How should I be doing risk assessments in facilities like tank farms, compressor stations, etc?

Exactly the same way as for components on the ROW. You don’t want or need multiple risk assessment approaches. A good risk assessment methodology works equally efficiently on any component or any collection of components. 
The challenge with facilities will be in segmentation. The more robust assessments will examine very small sub-components (eg, the casing of the pump distinct from inlet and discharge flanges; tank bottom distinct from tank sides and top; etc) while a more general assessment might examine collections (eg, tank battery, manifold circuit, etc). 

The latter is a compromise solution that results in reduced accuracy but is often a step in the process towards a robust risk assessment.