Section 5 Castings for propellers
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules for the Manufacture, Testing and Certification of Materials, July 2022 - Chapter 4 Steel Castings - Section 5 Castings for propellers

Section 5 Castings for propellers

Parent topic: Chapter 4 Steel Castings

5.1 Scope

5.1.1 This Section gives the requirements for steel castings for one-piece propellers and separately cast blades and hubs for fixed pitch and controllable pitch propellers (CPP). These include contra-rotating propellers, azipods and azimuth thrusters. The requirements for copper alloy propellers, blades and hubs are given in Ch 9, 1 Castings for propellers.

5.1.2 These castings are to be manufactured and tested in accordance with the appropriate requirements of Ch 1 General Requirements and Ch 2 Testing Procedures for Metallic Materials and Ch 4, 1 General requirements as well as the requirements of this Section.

5.1.3 Full details of the manufacturer's specification are to be submitted for approval. These should include the chemical composition, heat treatment, mechanical properties, microstructure and repair procedures.

5.1.4 Special requirements are given for castings which are intended for ice service in Table 4.5.2 Typical mechanical properties for steel propeller castings.

5.2 Chemical composition

5.2.1 The chemical composition of ladle samples is to comply with the approved specification, see Ch 4, 5.1 Scope 5.1.3.

5.2.2 Typical cast steel propeller alloys are given in Table 4.5.1 Typical chemical composition for steel propeller castings Cast steel whose chemical composition deviates from the typical values of Table 4.5.1 Typical chemical composition for steel propeller castings shall be specially approved by LR.

Table 4.5.1 Typical chemical composition for steel propeller castings

Alloy type C Max. (%) Mn Max. (%) Cr (%) Mo Max. (%) (see Note) Ni (%)
Martensitic
(12Cr 1Ni) 		0,15 2,0 11,5 – 17,0 0,5 Max. 2,0
Martensitic
(13Cr 4Ni) 		0,06 2,0 11,5 – 17,0 1,0 3,5 – 5,0
Martensitic
(16Cr 5Ni) 		0,06 2,0 15,0 – 17,5 1,5 3,5 – 6,0
Austenitic
(19Cr 11Ni) 		0,12 1,6 16,0 – 21,0 4,0 8,0 – 13,0

Note Minimum values are to be in accordance with the agreed specification or recognised National or International Standards.

5.3 Heat treatment

5.3.1 Martensitic stainless steel castings are to be austenitised, quenched and tempered in accordance with the approved specification, see Ch 4, 5.1 Scope 5.1.3.

5.3.2 Austenitic stainless steel castings are to be solution treated in accordance with the approved specification, see Ch 4, 5.1 Scope 5.1.3.

5.4 Mechanical tests

5.4.1 The test material is to be cast integral with the boss of propeller castings, or with the flange of separately cast propeller blades. Alternatively, the test material may be attached on blades in an area between 0,5 and 0,6R, where R is the radius of the propeller.

5.4.2 The test material is not to be removed from the casting until final heat treatment has been carried out. Removal is to be by non-thermal procedures.

5.4.3 At least one tensile test and for the martensitic stainless steel grades one set of three Charpy V-notch impact tests are to be made on material representing each casting. The results are to comply with the requirements of Table 4.5.2 Typical mechanical properties for steel propeller castings or the approved specification.

Table 4.5.2 Typical mechanical properties for steel propeller castings

Alloy type Yield stress or, 0,2% proof stress minimum, N/mm2 Tensile strength minimum N/mm2 Elongation on 5,65 % minimum Reduction of area % minimum Charpy V-notch impact tests J minimum (see Notes 1 and 2)
Martensitic (12Cr 1Ni) 440 590 15 30 20
Martensitic (13Cr 4Ni) 550 750 15 35 30
Martensitic (16Cr 5Ni) 540 760 15 35 30
Austenitic (19Cr 11Ni) 180 (see Note 3) 440 30 40 -

Note 1. When a general service notation Ice Class 1AS, 1A, 1B or 1C is required, the tests are to be made at –10°C.

Note 2. For general service or where the notation Ice Class 1D is required, the tests are to be made at 0°C.

Note 3. R p1,0 value is 205 N/mm2.

5.4.4 As an alternative to Ch 4, 5.4 Mechanical tests 5.4.3, where a number of small propeller castings of about the same size, and less than 1 m in diameter, are made from one cast and heat treated together in the same furnace, a batch testing procedure may be adopted using separately cast test samples of suitable dimensions. At least one set of mechanical tests is to be provided for each multiple of five castings in the batch.

5.4.5 Separately cast test bars may be used subject to prior approval of the Surveyor. Test bars must be cast from the same heat, or heats, and must also be heat treated with castings they represent.

5.5 Quality of castings, inspection, and Non-Destructive Examination

5.5.1 All finished castings are to be 100 per cent visually inspected by the manufacturer. A comprehensive visual examination is to be carried out by the Surveyor.

5.5.2 Castings are to have a workmanlike finish and are to be free from cracks, hot tears, or other imperfections which would be prejudicial to their proper application in service.

5.5.3 Minor casting defects which may still be visible after machining such as small sand and slag inclusions, small cold shuts and scabs are to be suitably removed by mechanical means such as chipping or grinding.

5.5.4 In order to relate the degree of NDE inspection to the criticality of imperfections in propeller blades and to help reduce the risk of failure by fatigue cracking after repair, propeller blades are divided into three severity zones designated A, B and C, as given in Ch 9, 1.8 Inspection and non-destructive examination and Figure 9.1.2 Severity zones in all propeller blades. Proposals by the propeller designer for a modified zone area based on detailed hydrodynamic load and stress analysis may be considered by LR in conjunction with the requirements of the Rules and Regulations for the Classification of Ships, July 2022, Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.7 and relevant sections within the appropriate Rules set.

5.5.5 For all propellers, separately cast blades, and hubs, the surfaces covered by severity Zones A, B and C are to be subjected to penetrant testing, or magnetic particle testing as appropriate to the material type. Testing of Zone A is to be undertaken in the presence of the Surveyor, whilst testing of Zones B and C may be witnessed by the Surveyor upon their request.

5.5.6 If repairs have been made either by grinding or by welding, the repaired areas are additionally to be subjected to liquid testing (or magnetic particle testing, as appropriate) independent of their location and/or severity zone. Weld repairs are, independent of their location, always to be assessed according to Zone A.

5.5.7 The surface to be inspected shall be divided into reference areas of 100 cm2. The indications detected are not, with respect to their size and number, to exceed the values given in Table 4.5.3 Allowable number and size of relevant indications in a reference area of 100 cm2(see Note 1). The area is to be taken in the most unfavourable location relative to the indication being evaluated.

5.5.8 The following definitions apply in relation to the assessment of indications when using the penetrant testing method:
  1. An indication is defined as the presence of detectable bleed-out of the penetrant liquid from the material discontinuities appearing at least 10 minutes after the developer has been applied (see Note 1).
  2. Relevant indication: Only indications which have any dimension greater than 1,5 mm shall be considered relevant for the categorisation of indications.
  3. Non-linear indication: an indication with a largest dimension less than three times its smallest dimension (i.e. l < 3 w).
  4. Linear indication: an indication with a largest dimension three or more times its smallest dimension (i.e. l ≥ 3 w).
  5. Aligned indications:
    1. 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.
    2. Linear indications form an alignment when the distance between two indications is smaller than the length of the longest indication.
Note 1: Where there is uncertainty regarding the dimensions of the bleed-out indication size, either due to a large number of small, grouped indications, or an indication experiences excessive bleed-out, the penetrant testing process shall be repeated by strictly following the procedure. In exceptional circumstances, whereby the indication size cannot be accurately determined, the actual discontinuity size may be further examined using visual inspection methods, and augmented (if and where necessary) with the aid of magnification instruments, to determine the actual size of the discontinuity, as visible on the surface of the material.

5.5.9 This further examination is to be agreed with the Surveyor, and the Surveyor may, where deemed necessary, request furtherNDE to ascertain the extent of indications, which may include volumetric testing.

5.5.10 Where required by LR, or deemed necessary by the manufacturer and Surveyor, further volumetric NDE (e.g. radiographic and/or ultrasonic testing) is to be carried out. The acceptance criteria are to be agreed between the manufacturer and LR in accordance with a recognised standard. Note: due to the attenuating effect of ultrasound within austenitic steel castings, ultrasonic testing may not be effective in some cases, depending on the shape/type/thickness, and grain-growth direction of the casting.

5.5.11 Advanced NDE methods, as described in Ch 1, 5.11 Advanced NDE methods, may be applied to steel castings for propellers, as appropriate to the material type, thickness, complexity and geometry, as a substitute for, or complementary to, conventional ultrasonic or radiographic testing.

5.5.12 Static balancing is to be carried out on all propellers in accordance with the approved drawing. Dynamic balancing may be necessary for propellers running above 500 rpm.

Table 4.5.3 Allowable number and size of relevant indications in a reference area of 100 cm2(see Note 1)

Severity Zones Max. total number of indications Type of indications (see Note 2) Max. number of each type (see Notes 3 and 4) Max. acceptable value for 'w' or 'l' of indications (mm) (see Note 2)
A 7 Non-linear 5 4
    Linear 2 3
    Aligned 2 3
B 14 Non-linear 10 6
    Linear 4 6
    Aligned 4 6
C 20 Non-linear 14 8
    Linear 6 6
    Aligned 6 6
Note 1. The reference area is defined as an area of 0,01 m2, which may be square or rectangular, with the major dimension not exceeding 250 mm. The area shall be taken in the most unfavourable location relative to the indication being evaluated.
Note 2. Non-linear, linear and aligned indications are defined as follows:

Note 3. Single non-linear indications less than 2 mm in Zone A and less than 3 mm in other zones are not considered relevant.
Note 4. The total number of non-linear indications may be increased to the maximum total number, or part thereof, represented by the absence of linear or aligned indications.

5.6 Rectification of defective castings

5.6.1 The rectification of defective castings is to be undertaken in accordance with Ch 4, 1.11 Rectification and dressing of castings and the following paragraphs.

5.6.2 Removal of defective material is to be by mechanical means, e.g. by grinding, chipping or milling. The resultant grooves are to be blended into the surrounding surface so as to avoid any sharp contours. Complete elimination of the defect is to be verified by penetrant testing, or magnetic particle testing as appropriate.

5.6.3 Grinding in severity Zone A may be carried out to an extent that maintains the blade thickness. Repair by welding is generally not permitted in Zone A and will only be allowed after special consideration.

5.6.4 Defects in severity Zone B that are not deeper than t/40 mm (t is the minimum local thickness according to the Rules) or 2 mm, whichever is the greater, are to be removed by grinding. Those defects that are deeper may be repaired by welding subject to prior approval of the Surveyor.

5.6.5 Repair welding is generally permitted in severity Zone C.

5.6.6 Welds having an area of less than 5 cm2 are to be avoided. The maximum surface area of repairs is to be in accordance with Table 9.1.3 Permissible rectification of new propellers by welding in Chapter 9.

5.6.7 Welding procedures are to be qualified in accordance with Ch 12, 3 Specific requirements for stainless steels with the following exceptions and additions:
  1. Three macro specimens representing the start, middle, and end of test weld are to be prepared and tested. The hardness readings are to be taken from the macro specimen representing the start of weld.
  2. The mandrel diameter for bend test should be four times the thickness of test specimen for martensitic stainless steel.
  3. The qualification range for base material thickness is given in Table 4.5.4 Thickness approval range. The test assembly is to consist of cast material and its thickness should be no less than 15 mm.
  4. The qualification is only valid for the base material grade used for the test assembly.
  5. Approval for a test made in any position is restricted to that position.
  6. The approval is only valid for the welding consumable trade name used in the welding procedure test.

Table 4.5.4 Thickness approval range

Test assembly thickness, t (mm) Thickness range approved
15 < t ≤ 30 3 mm to 3t
t >30 mm 0,5t to 2t or 200 mm, whichever is greater

5.6.8 Welding is to be in accordance with the approved specification, see Ch 4, 5.1 Scope 5.1.3.

5.6.9 After weld repair, the propeller or blade is to be heat treated in such fashion as will minimise the residual stresses. For martensitic stainless steels, this will involve full heat treatment as specified in the approved specification. Special consideration will be given to alternative heat treatment recommended by the manufacturer.

5.6.10 LR reserves the right to restrict the amount of repair work accepted from a manufacturer when it appears that repetitive defects are the result of improper foundry techniques or practices.

5.6.11 All welds are to be inspected by the appropriate NDE method, see Ch 4, 1.7 Visual and surface Non-Destructive Examination.

5.7 Identification

5.7.1 Castings 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 castings which have been accepted:

  1. Identification mark which will enable the full history of the item to be traced.

  2. Type of steel, this should include or allow identification of the chromium and nickel contents.

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

  4. Personal stamp of Surveyor responsible for the final inspection.

  5. LR certificate number.

  6. Skew angle, if in excess of 25°.

  7. Ice class symbol, where applicable.

  8. Date of final inspection.

5.8 Certification of materials

5.8.1 In addition to the requirements in Ch 4, 1.13 Certification of materials, the manufacturer is to provide the Surveyor with a written statement giving the following particulars for each casting:

  1. Description of casting with drawing number.

  2. Diameter, number of blades, pitch, direction of turning.

  3. Skew angle, if in excess of 25°

  4. Final mass.

  5. Vessel identification, where known.

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