Curve КIR = f (Т - RTNDT) is used in the ASME Code for brittle fast fracture analysis. The curve is based on the lower boundary of the КI critical values data, obtained by the static, dynamic, and crack brake tests. RTNDT temperature is determined in drop weight tests and Charpy test by impact fracture toughness and transverse expansion values.
Curves KIC = f (T - Tk) are used in PNAE G-7-002-86. The curves are based on the lower-boundary KIC critical values data, obtained during static loading of samples from vessel steels and their welds.
There is also a generalized curve for other steel grades. The critical nil-ductility temperature Tk0 is determined by impact bending test results. The Tk temperature is determined from Tk0 by introducing the temperature shifts ΔTk as a result of radiation, thermal, and fatigue aging.
In most cases, Tk temperature is slightly above RTNDT temperature.
For simplicity of curve comparison, assume that RTNDT = Tk. The curve comparison for PNAE G-7-002-86 (Figures 5.14 − 5.17) and the ASME Code (Figure G-2210.1) shows that the generalized curve used in PNAE G-7-002-86 (Figure 5.17) is close to the ASME Code curve. The remaining curves for the materials used in reactor pressure vessel manufacture in Russia lie to the left of the ASME Code curve. This may be a result of the difference in properties for the materials used in the Russian Federation and the USA for reactor pressure vessel manufacturing.
A normal to maximum stress direction surface crack was adopted as a postulated defect in ASME G-2120. The crack depth is assumed to be 1/4 of wall thickness with a length equal to 1.5 of wall thickness for 101.6 to 304.8 mm thicknesses. The same crack for 304.8 mm thickness is taken for thicknesses of more than 304.8 mm. A 25.4 mm depth crack is taken for thicknesses of less than 101.6 mm. Smaller defect sizes may be used if reasonable assurance can be provided that large cracks cannot be found in the construction.
Semi-elliptical surface cracks of 0.25 wall thickness depth and 0.75 wall thickness length are specified in PNAE G-7-002-86 (5.8.5.2) without any thickness restrictions.
In the ASME Code, calculated crack length is larger than in PNAE G-7-002-86, but crack depth is the same.
Safety factors equal to 2.0 for stress intensity factor identified by primary stresses, and 1.0 for stress intensity factor identified by secondary stresses, are specified in ASME Code G-2215. A safety factor of 2.0 is introduced in PNAE G-7-002-86 (5.8.3.1) regardless of the nature of the stress. In addition, a temperature margin of 30°C is introduced.
Safety factors equal to 1.5 for stress intensity factor identified by primary stresses, and 1.0 for stress intensity factor identified by secondary stresses, are specified in ASME Code G-2400 for hydraulic test conditions; also, a temperature margin of 60°F (33°С) for RTNDT is introduced. A safety factor of 1.5 is introduced in PNAE G-7-002-86 (5.8.3.1) regardless of the nature of the stress. In addition, a temperature margin of 30°C is introduced.
8.6 Fabrication and Welding
This subsection presents the results of comparisons of the basic provisions pertaining to welding and manufacturing.
ASME and PNAE standards are similar in fundamental principles pertaining to qualification of welding processes; both describe an organizational approach for certification and qualification of welding processes; define of essential parameters fundamental for development of welding process specifications; provide heat treatment requirements (pre-heating, control of temperature during welding and heat treatment after welding); and specify test and examination requirements for qualification of welding processes and examination of weld joint quality.
Comparative analysis of concepts and definitions from ASME and PNAE G-7 are presented in Table 59.
Table 59—Fundamental Concepts of ASME Code Section IX and PNAE G-7
ASME Code PNAE G-7 Comments to PNAE G-7
Specification of the welding
process Industrial engineering
documentation Developed by manufacturer. Provides guidance to manufacturing personnel.
Qualification of the welding
process Industrial certification of the
welding technology Executed on the basis of the certification program of welding technology and industrial engineering documentation.
Both documents are developed by the manufacturer who also carries out the certification.
Welding procedure
qualification report Report of industrial certification of the welding procedure
Report must include:
• all regulated parameters of welding technology;
• all results of tests obtained by destructive and nondestructive examination methods.
ASME Section IX specifies the list of welding parameters (see Table 60) that must be addressed in the welding procedure specification. The type and the number of parameters specified in this list are identical to those to be provided in the industrial engineering documentation in accordance with PNAE G-7.
Table 60—List of Welding Technology Parameters Specified in ASME Code and PNAE G-7
Welding Technology Parameters ASME Code PNAE G-7
Structural shape of a joint Requirements are defined by
manufacturer PNAE G-7-009-89
Base metal ASME Code Section II
ASTM Specifications ASME Code Section IX
PNAE G -7-008-89 PNAE G -7-009-89
Welding consumables ASME Code Section II ASW Specification ASME Code Section IX
PNAE G -7-009-89
Initial heating conditions Requirements are defined by
manufacturer PNAE G -7-009-89
Sequential heat treatment Requirements are defined by
manufacturer PNAE G7-009-89
Electrical characteristics Requirements are defined by
manufacturer PNAE G7-009-89
(recommended) Technique of welded joints Requirements are defined by
manufacturer PNAE G-7-009-89
The numerical values, ranges, and descriptions of changes in significant variables that change conditions of welding and affect mechanical properties
ASME Code Section IX Not provided
The numerical values, ranges, and descriptions of changes in significant variables that affect manufacturing joint quality
ASME Code Section IX Not provided
Comparison of the types of test methods and specimens required by the PNAE G-7-010-89 and ASME codes for various types of welded joints during qualification of the welding process is presented in Table 61. This table indicates that requirements defined by both Codes relative to basic examination methods are virtually the same. One significant difference noted from this table is that the ASME Code includes drop weight testing but PNAEG-7-010-89 does not.
Table 61—Types of Tests and Examinations Used for Qualification of Welding Procedures
Type of Testing or a
Control Type of a Sample
Availability in Standards ASME
Code PNAE G-7-010-89
1. Tensile test Flat + +
Segmental (for tubes of large diameter) + +
Cylindrical + +
Flat section of a tube + +
2. Bend test Transversal side bend + –
Transversal, surface of a weld is outside + +
Transversal, root of a weld is outside + +
Longitudinal, surface of a weld is outside + +
Longitudinal, root of a weld is outside + +
3. Bending impact test With V-notch for Charpy tests + +
4. Drop weight tests of
notched samples By specification ASTM E 208 + –
5. Tests of fillet welds Samples for examination and macroexamination + +
Samples for collapse tests + –
6. Radiographic
examination Test welded joint + +
7. Tests on welded studs Samples for bend test or for flattening from
above + –
Samples for torsion and tensile tests + –
8. Examination by liquid
penetrant Test welded joint + +
Notes:
+ - provided by standards – - not provided by standards
Another significant difference between the ASME and PNAE-G7 relative to welding is the requirement for destructive testing of production welds which is obligatory according to Russian regulatory documents. While ASME Design Specifications may define supplemental requirements requiring destructive examination of particular types of weld joints, ASME Section III does not define requirements for destructive examination of welds beyond the testing required to support welding procedure qualification. Likewise, whereas the ASME approach for procurement and certification of welding consumables is based on assessment and qualification of approved suppliers and certification of materials by the Supplier, PNAE G-7-010-89 requires each lot of materials to be independently tested by the equipment manufacturer prior to use.
8.7 Examination
This section contains the comparison of the PNAE G-7-010-89 and the ASME Code requirements and acceptance standards for examination of welded joints.
The ASME Code more clearly stipulates the required examination methods and extent of examination depending on the types of welded joints (butt, corner with full penetration or with constructive gap, longitudinal or circular, etc.) for elements of all classes of equipment and piping. Nevertheless, the PNAE G-7-010-89 and the ASME Code approaches to classification and treatment of defects is virtually identical; the most dangerous defects − cracks, lack of fusion, and incomplete fusion − are not permitted by either and implementation in practice is similar.
Acceptance standards for production welds in the PNAE G-7 Code are, in general, consistent with those of the ASME Code for respective types of examinations but, on a specific case-by-case basis, acceptance criteria for specific examinations may be more or less conservative.
Both PNAE G-7 and the ASME Code apply the same nondestructive examination methods:
• Visual
• Liquid Penetrant Examination
• Magnetic Particle Testing
• Radiography
• Ultrasonic Testing
Table 62 presents the mandatory methods and extent of examination from both Codes for different weld joint categories.
Table 62―Methods and Amounts of Welds Examination According to PNAE G-7-010-89 (Category I) and ASME Code (Class 1 Subsection NB)
Type of Weld Joint Code Thickness or Diameter, mm
The data from Table 62 indicates that the extent of NDE for production weld joints (radiography, ultrasonic inspection, liquid penetrant, and magnetic particle inspection) of Category I according to PNAE G-7-010-89 is generally equivalent to that required by ASME Code Class I components.