Several vendors specialize in building wellhead control panels. In order to be competitive, they will offer to supply the minimum number and lowest quality of logic and panel components.
To get a panel that is reliable and maintainable, a drawing should be prepared that shows in general terms such things as the following.
• Available space that the panel can occupy or the maximum acceptable panel dimensions
• Accessibility to the panel for maintenance and the location of doors and bulkheads
• General layout of the controls showing the wellhead control groupings, the location of subsurface controls for each well in relation to the surface controls, and the location of the hydraulic control unit and manual pump override
• The minimum and maximum height of the controls from grade and how the panel is to be mounted
• The amount of space required for expansion
• Nameplate engraving details including the lines of text, the size of letters and nameplate, and color scheme, if any
• Distances from the field devices to the panel
• Indication requirements for such things as valve status and bypass switches
• Bypass switch and test valve requirements
• First out indication requirements for shutdown sensors
The drawing or an attached specification should include a list of the components and the acceptable manufacturers.
To ensure quality and reliability, it is often necessary to include model numbers to avoid the problem when a vendor supplies the least expensive option. Model numbers also help in bid evaluation, during inspection of the finished panels, and to maintain standardized spare parts.
Vendors should be allowed to offer reasonable substitutions in order to produce the lowest cost panel by avoiding unusual construction requirements.