Selection Guide for DBB Ball Valves in Urban Gas Transmission And Distribution Systems: The Synergistic Application of API 6D Standard And ISO 14313

Overall Structural Strength

Considering long-distance and large-flow gas transmission pipelines, it should be able to withstand situations like high pressure differences and complex external forces.
- The wall thickness of the valve body and the strength of connection parts are calculated meticulously and strictly regulated. Different pressure ratings (such as Class 150 - Class 2500) have minimum wall thickness requirements to prevent valves from being damaged by pressure fluctuations.

Mainly meeting various scenarios in urban gas transmission and distribution systems, focusing on good matching with surrounding pipe fittings and equipment, so that the valve remains stable as a whole and is not prone to failure when the pressure range is not large but operations are frequent.

Internal Flow Channel Design

The flow channel should be particularly smooth, made according to standard size ratios and surface finish requirements, allowing gas to flow through quickly, so that energy consumption and pressure losses are small, which is suitable for large-flow transmission in main lines.

On the basis of ensuring the basic smoothness of the flow channel, more attention is paid to how the shape of the flow channel can control the flow more accurately. Some tapered or expanding flow channel designs will be used to meet the situation where different users have different gas consumption requirements.

Valve Body Material

Commonly uses high-strength materials such as alloy steel and carbon steel. Since there may be corrosive substances (such as hydrogen sulfide) in natural gas and the pressure is high, the mechanical properties of materials such as tensile strength and toughness should be good, and there are strict requirements for chemical compositions.

Urban gas is relatively "clean". When selecting materials, in addition to sufficient strength, more attention is paid to the ability to resist corrosion caused by trace amounts of moisture and impurities, and the processing performance should be good to facilitate the manufacture of valve bodies with precise dimensions and shapes. Stainless steel and cast steel are commonly used.

Sealing Material

Select good materials such as polytetrafluoroethylene (PTFE) and flexible graphite. Their performances in terms of temperature resistance, pressure resistance, wear resistance, and anti-aging will be strictly tested to ensure that gas will not leak under long-term and high-pressure conditions.

Also attaches great importance to sealing. However, combined with the characteristic of frequent switching operations in urban gas systems, more emphasis is placed on the good elastic recovery and wear resistance of materials, so that the sealing can be restored immediately after each operation. Enhanced PTFE materials are widely used.

Shell Strength Testing

Clearly defines parameters such as test pressure and holding time. According to different pressure ratings, the shell strength is tested with a pressure higher than the rated working pressure (for example, 1.5 times) and maintained for about 15 - 30 minutes to check whether the valve body deforms or leaks, and it should be able to withstand extreme pressure conditions.

Verifies the strength within the commonly used working pressure range of urban gas. The test pressure is set according to a reasonable multiple of the actual use pressure (the multiple is slightly lower than that of API 6D). The focus is on whether the shell can always be durable and stable under frequent pressure changes, and the test cycle may be longer to simulate the situation of long-term actual use.

Sealing Performance Testing

Uses multiple methods such as the bubble method and pressure drop method to carefully detect the sealing performance under different pressures, medium flow directions, and other conditions, requiring extremely low leakage (such as zero leakage or micro leakage). For DBB ball valves with bidirectional shut-off functions, both directions of sealing must be reliable.

In addition to conventional detection methods, the sealing performance will also be tested when the valve is opened at different openings (simulating the process of flow regulation) to check whether there will be leakage when regulating the flow, so as to meet the requirements of both accurate control and safety in urban gas transmission and distribution systems. The allowable leakage range is determined according to specific application scenarios.

Valve Marking

Clearly mark the valve's specification model, pressure rating (such as writing Class 600), manufacturer, production date, and the mark indicating compliance with the API 6D standard on the valve body, so that it is easy to identify and trace in the petroleum and natural gas industries and is relatively standardized and universal.

Focus on marking important information related to urban gas transmission and distribution systems, such as the applicable gas type, flow characteristic parameters, and adjustment range. It also includes basic specification and manufacturer information to facilitate quick access to key information during installation, maintenance, and operation.

Documentation Provision

The manufacturer must provide detailed design drawings, material quality certificates, manufacturing process records, and various test reports (such as non-destructive testing reports, performance test reports, etc.) to prove that the valve complies with the API 6D standard, facilitating quality control and archiving by the purchaser and user.

In addition to conventional proof documents, more emphasis is placed on providing the flow regulation characteristic curve of the valve and the operation and maintenance manual (containing operation suggestions and precautions for urban gas systems) to help operators use and maintain the valve well and integrate it into the entire transmission and distribution system.