4. RCC-M technical scope vs ASME III:Technical differences Equivalent but not identical! Reconciliation needed for the manufacturer
1 Material: ASME uses generic prequalification/ RCC-M uses prototype qualification (M140)
2 Material Stress Limits: ASME Section III, Class 2 and 3 allowable stresses are now up to 15% higher than those of the RCC-M Code, because Section III stress limits are now based on a design factor of 3.5 rather than 4
3 Material: RCC-M permits use of only very low carbon stainless steels with nitrogen limits. Determination of sensitivity to IGSCC, by corrosion testing, is required if the carbon content exceeds specified limits (0.03-0.04%). ASME Section III leaves material selection and IGSCC concerns to the Owner or Fabricator.
4 Material: RCC-M requires elevated-temperature tensile testing (base metal, weld metal, procedure qualifications) to confirm the elevated-temperature tensile and yield strengths for each heat/lot and welding procedure/ ASME relies on properties from representative heats to establish allowable stresses at elevated temperatures. Design factors compensate for unknowns and variations
5 Material: RCC-M requires impact testing with little regard for material composition or experience. It requires impact testing of materials that are exempted from testing by ASME Section III because of their inherent high toughness, such as austenitic stainless steel filler metal. These tests are not required by ASME Section III.
6 Material: RCC-M imposes a delta ferrite limit of 5-15%. The Section III limit is 5FN minimum. Section III does not have a maximum limit. High delta ferrite has not resulted in failure./ RCC-M requires corrosion testing if the carbon content exceeds 0.035%. ASME Section III does not require corrosion testing.
7 Design: Reinforced Openings, Class 1 Vessels - Same design approach, but RCC-M requires full stress analysis of openings, in addition to reinforcement calculations./ ASME Class 1 Piping
Same design approach, but RCC-M requires full stress
8 Design: Fatigue at Discontinuities - Same basic approach in both Codes, but RCC-M has add new detailled conditions of use of fatigue curves.
9 Welding qualification: RCC-M requires production weld test coupons. In most cases, one coupon per component, per WPS, per welder. ASME Section III does not require such coupons.
RCC-M welding procedure qualification for repair welds in castings must be performed using cast material. ASME Section III permits use of other product forms, such as plate. For Asme, procedure qualification product form has not been associated
10 Welding Qualification and Examination: RCC-M requires the welding procedure qualification test coupon to be examined in accordance with the production weld joint NDE requirements and to meet the applicable acceptance criteria. ASME Section III does not require this examination. ASME considers taht examination of the production joint proves weld quality.
RCC-M permits no undercut. ASME Section III permits 1/32 in. (1 mm). ASME considers that undercut has not been associated with weld failure.
11 Examination: RCC-M requires liquid penetrant examination of all Class 1 weld preparation surfaces prior to welding. In addition, the root pass of all welds not requiring final volumetric examination (e.g., fillet or partial-penetration welds) is to be examined using the liquid penetrant method. These examinations are not required by ASME Section III. ASME considers that absence of such exams has not been associated with weld failure.
12 Examination: the RCC-M Code requires radiographic and surface examination of piping butt welds in all Classes. ASME Section III requires the same for Class 1, but less examination for Class 2 and 3 piping butt welds. ASME considers that higher design factor for Classes 2 and 3 compensates the reduced examination requirements.
13 Non-pressure-retaining Items: RCC-M specifies some requirements for non-pressure-retaining items, such as pump shafts and impellers, which are exempted from the ASME Section III requirements because they do not affect pressure boundary integrity. ASME considers that examination of these items have to be specified by the Owner or designer.
14 Hydrostatic Testing: RCC-M specifies higher hydrostatic test pressures than ASME Section III, especially for castings. Because the hydrostatic test does not exceed the material yield strength, the higher pressure adds no benefit. For cast components, RCC-M requires a hydrotest at 1.5 times design pressure times the ratio of the yield strength at the test temperature to the yield strength at the design temperature, up to 1.8 times design pressure. For forgings, the required test pressure is 1.25 times the yield strength ratio, not to exceed 1.5 times design pressure. The ASME Section III test pressure is 1.25 times design pressure. No failures have been attributed to a lower test pressure.
ASME Code for implementation in EPR– ASME Semina in RSA r –October 7th, 2008