Section 7 Welding qualification requirements for high strength steel for special marine applications

7.1.1 The purpose of this Section is to present a goal-based approach to the requirements for high strength steels for special marine applications, not covered elsewhere in the Rules for the Manufacture, Testing and Certification of Materials, July 2022. Whilst the primary intent of the application of the welding qualifications listed herein is for pressure vessels/submersible craft intended for human occupancy, use and application of these qualifications for other constructions may be specially considered within the scope of the goal-based framework.

7.1.2 The goals, functional requirements and performance requirements listed herein relate to welding qualifications required to be performed for construction.

7.1.3 In addition to this goal-based framework, the relevant requirements of the Rules for the Manufacture, Testing and Certification of Materials, July 2022 are to be complied with for certification. In order to satisfy the goal-based framework in this Chapter, it is necessary to comply with the other applicable Rules related to materials, manufacture, testing, survey and classification.

7.1.4 The list of goals is as follows:

1. Welding qualifications shall demonstrate that the resulting weld joints have the integrity to minimise the risk of loss of the structure due to failure.
2. Welding qualifications shall demonstrate that the resulting welds minimise the hazard to persons, assets or environment in any foreseeable operating conditions.

7.1.5 The list of functional requirements (FR) is as follows:

1. Welding procedure qualification tests shall demonstrate acceptable chemical and mechanical properties for the application and withstand the applied design loads.
2. Welds produced in accordance with a qualified weld procedure and by qualified welders shall be able to function in a safe and acceptable manner, for compliance with the manufacturing and design criteria.

7.1.6 The list of performance requirements (PR) is as follows:

1. For welding procedure qualification tests, the mechanical properties for category A and B welds shall comply with the requirements stated in Table 12.7.1 Mechanical property acceptance requirements for butt welding in plate (in welds that form part of the pressure hull boundary, and tensile loading under normal submarine operation) for applicable Material Class Special Application 1 and 2.
2. When required by a specific project or specified testing regime, the surface crack extension from flawed bulge explosion (FBE) tests is to be not greater than 50 mm. Where indications of laminar flaws are detected within 10 mm of the tension surface, and they extend to within 50 mm of the fatigue cracked notch, then there is the potential for them to have influenced the shock loading of the bulge panel flaw. In such cases the FBE test is not considered valid.
3. When required by a specific project or specified testing regime, four of the five crack tip opening displacement (CTOD) test results must be greater than 0,1 mm. One value may be less than 0,1 mm provided it is greater than 0,07 mm.
4. For welding procedure qualification tests, the mechanical properties for category C and D welds shall comply with the requirements stated in Ch 12, 2 Welding procedure qualification tests for steels except that Charpy impact test minimum energy requirements are to meet the requirements of Table 12.7.1 Mechanical property acceptance requirements for butt welding in plate (in welds that form part of the pressure hull boundary, and tensile loading under normal submarine operation) for applicable Material Class Special Application 1 and 2.
5. For welder qualification tests, the results from visual inspection and non-destructive examination (NDE) are to be in accordance with Ch 12, 2.5 Non-destructive examination (NDE) 2.5.5.
6. Welders shall demonstrate that they can consistently meet the above requirement.

7.2.1 The requirements of this Section relate to the welding qualifications of high strength steels intended for use in special marine applications, which are not covered elsewhere in this Chapter.

7.2.2 An accepted solution for satisfactorily meeting the goal-based framework is specified in sub-Sections Ch 12, 7.2 LR accepted solutions for welding qualifications for high strength steel for special marine applications to Ch 12, 7.6 Welder qualification of this Section.

7.2.3 The application, in entirety, of the prescriptive content in this Section (including any references leading out) is considered to meet the listed goals.

7.2.4 Alternative proposals for meeting the goal-based framework in Ch 12, 7.1 Goal-based framework will be specially considered.

7.2.5 The requirements presented herein represent an accepted solution for welding qualifications, certified for use High Strength Steel – Special Application 1 and 2, and the appropriate consumable grade for the relevant material class.

7.3.1 In addition to the requirements of this sub-Section, fulfilment of an accepted solution also requires compliance with the relevant Sections of the Rules for the Manufacture, Testing and Certification of Materials, July 2022, specifically:

• Ch 1 General Requirements,
• Ch 2 Testing Procedures for Metallic Materials,
• Ch 12, 1 General qualification requirements,
• Ch 12, 2 Welding procedure qualification tests for steels and
• Ch 12, 5 Welder qualification tests,

regarding approval and manufacture, testing, inspection and general requirements for welding qualifications.

7.3.2 Unless stated below, qualification of welding procedures is to be in accordance with Ch 12, 2 Welding procedure qualification tests for steels and the qualification of welders is to be in accordance with Ch 12, 5 Welder qualification tests.

7.3.3 Welding procedures for High Strength Steel – Special Application 2 may be approved with a weld metal strength lower than the minimum specified for the base material, i.e. undermatched welding. Where welding procedures are approved for undermatched welding, the requirements specified in Ch 13, 10.3 General requirements 10.3.5 are to be followed.

7.4.1 Welding procedure qualification tests are to be performed to qualify welding for specific categories, as defined by Table 12.7.2 Weld categories of high strength steel for special marine applications.

7.4.2 For each weld category the following welding procedure qualification tests are to be completed:

Category A: Test assemblies in accordance with Ch 12, 7.4 Welding procedure qualification tests 7.4.4. In accordance with specific project requirements an additional test assembly is to be prepared for FBE testing.

Category B: Test assemblies in accordance with Ch 12, 7.4 Welding procedure qualification tests 7.4.5. In accordance with specific project requirements an additional test assembly is to be prepared for Crack Tip Opening Displacement (CTOD) testing.

Category C and D: Two test assemblies from the lowest and highest heat input positions in accordance with Ch 12, 2 Welding procedure qualification tests for steels except that Charpy impact test minimum energy requirements are to meet the requirements of Table 12.7.1 Mechanical property acceptance requirements for butt welding in plate (in welds that form part of the pressure hull boundary, and tensile loading under normal submarine operation) for applicable Material Class Special Application 1 and 2

7.4.3 High Strength Steel – Special Application 2 butt weld applications are to be qualified via Category A and B routes. Fillet weld applications may be qualified via Category C and D routes.

7.4.4 A test assembly in accordance with Figure 12.7.1 Butt welds in plate (category A and B) is to be prepared and sectioned for mechanical testing. The assembly is to simulate production conditions including minimal restraint and in the worst position. Panels welded in the vertical up position will automatically qualify the procedure for all positions.

Figure 12.7.1 Butt welds in plate (category A and B)

7.4.5 Two sets of Charpy V-notch impact tests are required, notched in the weld centre. One set is to be taken from 2 mm below the surface of side 1 and one set from 2 mm below the surface of side 2.

7.4.6 The Charpy V-notch impact fracture appearance is to be determined in accordance with ISO 148-1 or another recognised National Standard.

7.4.7 All weld tensile samples are to be taken from both sides of the weld. The test specimens are to be of a circular cross- section, seeCh 11, 2.1 Dimensions of test specimens 2.1.1. Where necessary, reduced size test samples in accordance with ISO 6892-1: Metallic materials – Tensile testing – Part 1: Method of test room at temperature or other recognised National Standard are permitted to ensure samples are extracted wholly within the weld metal.

7.4.8 When the procedure is for thin plates, below 20 mm, the Charpy V-notch impact and tensile requirement is to be taken from the mid-section of the weld.

7.4.9 The results of tensile and impact tests for test assembly A are to comply with the performance requirements of Table 12.7.1 Mechanical property acceptance requirements for butt welding in plate (in welds that form part of the pressure hull boundary, and tensile loading under normal submarine operation) for applicable Material Class Special Application 1 and 2.

7.4.10 When the project requires specifies explosion and/or fracture toughness properties, further test assemblies as per Figure 12.7.1 Butt welds in plate (category A and B) are to be welded to facilitate FBE and crack tip opening displacement tests.

7.4.12 Number of specimens and method of testing for FBE is to be agreed with the project authority.

7.4.13 FBE tests results are to comply with Ch 11, 10.1 Goal-based framework 10.1.6.(b)

7.4.14 Two sets of five crack tip opening displacement test specimens are required. One set is to be notched in the first side of the weld and one set notch in the second side of the weld. Both sets of specimens are to be notched in the weld centre. For 20 mm thick test plate the dimensions are to be W = 40 mm, B = 20 mm and the notch is to be through the weld thickness and 20 mm deep. For the 50 mm test plate they are to be no less than 45 mm square with a crack depth to width ratio (a/W) of 0,3. Tests are to comply with Ch 2, 6 Crack tip opening displacement tests and tested at −5°C.

7.4.15 Crack tip opening displacement test results are to comply with Ch 11, 10.1 Goal-based framework 10.1.6.(c)

7.5.1 A WPS for High Strength Steel – Special Application 2 which is approved for undermatched welding, shall specify the maximum root gap for which the WPS is applicable. This gap should be set prior to completion of the qualification test and in consultation with the project authority. The requirements specified in Ch 13, 10.3 General requirements 10.3.5 are to be followed, in addition if actual production welding root gaps are greater than as specified in the WPS, the project authority should be consulted.

7.6.1 The test plate thickness is to be no less than 20 mm with the exception that fillet weld test piece is to have a standing test piece of 16 mm, a passing member of equal or greater thickness and a leg length of 11 mm. Mild steel plates may be used in place of high strength steel plates.

7.6.2 Each completed test weld is to be examined and tested in accordance with the requirements of Table 12.7.3 Welder qualification test requirements for high strength steel for special marine applications.

7.6.3 The results of visual and NDE are to comply with Ch 12, 7.1 Goal-based framework 7.1.6.(e)

7.6.4 To retain a qualification, the welder shall have one weld examined using both radiography and ultrasonic examination, every six months.