Tips for Designing and Installing Pressure Vessels
- Provide maximum allowable working pressure (MAWP) and minimum design metal temperature (MDMT) ratings to the vessel manufacturer.
- Bear in mind that the ASME code requires consideration of seismic and other dynamic loadings, as do local building and mechanical codes.
- Allow for corrosion and erosion when specifying a vessel.
- Consider using hot-pressed heads and normalized shell material, which can provide increased vessel strength and corrosion resistance.
- Require internal cleanliness, free from foreign matter and scale.
- Specify that the vessel be shipped with a nitrogen charge.
- Order external surfaces sandblasted and coated with rust-preventive primer to extend the vessel's life and reduce corrosion risk.
- Consider radiography, even if not required by code, to verify the vessel's weld quality before installation.
- Specify seamless pipe for vessels 24" OD and smaller.
- Evaluate total relief assembly - nozzle, three-way manifold valve, relief valve and vent system - pressure drop before and after the valve reduces relief capacity and destabilizes relief valves.
- Consult the manufacturer before switching applicable refrigerant or placing the vessel into new service.
When installing pressure vessels, keep the following points in mind:
- Avoid installation stresses such as construction vehicle or tool impact.
- Leave sufficient space around the vesselfor future maintenance work.
- Do not ever weld on a pressure vessel. Even temporary tack-welds void the ASME code compliance stamp.
- Install insulation properly. The life of the vessel depends on the quality of the insulation system.
- Mount the vessel with the nameplate in an accessible location.
Owners, engineers, installers and technicians should be familiar with the operation and function of each vessel relative to its purpose in the system. Technicians working with pressure vessels also must have a working knowledge of refrigeration systems. Be sure to follow facility standard operating procedures and safe work practices when working with pressure vessels.