Similarity Analysis and Identification for Nuclear Power Valves

Abstract

This paper reviews the commonly used specifications and standards for nuclear power valve identification, examines the criteria for similarity and coverage, details the valve similarity identification, and provides practical recommendations for its application.

1. Overview

With advancements in the domestic manufacturing industry, the production of civil nuclear power facilities and equipment in China has gained increasing significance. The identification of domestic civil nuclear power valves primarily adheres to the international standard ASME QME-1 and the domestic energy industry standard NB/T20036.6-2011. ASME QME-1 is widely applied, with different versions utilized individually or in combination. Although these standards outline the valve similarity identification, they lack comprehensive guidance on practical implementation procedures.

2. Valve Similarity Principle

(1) The valves must be of the same type, for example, gate valves, globe valves, ball valves, and butterfly valves) and manufactured by the same producer on essentially identical production lines.

(2) The valve body and bonnet assembly must be similar in appearance and connection design, with primary differences limited to overall dimensions or weight.

(3) The valve actuators must be from the same product series.

(4) The valve seat structures and functions must be similar, maintaining consistency in structural design and geometric configuration.

(5) The valve stem or shaft packing must have similar geometric shapes and types.

(6) The actuator installation  must align with the same or equivalent approach.

(7) Functional accessories should be considered and installed in a similar manner, with differences in type, appearance, weight, and center of gravity acceptable within specified limits.

(8) Material differences in valve assembly components must be thoroughly assessed. Acceptable variations, excluding the packing, should include adjustments to identification parameters based on material yield strength and careful evaluation of material characteristics and combinations.

(9) Material changes are acceptable only if one of the following conditions is met:

• No frictional contact exists between the components.
• Friction contact points must be properly protected.
• Similar material combinations are used, such as ferritic, austenitic, or martensitic steel), and the hardness differential in the valve assembly to be identified meets or exceeds that of the identified valve assembly.
• At friction contact points, surface-hardened materials must not be replaced with unprotected austenitic stainless steel, martensitic steel with carbon steel, or surface-hardened materials with unprotected alternatives.
• Plastic or rubber components must remain unchanged unless modifications are shown not to affect operability or are validated through equivalent testing.

(10) The running clearance between all contacting or adjacent moving parts, such as the clearance between the valve disc and guide surface, must not produce more friction than in the identified valve assembly.

2.2 Valve Coverage Nominal Diameter Principle

The application of the expansion principle relies on strict adherence to the valve similarity principle outlined in Section 2.1.

(1) According to ANSI B16.41, the expansion principle allows for pressure ratings to range from 90% to 200% of the prototype’s pressure rating, and nominal diameters to range from 50% to 200% of the prototype’s nominal diameter.

(2) In ASME QME-1-2002, the expansion principle is classified based on nominal diameters as follows:

• Nominal diameter ≤ DN100
• DN100 < Nominal diameter ≤ DN500
• Nominal diameter > DN500

This classification defines the allowable range for extrapolating valve components. For example, a valve component with a nominal diameter of DN50 can be expanded to cover up to a nominal diameter of DN100.

(3) ASME QME-1-2007 removed the specific expansion requirements outlined in ANSI B16.41 and ASME QME-1-2002. Instead, it provides broader guidelines and methodologies for extrapolating valve identification.

3. Discussion on Valve Similarity Identification

3.1 Valve Similarity Principles and Identification Methods

(1) Valve Type and Series

Valves must belong to the same type and series, produced by the same manufacturer, and designed with consistent structural features. Within a series, pressure ratings may differ, but structural designs should remain unchanged. Key variations, such as differences in size and weight, are permissible as long as they do not affect functional integrity.

(2)Actuator Compatibility

Valve actuators should share the same power source and connection method. The connection must align with ISO 5211 standards or exhibit similar design characteristics. Common power sources include electric, pneumatic, hydraulic, electro-hydraulic, electromagnetic, and gas-liquid systems.

(3) Valve Seat Structure and Function

Consistency in sealing materials, hardness differentials, and sealing forms is essential. For example, parallel gate seals and wedge gate seals in gate valves differ significantly in both form and principle, even if sealing materials are identical. The manufacturing process of sealing surfaces, whether based on the parent material or enhanced through surface hardening methods such as surfacing or spraying, must also be analyzed for compatibility.

(4) Stem and Shaft Packing

Sealing for the valve stem or shaft must be consistent in structural design and material. Any differences in size and weight should solely result from variations in valve diameter.

(5) Actuator Installation

Actuator and valve assembly connections must comply with ISO 5211 standards or exhibit equivalent compatibility in line with the similarity principle.

(6) Functional Accessories

Functional accessories must be assessed for their installation method, dimensions, weight, and center of gravity, as these factors influence overall valve functionality. For example, if an accessory in the identified valve is heavier or has a larger eccentric center of gravity compared to the valve to be identified, its impact on operational performance should be carefully evaluated.

(7) Material Differences

Material differences between components must be thoroughly analyzed to ensure compatibility:

1. If the identified valve assembly has lower material yield strength but identical identification parameters, it may still be applicable to the valve to be identified.
2. If yield strength or parameters differ, testing or analysis must verify that these differences have minimal impact on functionality before extending applicability.
3. Material compatibility criteria include:
   • No frictional contact between components to minimize jamming risk.
   • Friction points optimized to maintain or enhance functional performance.
   • The valve to be identified must use materials at friction points that meet or exceed the durability and performance of those in the identified valve.
   • For non-metallic components, the compatibility of plastic or rubber materials must be validated through equivalent or stricter testing conditions.

(8) Clearances for Moving Parts

Moving part clearances must support functionality without increasing friction or the risk of jamming. It is essential to maintain consistent clearances or appropriate tolerance fits between the identified valve and the valve to be identified to ensure smooth operation and reliable performance.

3.2 Use of Valve Coverage Principle

The ASME QME-1-2007 standard removed the specific coverage principles for valve diameter outlined in the ASME QME-1-2002 standard and did not include the pressure rating coverage principles from ANSI B16.41. Instead, it retained only general principles and methods for extrapolating identification. Due to the significant variation in valve diameters within a series, manufacturers often lack adequate reference data when applying these guidelines. Consequently, the valve coverage principle typically excludes diameter and pressure rating factors for valves within the same series. This exclusion aligns with existing identification specifications and standards, ensuring compliance without introducing conflicts.

4. Use of Valve Similarity Principle

4.1 Similarity Identification Within the Same Series

• The valve similarity identification method is primarily designed for valves within the same series.
• Both the identified valve and the valve to be identified must belong to this series, whether they are being expanded or encompassed.
• Components within the same series typically exhibit similarities, with differences mainly limited to size and weight due to variations in diameter.

4.2 Handling Differences Between Valves

• Differences between the identified valve and the valve to be identified must be carefully analyzed to assess their impact on functionality.
• If the analysis indicates no negative impact or an improvement, the identified valve can be extended to cover the valve to be identified.
• If a negative impact is detected, additional testing, verification, or detailed analysis is required before proceeding.

4.3 Verification Methods for Differences

• For differences that negatively affect functionality, full-scale machine testing should be conducted.
• If full-scale testing is impractical, testing can be performed using a simulated part under comparable conditions.
• All verification methods must be robust and reliable to ensure accurate results.

4.4 Considerations for ASME QME-1-2007 and Later Versions

• When following ASME QME-1-2007 or later standards, it is essential to evaluate the principles of valve diameter and pressure rating coverage.
• These principles aid in prototype valve selection, minimizing risks and providing manufacturers with valuable technical references.
• For valves within the same series, coverage principles for diameter and pressure rating may be disregarded unless differences in appearance, structure, or performance arise due to these factors.

5. Conclusion

This discussion evaluates the application of the similarity principle from ASME QME-1 and NB/T20036.6-2011, along with the pressure rating coverage specified in ANSI B16.41, to extend the applicability of an identified valve to a valve under consideration. When using the similarity method, any differences must be thoroughly analyzed and addressed with appropriate measures to ensure the extension is validated.