Platform Mounted Reciprocating Compressors, Fatigue Consideration

Installations where a reciprocating compressor is driven by an electric motor over 2HP and is directly mounted on the platform supported by the tank must meet the requirements of ASME Code Section VIII, Division I, Paragraph UG-22. In this regard, Hanson provides the required installation data for the assembled unit. Specifically it states whether the particular compressor - motor - air receiver combination is satisfactory when bolted or non-bolted to the floor and whether it requires soft or hard mounting to be acceptable. This information is applicable to both horizontal the vertical platform mounted units, but is unavailable for gasoline or diesel engine drives.

Pressure Relief Valves

Each air tank shall be protected by 1 or more safety valves and other indicating and controlling devices that will insure safe operation of the tank. If the tank has a volumetric capacity in excess of 2,000 gallons, it shall be fitted with at least 2 safety valves, the smallest of which shall have a relieving capacity of at least 50 percent of the relieving capacity of the largest valve. These appliances shall be constructed, located, and installed so that they cannot be readily rendered inoperative. Safety valves shall be of the direct spring-loaded type, and for pressures of 2,000 psi or less shall be equipped with a substantial lifting device so that the disc can be easily lifted from its seat not less than 1/8 the diameter of the seat when the pressure in the tank is 75 percent of that at which the safety valve is set to open. For pressures in excess of 2,000 psi, the lifting device may be omitted providing the valve is removed for testing at least once each year and a record is kept of this test and made available to the qualified inspector. For pressures exceeding 2,000 psi acceptable rupture discs may be used in lieu of spring-loaded safety valves. All safety valves shall be ASME stamped and rated for air pressure service. The safety valves and rupture discs shall be set to open at not more than the allowable working pressure of the air tank, and the relieving capacity shall be sufficient to prevent a rise of pressure in the tank of more than 10 percent above the allowable working pressure when all connected compressors are operating with all unloading devices rendered inoperative. The opening or connection between the tank safety valves shall have a cross-sectional area at least equal to the combined areas of all attached safety valve inlets.

No valve of any description shall be placed between the required safety valve or rupture discs and the air tank.

All safety valves shall be tested frequently and at regular intervals to determine whether they are in good operating condition. It is recommended that safety valves up to and including 200 psi setting shell be tested at least monthly. Discharge pipes from safety valves and rupture discs installed on air tanks shall have a cross-sectional area at least equal to the combined outlet areas of all valves discharging into them, and shall be designed and installed so that there will be no interference with the proper operation or discharge capacity of the safety valve or rupture disc. No valve of any description shall be permitted in these discharge pipes. All discharge pipes shall be fitted with open drains which will prevent the accumulation of liquid above the safety valve seat or rupture disc. Discharge pipes shall be installed and supported in a manner that will prevent undue stresses on the safety valve or rupture disc. The discharge from all safety valves and rupture discs shall be led to a safe place of discharge.

Pressure Gauges

Each air receiver shall be equipped with a suitable pressure-indicating gauge with the dial graduated to not less than 1.2 times the pressure at which the safety relief valve is set to function.

Drain Connection

Each receiver shall be equipped with a manually operated, valve drain located at the lowest point in the receiver where water can collect. Even automatic drains should be equipped with a manually operated bypass. It is recommended that the receiver be drained once each day of operation.

Piping

Piping and components attached to the receiver should be installed with adequate support and provisions for expansion and vibration dampening to prevent excessive loading on the receiver. This should be done utilizing flexible connections at the vessel inlet and outlet(s). It is also recommended that excessively long runs of piping, if used, should be adequately supported and provided with shock isolators to minimize fatigue loads from being transmitted back to the receiver.

Piping from the receiver to the first shut off valve must be rated extra-heavy. Plastic piping or tubing must never be used in any air distribution system.

Inspection

Air receivers shall be so installed that all drains, handholes, inspection plugs and manholes therein be easily accessible. Receivers should be installed with sufficient clearance to permit a complete external inspection and in such a manner to avoid corrosion of external surfaces. Under no circumstances shall the receiver be buried underground or located in an inaccessible place or location.

Mounting of the horizontal and vertical tanks of all sizes require installations that are in accordance with approved National Standards. This could include foundations and bolting to meet wind or seismic loading. Detailed designs for mounting are available to meet all design requirements.

In most jurisdictions, a permit to operate an air receiver is required when located in public places and places for employment. Once granted, the receiver is re-inspected at intervals in accordance with the local laws. This may be yearly or every three years but should not be more than every five years. These inspections are performed by the local jurisdiction or insurance company representative, who are commissioned by the National Board of Boiler and Pressure Vessel Inspectors. Regardless of jurisdictions, it is the responsibility of the user/owner of the air tank to assure that the vessel has not deteriorated by erosion or corrosion.