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Air Receivers

Print Date : 9/30/2011 1:48:34 AM

Description and OverviewAn air receiver is probably the most common type of unfired pressure vessel. However, due tominimum size inspection thresholds employed by the vast majority of jurisdictions, many of thesmaller air receivers will not qualify for a mandatory inservice inspection. The typical inspectionthreshold sizes referenced in jurisdictional regulations are 5 cubic feet or 15 cubic feet involume as long as the maximum allowable working pressure (MAWP) does not exceed 250 psi,

or 1-½ cubic feet in volume as long as the MAWP does not exceed 600 psi. The inspector mustreview the jurisdiction's inspection requirements to ensure compliance with the appropriate sizeand pressure limitations.

Air receivers are typically constructed in accordance with ASME Section VIII, Div. 1, andstamped with either the ASME "U" or "UM" symbol. Manufacturers who specialize in air receivers will construct a large number of these vessels in an assembly line process. TheManufacturer's Data Report , for "U" stamped vessels, and the Manufacturer's Certificate of Compliance , for "UM" stamped vessels, may include multiple vessels. This practice isdescribed in ASME Section VIII, Div. 1, paragraph UG-120(a).

While most air receivers are of simple design consisting of a shell and two dished heads, some

are designed to incorporate a filter or separator element within the vessel. These vessels maybe "T" shaped with one bolted flat head which provides access to the filter or separator element. These uniquely shaped vessels are commonly found in use with large industrial air compressors.

Air receivers will be installed in any facility requiring a reservoir of compressed air. Compressedair uses include:

Tire Inflation■

Air-Powered Tools■

Pneumatic Cylinders or Pistons■

Sand- or Shot-Blasting■

Painting■

Cleaning■

Air Motors■

Conveying Systems■

Pneumatic Controls■

Breathing Air ■

The design of a compressed air system is dictated in part by the pressure, volume, and air quality (including cleanliness and dryness) needed in any given industry or process. The size of the air receiver in the system is normally based on the volume of air produced by the

of 4The National Board of Boiler and Pressure Vessel Inspectors

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thickness necessary for the MAWP stamped on the vessel. Under those circumstances, theMAWP can be decreased to a point that is supported by the remaining wall thickness, but inmost cases the vessel is removed from service until it is repaired or replaced.

Vibration caused by an integrally mounted compressor/motor unit can cause cracking in thewelds attaching the compressor/motor mount to the air receiver or in the welds attaching thebase to the bottom of the air receiver. If they occur, the cracks will often "run" or propagate into

the vessel material. Vibration damage can also occur where rigid piping is connected to the air receiver.

External impact damage can be caused by vehicles, machinery, or objects hitting the air receiver. One inspector observed a large dent in an external air receiver mounted on a portableair compressor used in a quarry. He was told it was caused by a limestone boulder which fellon the compressor from an upper rock ledge. Hazards can exist almost anywhere.

Most air receivers will show a minimum design metal temperature (MDMT) of -20°F on thenameplate. This should be acceptable under most conditions. However, if the air receiver isinstalled outside or in an unheated structure in very cold climates, it could be susceptible tobrittle fracture.

InspectionUpon entering the area where the air receiver is operating, the inspector should perform ageneral assessment of the air receiver, piping, and associated systems. The inspector shouldthen:

review the current operating certificate (if one was issued in the past) and compare theinformation to the associated air receiver and its nameplate;

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compare the pressure relief device data (set pressure and relieving capacity) with the air receiver nameplate and compressor output data to ensure the pressure relief device isadequate for this installation;

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inspect the pressure relief device operation as described in the National Board Inspector

Guide for Pressure Relief Devices ;

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check all support and mounting bracket attachment welds and the affected vessel wallsfor evidence of cracking;

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check for external damage such as dents or gouges;■

ask the owner or owner's representative to verify the operation of the automaticcondensate drain if applicable, or open the manual drain valve;

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check connected piping to ensure it is properly supported and not imparting excessiveloadings on the air receiver.

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The inspector should perform an internal inspection of the air receiver as required by the jurisdiction. Some air receivers have dedicated inspection openings while others (especiallysmaller ones) use the inspection openings for the attachment of piping, instruments or similar

attachments as allowed by ASME Section VIII, Div. 1, paragraph UG-46(f)(7). If an internalinspection is impractical, the jurisdiction may accept thickness readings obtained with anultrasonic tester compared with original thickness values. The original thickness values can befound on the Manufacturer's Data Report or Manufacturer's Certificate of Compliance . Althoughthe practice is not required by ASME Code, some air receiver manufacturers include the shelland head thicknesses on the nameplate.

Miscellaneous InformationAdditional information to aid inspectors of air receivers can be found in the followingpublications and sources:


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National Board Inspection Code ■

ASME Section VIII, Div. 1■

Manufacturer's Installation, Operation, and Maintenance Documentation■

Jurisdictional Laws, Rules, and Directives■


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