DL/T 764.3-2025 in English

Technical Evolution Analysis of the DL/T 764.3-2025 Standard

Blind Pins, as key fastening components in power fittings, play a vital role in the safe operation of transmission lines. The DL/T 764.3-2025 standard replaces the DL/T 1343-2014 version, marking a further improvement in the technical framework for power fitting fasteners. This revision represents 11 years of technical accumulation and reflects the power industry's continuously increasing requirements for equipment reliability.

Scope of Application and Technical Framework of the Standard

This document applies to Blind Pins for power fittings in sizes M8 to M82, covering all voltage levels, from distribution to ultra-high voltage transmission. The standard establishes a comprehensive technical specification system, including core content such as type and size, material requirements, performance indicators, inspection methods, and packaging labeling.

In-depth analysis of closed pin model system and technical parameters

The standard divides closed pins into nine specifications: A0, A, B, C, D, E, F, G, and H according to the applicable bolt specifications, forming a complete model system. The new model A0 is designed for small-size bolts M8 and M10, while the H type covers the application of extra-large bolts M80 and M82, meeting the diverse needs of power grid equipment.

The optimization of key dimensional parameters reflects the accumulation of technological progress:

• Refined tolerance control: The tolerance range of R and t is added to 0~+0.1mm, and the tolerance range of l1, l2, and l3 is 0~+1.0mm to ensure installation and fit accuracy
• Optimized structural dimensions: The dimensional parameters of code A corresponding to t and G corresponding to l1 and l2 are modified to improve structural rationality
• Standardized representation: The model representation method is "code+d", such as A02.2, A2.8, and B3.6, which is easy to identify and manage

Material technical requirements and performance improvement

The standard clearly stipulates that the material of closing pins should be austenitic stainless steel specified in GB/T 1220, and its corrosion resistance should be no less than 06Cr19Ni10. This requirement significantly extends the product's service life in harsh environments, making it particularly suitable for use in highly corrosive areas such as coastal areas and industrial pollution.

Major Updates to Mechanical Performance Indicators:

• Hardness Requirements Have Been Upgraded: The Brinell hardness requirement has been revised from a minimum of 130 to an average Vickers hardness of at least 150, resulting in a more precise testing method.
• Bending Resistance Requirements Have Been Clarified: No cracking should occur after the bending test, ensuring structural integrity during installation and use.
• Pull-out Load Requirements Have Been Improved: New pull-out load requirements for closed-end pins, designated A0 and H, have been added, forming a comprehensive load system.

Quality Inspection System and Acceptance Specifications

The standard establishes a tiered inspection system, categorizing testing into material assessment and sampling tests. Material assessment tests, including hardness and bend tests, focus on the essential properties of the manufacturing material, while sampling tests focus on manufacturing quality control.

The sampling and repeated testing procedure reflects the rigor of quality control: if the initial test fails, repeated testing is allowed according to specific rules, which not only ensures quality but also avoids excessive testing.

Standard Implementation Recommendations and Engineering Applications

Selection Guidelines

In power engineering design, the selection of closed pins should follow the following principles: determine the corresponding closed pin model based on the bolt specifications, select the appropriate material based on environmental corrosion, and determine the appropriate size based on the installation space. It is particularly important to note that when using closed-end pins in anti-dance and anti-vibration hardware such as spacers and anti-vibration hammers, the closed-end pins should automatically open after being inserted into the bolt pin hole to ensure reliable locking.

Quality Control Key Points

During the manufacturing process, key controls should be implemented: incoming material inspection to ensure that the stainless steel composition meets the requirements, stamping process control to avoid cracks and burrs, heat treatment process to ensure hardness uniformity, and dimensional inspection to ensure that tolerances meet standards. During acceptance, the user unit should focus on surface quality, dimensional conformity, and necessary performance tests.

Installation and Use Specifications

During installation, the two legs should be inserted into the pin hole tightly together according to the requirements of the standard diagram, ensuring that the two legs automatically open after insertion. The opening state should be checked after installation to ensure the locking effect. During maintenance and replacement, special tools should be used for extraction operations to avoid damaging the hardware components.

Technological Development Outlook

With the construction of smart grids and the development of transmission technology, closed-end pin technology will develop towards high performance, standardization, and intelligence. Possible future technological evolutions include: the application of new materials to improve corrosion resistance and mechanical properties, structural optimization to adapt to higher voltage levels, and the integration of intelligent monitoring technologies to achieve visual status management. The implementation of DL/T 764.3-2025 will lay a solid foundation for these technological developments.

As an important component of the power fittings and fasteners system, this standard, together with other parts of DL/T 764, establishes a complete technical specification for power fittings and fasteners, which is of great significance for improving the safe operation of power grids. All relevant units should fully understand the technical requirements of the standard and strictly adhere to it in design, manufacturing, inspection, and use to ensure the safe and reliable operation of power facilities.