I'm looking for a 3D model of a wellhead, These are used in the petroleum/oil fields.
One of the manufactures is FMC Technologies.
Have you tried contacting the manufacturers of the components involved, to ask if they could supply models?
I think that your chance of finding a wellhead assembly that would fit your requirements in a prepackaged SW or IGES or STEP file are very slim. But you can create the wellhead as an assembly of parts that may exist as 3D models. Of course, you will have to create some "connector parts" to represent the necessary assembly.
The only important dimensions are the pipe centerline distances from FMC which can be incorporated as a top down design. In fact, the wellhead can be represented as only a "box" with axies for the pipe connections and CP's if you use routing. You can fill in the geometry of the valve bodies later for visual effects.
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