API 6D refers to a specification developed by the American Petroleum Institute (API) for pipeline valves, specifically focusing on pipeline gate valves, plug valves, and check valves. It provides detailed guidelines for the design, materials, manufacturing, testing, and inspection of these valves used in the oil, gas, and petrochemical industries.

API 6D sets the standards for various aspects of the valves, including dimensions, pressure ratings, temperature ratings, materials of construction, end connections, and operational requirements. The specification ensures that the valves meet the necessary safety, reliability, and performance standards required for their intended applications.

Valves that conform to the API 6D standard are designed to withstand high-pressure and high-temperature conditions, provide tight shut-off, and offer reliable and efficient operation in pipeline systems. The specification also includes stringent testing and inspection procedures to verify the performance, quality, and integrity of the valves before they are installed in the field.

API 6D is widely recognized and adopted as a benchmark in the industry, helping to ensure consistent quality and performance of pipeline valves. Compliance with API 6D is often a requirement in project specifications and regulatory frameworks for pipeline installations.