Section 2 Castings for ship and other structural applications

2.1.1 The requirements are for carbon, carbon-manganese and alloy steel castings, intended for ship for worldwide service and other structural applications. The requirements also consider grades that are intended for fabrication by welding, as well as grades not intended for welding.

2.1.2 Provision is made for two quality grades, Normal and Special.

2.1.3 Where it is proposed to use carbon-manganese steels of higher specified minimum tensile strength than required by Ch 4, 2.4 Mechanical tests and properties 2.4.3, or alloy steels, particulars of the chemical composition, mechanical properties and heat treatment are to be submitted for approval.

2.2.1 The chemical composition of ladle samples is to comply with Table 4.2.1 Chemical composition of ladle samples for carbon and carbon-manganese hull steel castings and Table 4.2.2 Chemical composition of ladle samples for alloy hull steel castings .

2.2.2 For the Special grade, the product of the aluminium and nitrogen contents is to comply with the following formula:

2.2.3 For the Special grade, a check chemical analysis on the product or a test bar is mandatory. The check analysis on the product or test bar is to comply with the requirements of Table 4.2.3 Mechanical properties for hull steel castings intended for welding and Table 4.2.4 Mechanical properties for hull steel castings not intended for welding.

2.3.1 Castings are to be supplied:

1. fully annealed; or

2. normalised; or

3. normalised and tempered at a temperature of not less than 550°C; or

4. quenched and tempered at a temperature of not less than 550°C.

2.3.2 For larger castings where a coarser microstructure may be present in heavier thickness, a double austenising heat treatment may be required to ensure adequate grain refinement. A coarse microstructure will be indicated by an increased attenuation of approximately 30 dB/m at 2 MHz during ultrasonic examination.

2.3.3 Following the attachment of handling brackets, all castings are to be subject to post weld heat treatment at a temperature of not less than 550°C before delivery.

2.4.1 At least one tensile test is to be made on material representing each casting or batch of castings.

2.4.2 Where the casting is of complex design, or where the finished mass exceeds 10 tonnes, two cast on test samples are to be provided from the heaviest section, located as far as practicable from each other. Where large castings are made from two or more casts which are not mixed in a ladle prior to pouring, two or more test samples are required corresponding to the number of casts involved. These are to be integrally cast at locations as widely separated as possible.

2.4.3 The results of these tensile tests are to comply with the requirements provided in Table 4.2.3 Mechanical properties for hull steel castings intended for welding and Table 4.2.4 Mechanical properties for hull steel castings not intended for welding.

Table 4.2.3 Mechanical properties for hull steel castings intended for welding

Steel type	Specified minimum tensile strength (N/mm2)	Yield stress (N/mm2) min.	Elongation on 5, 65 min.	Reduction of area (%) min.	Charpy V-notch impact test (See Note)
					Test temperature (°C)	Minimum average energy (J)
C, C-Mn	400-550 440-590 480-630 520-670 560-710 600-750	200 220 240 260 300 320	25 22 20 18 15 13	40 30 27 25 20 20	0	27
Alloy	550-700	355	18	30
	600-750	400	16	30
	650-800	450	14	30
	700-850	540	12	28
Note: Special consideration may be given to alternative requirements for Charpy V-notch impact test, depending on design and application, and subject to agreement by LR.

Table 4.2.4 Mechanical properties for hull steel castings not intended for welding

Steel type	Specified minimum tensile strength (N/mm2)	Yield stress (N/mm2) min.	Elongation on 5, 65 min.	Reduction of area (%) min.	Charpy V-notch impact test (See Note 1)
					Test temperature (°C)	Minimum average energy (J)
C, C-Mn	400-550 440-590 480-630 520-670 560-710 600-750	200 220 240 260 300 320	25 22 20 18 15 13	40 30 27 25 20 20	AT (See Note 2)	27
Alloy	550-700	340	16	35
	600-750	400	16	35
	650-800	450	14	32
	700-850	540	12	28
Note 1. Special consideration may be given to alternative requirements for Charpy V-notch impact test, depending on design and application, and subject to agreement by LR. Note 2. AT refers to Ambient Temperature (i.e. 23°C±5°C), which is specified in ISO 148-1.

2.5.1 Castings used in ship construction for the sternframe, rudder and propeller shaft supports are to be examined by ultrasonic and magnetic particle methods in accordance with Ch 4, 1.7 Visual and surface Non-Destructive Examination. The type and extent of Non-Destructive Examination of castings for other structural applications are to be specially agreed by the Surveyor.

2.5.2 The extent and methods of Non-Destructive Examination to be applied to typical hull steel castings are shown in Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings to Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings in addition to the areas specified in Ch 4, 1.7 Visual and surface Non-Destructive Examination 1.7.9 and Ch 4, 1.8 Volumetric Non-Destructive Examination 1.8.1.

Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings

Figure 4.2.2 Extent of non-destructive evaluation for rudder stock castings

Figure 4.2.3 Extent of non-destructive evaluation for stern boss castings

Figure 4.2.4 Extent of non-destructive evaluation for rudder hanging castings

Figure 4.2.5 Extent of non-destructive evaluation for rudder (upper part) castings

Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings

2.5.3 Acceptance levels for visual inspection are to be taken as follows:

1. No cracks, crack-like indications, hot tears or cold shuts are permitted.

2. Castings are to be free of other injurious indications to the satisfaction of the Surveyor.

3. Thickness of the remains of sprues or risers should be within casting dimensional tolerance.

4. Additional magnetic particle, liquid penetrant or ultrasonic testing may be required for a more detailed evaluation of surface irregularities at the request of the Surveyor. These examinations are in addition to those required by Ch 4, 2.6 Acceptance levels for Non-Destructive Examination of castings.

2.6.1 The following definitions apply to indications associated with magnetic particle and liquid penetrant testing:

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

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

3. Aligned indication. Three or more indications in a line, separated by 2 mm or less edge-to-edge, which results in a unique indication defined as follows:

   • 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 contrast 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 contrast 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.

2.6.2 For the purpose of evaluating indications, the surface is to be divided into reference band length of 150 mm for Level MT1/PT1 and into reference areas of 22500 mm² for Level MT2/PT2. The band length and/or area is to be taken in the most unfavourable location relative to the indications being evaluated.

2.6.3 The following quality levels recommended for magnetic particle testing (MT) and/or liquid penetrant testing (PT) are:

1. Level MT1/PT1 – fabrication weld preparation areas.

2. Level MT2/PT2 – other locations indicated on Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings to Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings.

The allowable number and sizes of indications in the reference area are shown in the acceptance criteria detailed in Table 4.2.5 Acceptance criteria for surface inspection evaluation. Cracks, cold shuts and hot tears are not acceptable.

2.6.4 Acceptance criteria for ultrasonic testing are shown in Table 4.2.6 Ultrasonic Acceptance Criteria for steel castings – Using DGS or DAC system as UT1 and UT2. Discontinuities within the examined zones interpreted to be cracks, cold shuts or hot tears are not acceptable.

2.6.5 Level UT1 is applicable to the following:

1. Fabrication weld preparations for a distance of 50 mm.

2. 50 mm depth from the final machined surface including boltholes.

3. Fillet radii to a depth of 50 mm and within a distance of 50 mm from the radius end.

4. Castings subject to cyclic bending stresses, e.g. rudder horn, rudder castings and rudder stocks, the outer one third of thickness in the zones shown in Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings to Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings.

2.6.6 Level UT2 is applicable to the following:

1. For locations which are not specified in Ch 4, 2.6 Acceptance levels for Non-Destructive Examination of castings 2.6.5, nominated for ultrasonic testing in Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings to Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings or on the inspection plan.

2. Positions outside locations nominated for level UT1 examination where feeders and gates have been removed.

3. Castings subject to cyclic bending stresses, at the central one third of thickness in the zones shown in Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings to Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings.

2.6.7 Ultrasonic acceptance criteria for casting areas not nominated in Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings to Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings will be subject to special consideration based on the anticipated stress levels and the type, size and position of the discontinuity.

2.6.8 Parts which are welded are to be examined by the same method as at the initial inspection as well as by additional methods as required by the Surveyor.

2.6.9 The maximum number of indications to be recorded and the maximum length of indications permissible for quality Level UT2 apply to normal probes.

2.6.10 For quality Level UT2, any discontinuity producing a signal amplitude in excess of the 15 mm DAC curve is to be regarded as unacceptable.

2.6.11 Any signal between 12 mm FBH + 15 mm FBH curve is to be evaluated for length of defect.

2.6.12 For near surface testing, to an approximate depth of 25 mm, a twin crystal 0° - normal beam - probe should be used, plus a single crystal 0° probe, beyond a depth of 25 mm, for the remaining volume.

2.6.13 Ultrasonic acceptance criteria for other casting areas not specified in Figure 4.2.1 Extent of non-destructive evaluation for stern frame castings to Figure 4.2.6 Extent of non-destructive evaluation for rudder (lower part) castings is to be subject to special consideration based on the anticipated stress levels during service and the type, size and position of the discontinuity.

2.6.14 DGS and DAC methods may be used for determining sensitivity. The DAC method for normal beam probes may be based on a 6 mm diameter reflector or FBH. A DAC curve is to be produced using reference blocks containing 6 mm FBH reflectors over a range representative of the inspection thickness, after adjustment for transfer and attenuation losses.

2.6.15 For quality Level UT1, any discontinuity producing a signal amplitude in excess of the 6 mm DAC curve is unacceptable.

2.6.16 For quality Level UT2, the sensitivity may be based on actual size FBH (of 12 mm and 15 mm) or based on equivalent 6 mm FBH, and the sensitivity adjusted to obtain equivalent amplitudes, as described in Ch 4, 2.6 Acceptance levels for Non-Destructive Examination of castings 2.6.17.

2.6.17 When setting sensitivity using 6 mm FBH, adjustment of signal amplitudes - measured in dB above 6 mm DAC - can be determined for 12 mm and 15 mm FBH reflectors, i.e. DAC + 12 dB and DAC + 16 dB, plus any compensation for transfer and attenuation losses, as illustrated in Figure 4.2.7 DAC curve produced from 6 mm FBH reflector and DAC curves adjusted to represent equivalent 12 mm and 15 mm FBH reflectors. The increase in dB to the indicated levels represents the equivalent FBH sizes (for 12 mm and 15 mm), and their respective corresponding ultrasonic response amplitudes.

Figure 4.2.7 DAC curve produced from 6 mm FBH reflector and DAC curves adjusted to represent equivalent 12 mm and 15 mm FBH reflectors

• The bottom curve (DAC) represents a sensitivity based on 6 mm FBH, and the two additional curves (DAC + 12 dB and DAC + 16 dB) above this represent the equivalent sensitivities converted for larger FBHs (12 mm and 15 mm).
• When scanning using these curves and applying Table 4.2.6 Ultrasonic Acceptance Criteria for steel castings – Using DGS or DAC system for UT2, any indication below DAC + 12 dB is to be disregarded, and any indication above DAC + 16 dB is to be rejected.

Any indication between these two curves is to be evaluated according to its size, as per Table 4.2.6 Ultrasonic Acceptance Criteria for steel castings – Using DGS or DAC system.