is produced at a separate works to the forging, the steel manufacturer is also to be approved by LR.

1.2.2 When forgings are made directly from ingots, or from blooms or billets forged from ingots, the ingots are to be cast in chill moulds with the larger cross-section uppermost and with efficient feeder heads.

1.2.3 Adequate top and bottom discards are to be made to ensure freedom from piping and harmful segregations in the finished forgings.

1.2.4 The forgings are to be gradually and uniformly hot worked and are to be formed as closely as possible to the finished shape and size. The plastic deformation is to be such as to ensure soundness, uniformity of structure and satisfactory mechanical properties after heat treatment.

1.2.5 For certain components, such as crankshafts, where grain flow is required in the most favourable direction having regard to the mode of stressing in service, the proposed method of manufacture may require special approval by LR. In such cases, tests may be required to demonstrate that a satisfactory structure and grain flow are obtained.

1.2.6 The reduction ratio (reduction of area expressed as a ratio) is to be calculated with reference to the average cross-sectional area of the ingot or continuously cast material, where appropriate. Where an ingot is initially upset, this reference area may be taken as the average cross-sectional area after this operation.

1.2.7 For components forged directly from ingots or from forged blooms or billets, and in which the fibre deformation is mainly longitudinal, the reduction ratio is not to be less than 3:1.

1.2.8 For forgings made from rolled billets, or where fibre deformation has taken place in more than one direction, the reduction ratio is not to be less than 4:1.

1.2.9 Where rolled bars are used as a substitute for forgings and the requirements of Ch 5, 1.2 Manufacture 1.2.2 are not complied with, the reduction ratio is to be not less than 6:1 unless otherwise accepted by the LR Surveyor.

1.2.10 Where the length of any section of a shaft forging is less than its diameter (e.g. a collar), the reduction ratio is to be not less than half that given in Ch 5, 1.2 Manufacture 1.2.7, Ch 5, 1.2 Manufacture 1.2.8 or Ch 5, 1.2 Manufacture 1.2.9 respectively.

1.2.11 Disc type forgings, such as gear wheels, are to be made by upsetting, and the thickness of any part of the disc is to be not more than one-half of the length of the billet from which it was formed, provided that this billet has received an initial forging reduction of not less than 1,5:1. Where the piece used has been cut directly from an ingot, or where the billet has received an initial reduction of less than 1,5:1, the thickness of any part of the disc is to be not more than one-third of the length of the original piece.

1.2.12 Rings and other types of hollow forgings are to be made from pieces cut from ingots or billets and which have been suitably punched, bored or trepanned prior to expanding or hollow forging. Alternatively, pieces from hollow cast ingots may be used. The wall thickness of the forging is to be not more than one-half of the thickness of the prepared hollow piece from which it was formed. Where this is not practicable, the forging procedure is to be such as to ensure that adequate work is given to the piece prior to punching, etc. This may be either longitudinal or upset working of not less than 2:1.

1.2.13 The shaping of forgings or rolled slabs and billets by flame cutting, scarfing or arc-air gouging is to be undertaken in accordance with recognised good practice and, unless otherwise approved, is to be carried out before the final heat treatment. Preheating is to be employed where necessitated by the composition and/or thickness of the steel. For certain components, subsequent machining of all flame cut surfaces may be required, see Ch 5, 4.2 Manufacture 4.2.4.

1.2.14 Where two or more forgings are joined by welding to form a composite component, details of the proposed welding procedure are to be submitted for approval. Welding approval procedure tests are to be required in accordance with Rules for the Manufacture, Testing and Certification of Materials, Ch 12 Welding Qualifications.

1.2.15 It is recognised that not every forged component type that may be subject to classification is included in this Chapter. In such cases where the particular component or type is not included, appropriate National/International Standards may be applied, to determine the appropriate testing regime and defect acceptance criteria.

1.3.1 All forgings are to be free from surface or internal defects which would be prejudicial to their proper application in service.

1.4.1 All forgings are to be made from killed steels, and the chemical composition of ladle samples is to comply with the requirements detailed in subsequent Sections in this Chapter. Where general overall limits are specified, the chemical composition selected is to be appropriate for the type of steel, dimensions and required mechanical properties of the forgings being manufactured.

1.4.2 Except where otherwise specified, suitable grain refining elements such as aluminium, niobium or vanadium may be used at the discretion of the manufacturer. The content of such elements is to be reported in the ladle analysis.

1.4.3 For alloy steel forgings, the chemical composition of ladle samples is to comply with the requirements of Table 5.2.1 Chemical composition limits for hull steel forgings and Table 5.3.1 Chemical composition limits for machinery steel forgings.Chemical compositions contained in alternative standards will be specially considered for their intended application.

1.5.1 At an appropriate stage of manufacture, after completion of all hot working operations, forgings are to be suitably heat treated to refine the grain structure and to obtain the required mechanical properties. Acceptable heat treatment procedures are to be such as to avoid the formation of hair-line cracks and are detailed in Sections Ch 5, 2 Forgings for ship and other structural applications to Ch 5, 9 Stainless steel forgings.

1.5.2 Heat treatment is to be carried out in a properly constructed furnace which is efficiently maintained and has adequate means of temperature control. The furnace dimensions are to be such as to allow all the steel forgings to be uniformly heated to the necessary temperature. In the case of very large forgings, alternative methods of heat treatment will be specially considered. Sufficient thermocouples are to be connected to the steel forging(s) in the furnace to show that the temperature is adequately uniform and the temperatures are to be recorded throughout the heat treatment. Copies of these records are to be presented to the Surveyor together with a sketch showing the positions at which the temperature measurements were carried out. The records are to identify the furnace that was used and give details of the steel-making heat, the heat treatment temperature, time at temperature and the date. The Surveyor is to examine the charts and confirm the details on the certificate.

1.5.3 As an alternative procedure to the connection of thermocouples as required by Ch 5, 1.5 Heat treatment 1.5.2, temperature uniformity surveys of the heat treatment furnace may be accepted subject to approval by LR, Materials and NDE department. An initial temperature uniformity survey in the furnace fully loaded condition is required to be carried out in accordance with recognised standards (e.g. ASTM A991/A991M). Regular temperature uniformity surveys are then subsequently required at a frequency of at least once per year.

1.5.4 Where forgings are to be quenched and tempered and cannot be hot worked close to size and shape, they are to be suitably rough machined or flame cut prior to being subjected to this treatment.

1.5.5 If for any reason a forging is subsequently heated for further hot working, the forging is to be reheat treated.

1.5.6 If any straightening operation is performed after the final heat treatment, consideration should be given to a subsequent stress relieving heat treatment in order to avoid the possibility of harmful residual stresses. The manufacturer shall have strict control of the stress relieving heat treatment temperature in order to avoid any detrimental effects on the final heat treatment and the resultant microstructure and mechanical properties of the forging.

1.5.7 Where it is intended to surface harden forgings, full details of the proposed procedure and specification are to be submitted for approval. For the purposes of this approval, the manufacturer will be required to demonstrate by tests that the proposed procedure gives a uniform surface layer of the required hardness and depth and that it does not impair the soundness and properties of the steel.

1.5.8 Where induction hardening or nitriding is to be carried out after machining, forgings are to be heat treated at an appropriate stage to a condition suitable for this subsequent surface hardening.

1.5.9 Where carburising is to be carried out after machining, forgings are to be heat treated at an appropriate stage (generally either by full annealing or by normalising and tempering) to a condition suitable for subsequent machining and carburising.

1.5.10 The forge is to maintain records of heat treatment identifying the furnace used, furnace charge, thermocouple location, date, temperature and time at temperature. The records are to be presented to the Surveyor on request.

1.6.1 Test material, sufficient for the required tests and for possible re-test purposes, is to be provided with a cross-sectional area of not less than that part of the forging which it represents. This test material is to be integral with each forging, except in the case of small forgings which are batch tested, see Ch 5, 1.6 Test material 1.6.4.

1.6.2 Where a forging is subsequently divided into a number of components, all of which are heat treated together in the same furnace, for test purposes this may be regarded as one forging and the number of tests required is to be related to the total length and mass of the original multiple forging, see Ch 5, 2.4 Mechanical tests 2.4.2.

1.6.3 Except for components which are to be carburised, test material is not to be cut from a forging until the heat treatment detailed in Ch 5, 2 Forgings for ship and other structural applications to Ch 5, 9 Stainless steel forgings has been completed. The testing procedure for components which are to be carburised is to be in accordance with the details given in Ch 5, 5 Forgings for gearing.

1.6.5 When required by the conditions of approval for surface hardened forgings (see Ch 5, 1.5 Heat treatment 1.5.7) additional test samples are to be processed at the same time as the forgings which they represent. These test samples are subsequently to be sectioned in order to determine the hardness, shape and depth of the locally hardened zone and which of them are to comply with the requirements of the approved specification.

1.7.1 Specimens for mechanical tests are to be prepared as required by Ch 5, 2 Forgings for ship and other structural applications to Ch 5, 9 Stainless steel forgings.

1.7.2 Test specimens are normally to be cut with their axes either mainly parallel (longitudinal test) or mainly tangential (tangential test) to the principal axial direction of each product.

1.7.3 The test specimens shall be positioned as follows:

1. For forgings with a thickness, t, or diameter D up to a maximum 50 mm, the longitudinal axis of the test specimen is to be located at a distance of t/2 or D/2 below the heat-treated surfaces.

2. For forgings with a thickness, t, or diameter D greater than 50 mm, the longitudinal axis of the test specimen is to be located at a distance of t/4 or D/4 (mid-radius) or 80 mm, whichever is less, below any heat-treated surface. Test specimen is to be located with its longitudinal axis at a distance from any heat-treated surface as shown in Figure 5.1.1 Position of the test specimen.

3. For ring and disc forgings (note that the test specimen locations for these shaped forgings may be different to elongated or free from forgings), tangential samples shall be taken at t/2 for thickness ≤ 25 mm and 12,5 mm below the surface for thickness greater than 25 mm, in both the vertical and horizontal directions as shown in Figure 5.1.1 Position of the test specimen.

Where achievable, for thickness greater than 25 mm, no part of the test material shall be closer than 12,5 mm to any heat-treated surface, as shown in Figure 5.1.1 Position of the test specimen.

Figure 5.1.1 Position of the test specimen

1.7.4 Where the manufacturer can demonstrate that a proposed testing location or orientation is more representative of the required mechanical properties of a component, this may be agreed with LR. In such cases, the heat treatment process, a proposed testing location or orientation, and technical justification, shall be submitted to LR for approval.

1.7.5 Tensile test specimens are to be machined to the dimensions detailed in Ch 2 Testing Procedures for Metallic Materials. Where this is precluded by the dimensions of the forging, the test specimen is to be of the largest practicable cross-sectional area.

1.7.6 Impact test specimens are to be prepared in accordance with the requirements of Ch 2 Testing Procedures for Metallic Materials.

1.7.7 The procedures used for the tensile and impact tests are to be in accordance with the requirements of Ch 2 Testing Procedures for Metallic Materials.

1.7.8 Hardness tests, preferably of the Brinell type, are to be carried out when specified in subsequent Sections in this Chapter.

1.8.1 All forgings should be subjected to a 100 per cent visual examination of all accessible surfaces by the manufacturer and the results of these examinations made available to the Surveyor. Where applicable, this visual examination is to include the examination of internal surfaces and bores. Unless otherwise agreed, the verification of dimensions is the responsibility of the manufacturer.

1.8.2 Forgings are to be examined in the condition for final delivery. Surfaces are to be clean and free from dirt, grease, paint, etc. Black forgings are to be suitably descaled by either shotblasting or flame descaling methods.

1.8.3 All forgings are to be free of cracks, crack-like indications, laps, seams, folds, or other injurious indications. At the request of the Surveyor, additional magnetic particle, dye penetrant and ultrasonic testing may be required for a more detailed evaluation of surface irregularities.

1.8.5 Magnetic particle and liquid penetrant testing is to be carried out when the forgings are in the finished machined condition, see also Ch 1, 2.3 Materials Survey Scheme 2.3.5. For magnetic particle testing, attention is to be paid to the contact between the forging and the clamping devices of stationary magnetisation benches in order to avoid local overheating or burning damage on its surface. Prods are not permitted on finished machined items. The surface inspection is to be carried out before the shrink fitting, where applicable. Unless otherwise agreed, these tests are to be carried out in the presence of the Surveyor. Other surface inspection methods, e.g. eddy current testing, may be required by LR as a supplementary method, e.g. for confirming the presence of indications, or for detecting the presence of undocumented weld repairs.

1.8.6 The following definitions apply to indications associated with magnetic particle and liquid penetrant inspection:

1. Linear indication. An indication with a largest dimension, l, three or more times its smallest dimension, w (i.e. l ≥ 3w).

2. Nonlinear indication. An indication with a largest dimension less than three times its smallest dimension (i.e. l < 3w).

3. Aligned indication.

   • Non-linear indications form an alignment when the distance between indications is less than 2 mm and at least three indications are aligned. An alignment of indications is considered to be a unique indication and its length is equal to the overall length of the alignment.
   • Linear indications form an alignment when the distance between two indications is smaller than the length of the longest indication.

4. Open indication. An indication visible after removal of the magnetic particles or that can be detected by the use of liquid penetrant testing.

5. Non-open indication. An indication that is not visually detectable after removal of the magnetic particles or that cannot be detected by the use of liquid penetrant testing.

6. Relevant indication. An indication that is caused by a condition or type of discontinuity that requires evaluation. Only indications which have any dimension greater than 1,5 mm are to be considered relevant for the categorisation of indications.

1.8.7 Acceptance standards for defects found by visual or non destructive examinations are to be in accordance with any specific requirements of the approved plan, and with equivalence to any additional requirements of this Chapter. In all cases they are to be to the satisfaction of the Surveyor.

1.8.8 Where required, ultrasonic examination is to be carried out after the forgings have been machined to a condition suitable for this type of examination and after the final heat treatment, but prior to the drilling of oil bores, prior to surface hardening and the machining of bolt threads. Both radial and axial scanning are to be carried out where appropriate for the shape and the dimensions of the forgings being examined. Scanning is to take into account near surface examination. Unless otherwise agreed, examinations are to be carried out by the manufacturer, although Surveyors may request to be present in order to verify that the examination is being carried out in accordance with the agreed procedure.

1.8.9 If the forging is supplied in the black condition for machining at a separate works, the manufacturer is to ensure that a suitable ultrasonic examination is carried out to verify the internal quality of the forging.

1.8.10 In the circumstance detailed in either Ch 5, 1.8 Visual and Non-Destructive Examination 1.8.8 or Ch 5, 1.8 Visual and Non-Destructive Examination 1.8.9, the manufacturer is to provide the Surveyor with a signed report confirming that ultrasonic examination has been carried out and that such inspection has not revealed any significant internal defects.

1.8.11 In the event of any forging proving defective during subsequent machining or testing, it is to be rejected notwithstanding any previous certification.

1.8.12 Fillet radii should be examined using 45°, 60° or 70° probes, primarily to determine the presence of any cracks within the radiused areas, and as an additional scan to confirm any indications that may have been detected with 0° probe(s) within this area.

1.8.13 For fabricated forgings and weld repairs, weld testing is to be carried out to the appropriate standard, and the acceptance determined by reference to Table 13.2.7 Acceptance criteria for ultrasonic and phased array testing.

1.8.14 Construction of DAC curves for straight beam or normal probes are to be performed using reference blocks containing suitably sized Flat Bottom Holes (FBH) spaced over the inspection thickness. Reference blocks are to be manufactured from similar material, with a surface condition similar to that being inspected. Where necessary, allowances are to be made for attenuation losses by performing a transfer correction and adjusting the DAC curve as required. The applied transfer correction (measured in decibels (dB)) is to become the new reference sensitivity, against which indications are evaluated, according to the appropriate table contained in this Chapter, see Ch 5, 3.5 Non-Destructive Examination 3.5.6 and Table 5.4.5 Ultrasonic acceptance criteria for crankshafts: DGS Method – Normal probes.

1.8.15 Distance Gain Size (DGS) diagrams may also be used for normal probes with acceptance criteria and appropriate disc shaped reflector size defined in Ch 5, 3.5 Non-Destructive Examination 3.5.6 and Table 5.4.5 Ultrasonic acceptance criteria for crankshafts: DGS Method – Normal probes.

1.8.16 Where angle probes are used, the reference sensitivity is to be established by using either DAC or DGS methods. DAC sensitivity shall be established from 3 mm side drilled holes and the DGS method shall be based on appropriately sized flat bottom holes. Reference blocks are not required for the DGS method unless it is required to check the accuracy of a particular DGS diagram.

1.8.17 Advanced NDE methods, as described in Ch 1, 5.11 Advanced NDE methods, may be applied to forgings, as appropriate to the material type, thickness, complexity and geometry. Acceptance and rejection criteria levels are to be as per the applicable Section of this Chapter.

1.8.18 Where such standards are used or referenced as a basis for acceptance and rejection criteria, the quality level is to be equivalent to the allowable criteria stated in the appropriate tables within this Chapter. The quality levels would normally be the highest, or most stringent, to provide reasonable equivalence.

1.9.1 Small surface imperfections may be removed by grinding or by chipping and grinding. Complete elimination of these imperfections is to be proved by magnetic particle or dye penetrant examination (as appropriate to the material). At the discretion of the Surveyor, the resulting shallow grooves or depressions can be accepted, provided that they are blended by grinding.

1.9.2 Repairs by welding are not generally permitted, but special consideration will be given to such repairs where they are of a minor nature and in areas of low working stresses. In such cases, full details of the proposed repair and subsequent inspection procedures are to be submitted for review by the Surveyors prior to the commencement of the proposed rectification. A report and/or sketch detailing the extent and location of all repairs, together with details of the post-weld heat treatment and non-destructive examination are to be provided for record purposes and are to be attached to the certificate.

1.9.3 Repair welding is not permitted for forgings subject to torsional fatigue, such as crankshafts and propeller shafts.

1.9.4 Where fabrication welding is involved, see Ch 5, 1.2 Manufacture 1.2.14, any repair of defects is to be carried out in accordance with the approved welding procedure.

1.9.5 The forging manufacturer is to maintain records of repairs and subsequent inspections traceable to each forging. The records are to be presented to the Surveyor on request.

1.9.6 Non-open indications evaluated as segregation are acceptable.

1.10.1 The manufacturer is to adopt a system of identification, as per the requirements of Ch 1, 4.8 Identification of materials, which will enable all finished forgings to be traced to the original cast, forging process and heat treatment batch, and the Surveyor is to be given full facilities to trace the forgings when required.

1.10.2 Forgings are to be clearly marked by the manufacturer in accordance with the requirements of Ch 1 General Requirements. The following details are to be shown on all forgings which have been accepted:

1. Manufacturer’s name or trademark, steel quality, materials grade, identification number, cast number or other marking which will enable the full history of the forging to be traced.

2. LR or Clasifications Register and the abbreviated name of LR's local office.

3. Personal stamp of Surveyor responsible for inspection.

4. Test pressure, where applicable.

5. Date of final inspection.

1.10.3 Modified arrangements for the identification of small forgings manufactured in large numbers, as with closed-die forgings may be agreed with the Surveyor.

1.11.1 A LR certificate is to be issued, see Ch 1, 3.1 General.

1.11.2 The manufacturer is to provide the Surveyor with a written statement giving the following particulars for each forging or batch of forgings which has been accepted:

1. Purchaser's name and order number.

2. Description of forgings and steel quality.

3. Identification number.

4. Steel-making process, cast number and chemical analysis of ladle samples.

5. General details of heat treatment, including temperature and holding times.

6. Results of mechanical tests.

7. Test pressure, where applicable.

8. Results of non-destructive tests, where applicable.

1.11.3 As a minimum, the chemical composition of ladle samples is to include the content of all the elements detailed in the specific requirements.

1.11.4 Where applicable, the manufacturer is also to provide a signed report regarding ultrasonic examination as required by Ch 5, 1.8 Visual and Non-Destructive Examination 1.8.8, a report of magnetic particle inspection and a statement and/or sketch detailing all repairs by welding as required by Ch 5, 1.9 Rectification of defects 1.9.2.

1.11.5 When steel is not produced at the works at which it is forged, a certificate is to be supplied by the steelmaker stating the process of manufacture, cast number and the chemical composition of ladle samples. The works at which the steel was produced is to have been approved by LR, see Ch 5, 1.4 Chemical composition 1.4.3.