What is the difference between API 6A and API 6D valves?

API 6D and API 6A are both standards used for Valves in the oil and gas industry. API 6D is standard or specification for valves in any pipeline, including rigs, platforms, skids and production plants.

API 6A is standard or specification for valves used in wellhead and Christmas tree equipment. In terms of usage, there are many more pipeline valves used as compared to wellhead valves.

In terms of ease of manufacture, pipeline valves are more easily manufactured as compared to wellhead valves. In...