8 PNAE G-7 VERSUS ASME BPVC Section III COMPARISON
8.7.6 Offset of Weld Edges in Butt Weld Joints
Acceptance standards for offsets of edges in butt weld joints in the ASME Code and PNAE G 7-010-89 are shown in the Figure 45 as the dependence of maximum allowable offsets in longitudinal (a) and circular seams (b) vs. thickness of welded elements.
These graphs show that the PNAE G-7 criteria for maximum offset are generally more stringent than those of the ASME Code; for longitudinal seams in the thickness range from 40 to 70 mm, requirements of the ASME Code are more stringent than those of PNAE G-7-7-010-89.
Co nv ex ity of w el d se am ,m m
1 2 3 4 5 6 7
25 50 75
Thickness of welded elements, mm PNAEG-7 category I, II and III
ASMECode class 1,2 and 3 1
2 3 4 5 6 7
25 50 75
Thickness of welded elements, mm PNAEG-7 category I, II and III
ASMECode class 1,2 and 3
Figure 45—Dependence of Maximum Allowable Edge Offsets in Longitudinal (a) and Circular Seams (b) vs. Thickness of Welded Elements
M ax im um al lo w ab le ed ge s of fe st ,m m 1 2 3 4 5 6 7
25 50 75
PNAEG-7 category I, II иIII ASMECode class 1,2 and 3
8 9
b) circumferential welds of vessels 1
2 3 4 5
25 50 75
PNAEG-7 category I, II и III ASMECode class 1,2 and 3
а) longitudinal weldseams M ax im um al lo w ab le ed ge s of fe st ,m m
Thickness of welded elements, mm
8.8 Pressure Tests
PNAE G-7-008-89 (5) and PNAE G-7-002-86 (5.4) establish approaches for determining the pressure test conditions to be applied after manufacturing, installation, and operation of equipment and NPP piping.
As is the case for ASME, a hydrostatic pressure test using water as a test media is preferred per PNAE G-7-008-89. Likewise, replacing the hydrostatic tests with pneumatic tests is allowed (PNAE G-7-008-89 5.1.3 and NB-6112) but, conditions for replacing hydrostatic tests with pneumatic tests are somewhat different.
The minimum testing pressure values required by PNAE G-7-008-89 and ASME NB-6000 are different.
According to PNAE G-7-008-89 (5.2.1−5.2.2), the pressure (Рh) of component hydraulic tests shall be:
Where: Р is design pressure of a component Т is design temperature of a component Тh is temperature of a component under test
[ ]
σTh is nominal allowable stress at temperature Тh[ ]
σT is nominal allowable stress at temperature ТValues
[ ]
σTh and[ ]
σTare determined according to PNAE G-7-008-86.If Р < 0.49 MPa, Ph > 1.5Р, but not greater 0.2 MPa.
Pressure of component pneumatic tests, according to PNAE G-7-008-89 (5.5.1), shall be:
[ ] [ ]
Twhere
[ ]
σTp is nominal allowable stress at temperature of the pneumatic tests.The test pressure to be applied for component hydrostatic tests must be at least 1.25 P according to ASME NB-6221(c), where Р is the design pressure.
Therefore, PNAE G-7-008-89 hydraulic test requirements are similar to those of ASME NB-6000.
Maximum allowable test pressure of components, as in PNAE G-7-008-89 and ASME NB-6000, is bounded by the conditions of strength and stability. Limitations of stress Pm are identical (Pm < 0.9Sy, where Sy is yield strength at test temperature). Limitations on stresses Pm + Pb from the ASME Code are less stringent.
Maximum stresses in bolts during testing are not specified in ASME NB-6000. According to PNAE G-7-002-86 (5.4.6), the average stresses in the bolts are limited to 0.7Sy.
Both ASME and PNAE G-7 define requirements relative to a lower limit test temperature to prevent brittle fracture. The PNAE G-002-86 (5.8.6) and PNAE G-7-008-89 (5.3) method of calculating this
The requirements of PNAE G-7-008-89 and the ASME Code for the preparation of components for pressure tests during manufacturing and mounting are similar to those defined in ASME.
According to PNAE G-7-008-89 (5.4.1), pressure measurement during the tests should be conducted using two independent calibrated pressure gauge or measuring channels. The total error of a pressure measurement during tests shall not exceed ±5% of the nominal value of the test pressure. Sensors and devices with a total error not exceeding ±3% of the maximum measured temperature must be applied for temperature measurement.
According to ASME NB-6412, common error of calibration and readout by using digital devices should not exceed 1% of test pressure value. Thus, according to the ASME Code, permissible error in measuring test pressure is less than in PNAE G-7-008-89.
According to PNAE G-7-008-89 (5.4.1) and ASME NB-6223, holding times at hydrostatic test pressure are equal (10 minutes), while holding times at pneumatic test pressure are different − 30 minutes for PNAE G-7-008-89 (5.5.6) and 10 minutes for ASME NB-6323.
Rules for interpretation of pressure test results in PNAE G-7-008-89 (5.7) and ASME NB-6224 and 6324 are similar with ASME requirements for controlling a leak being more detailed than in PNAE G-7-008-89.
8.9 Overpressure Protection
This section highlights the differences between the PNAE G-7 and ASME codes that relate to overpressure protection.
The prescriptions concerning overpressure protection are given in NB-7000 of ASME Code and PNAE-G-7-008-89 (6.2). These chapters differ significantly. The ASME Code has more detailed requirements for pressure relief devices. There are requirements for construction, installation, a list of devices permitted and prohibited for use, Overpressure Protection Report requirements, requirements for set pressures and relief capacity of pressure relief devices, requirements for certification including experimental and theoretical assessment of relief capacity in different environments, and marking and stamping rules.
Although overpressure protection requirements in PNAE G-7-008-89 have no structure and are less detailed, they generally cover the same aspects that are defined in NB-7000 of ASME Code, with some exceptions. For example, in PNAE G-7-008-89, there is no such term "Certificate Holder" and no certification requirements and methods for assessment of pressure relief devices capacity, while the ASME Code pays much attention to these things. Also, in PNAE G-7-008-89, there are no Overpressure Protection Report requirements with the exception of a requirement that the number, type, installation location, and other requirements for pressure relief devices must be specified in design documentation. Nevertheless, despite all their differences, both documents have similar requirements concerning the capacity of safety devices; as an example, according to the ASME Code, the total relieving capacity shall be sufficient to prevent a rise in pressure of more than 10% above the design pressure, while according to PNAE G-7-008-89, test pressure shall not exceed the level from which excess pressure is measured by more than 15%.
In addition, PNAE G-7-008-89 (6.2) includes some specific requirements that are not reflected in the ASME Code. These requirements particularly relate to equipment and piping with liquid metal coolant.
In conclusion, it is worth noting that the sections under consideration vary significantly in content and structure; however, despite the differences, there are similarities in terms of required capacity of pressure relief devices.
8.10 Overview of Quality Aspects
This section contains information about quality assurance on nuclear power uses in the Russian Federation.