EN
Air Tank
Periodic inspection of compressor air receivers: internal-external examination, ultrasonic thickness measurement and safety valve tests, with signed reports.
Air tank periodic inspection is the regular examination and testing, by authorised engineers, of the cylindrical pressure vessels that store compressed air downstream of piston or screw compressors and feed the dryer and distribution network. Body integrity, corrosion state and safety devices are assessed; the aim is to detect wall thinning before it can exceed the working pressure — an event with high stored energy in these vessels.
What Is an Air Receiver and Why Is It Critical?
An air receiver is a vertical or horizontal pressure vessel that collects the compressed air produced by the compressor, balances pulsation, separates condensed water and covers sudden demand peaks. A rupture in an air receiver releases free energy comparable to a steam boiler of the same volume, because compressed air expands and creates a shock wave. Condensate on the inner surface deepens corrosion at the bottom when uncontrolled, reducing plate thickness. Key inspected components:
- Shell, bottom head (dished end) and weld seams
- Safety valve, pressure gauge and pressure switch
- Automatic/positioned condensate drain valve
- Compressor-dryer connections, supports and anchors
Periodic Inspection Items
- External examination: Check of rot under paint, deformation, weld cracks and support conditions.
- Internal examination: Boroscope camera survey of vessels that cannot be entered; search for scaling and deep pitting corrosion in the bottom zone.
- Ultrasonic thickness measurement: Measurement at pre-mapped points, comparison against the minimum design thickness and remaining life calculation from the corrosion rate.
- Hydrostatic pressure test: Strength verification at 1.5 times the working pressure at the long-term interval defined by manufacturer data and standard.
- Safety devices: Set-pressure test and free-operation check of the safety valve; gauge calibration verification.
Legislation and Standards
Inspection is performed under Law No. 6331 and the Work Equipment Regulation; unless otherwise foreseen, pressure vessels are controlled at least once a year. The technical basis is the TS EN 13445 series and the equivalent ASME BPVC Section VIII, with the 2014/68/EU (PED) governing equipment conformity. Compressor safety equipment (high pressure switch, cooling protection) is evaluated under machine safety on the compressed air line.
Risks and Operator Recommendations
Neglected draining stands at the centre of almost every air receiver incident: where the automatic trap fails or never existed, condensate accumulates, lowering capacity and accelerating bottom corrosion. The trap function must be tested at every inspection, and the mud layer formed by evaporation must be cleaned in freeze-free environments. On tanks with damaged paint or standing water at the foot, bottom corrosion advances invisibly — external suspicion must be confirmed by internal measurement. A safety valve whose set point has been tampered with allows exceeding design limits; the valve setting is verified against the nameplate pressure. Increasing thickness measurement frequency and keeping results as trends is recommended for aged receivers.
Outcome
At the end of the examination, a signed report containing the thickness map, findings and compliance assessment is delivered. Air receiver inspections are within our Periodic Inspection of Pressure Vessels group. For investment and installation works on the compressor line, see our Hot Oil, Water and Steam Installations service and contact us.
FAQ on Air Tank Inspection
The air receiver stores compressed air as a closed steel volume; high pressure energy is parked in the shell continuously. Thin corrosion, pit corrosion and old weld repairs are where failure starts: a pressure vessel burst is a rare but very lethal fault producing fragment throw and shock wave. Internal moisture-condensate accumulation advancing corrosion silently from the inside surface is the root driver.
Under the Work Equipment Regulation pressure vessel inspection cannot exceed one year; the hydrostatic proof runs at 1,5 times working pressure (five-yearly cycle per code practice). Safety valve set pressure and gauge accuracy are tried at every control. On closed compressor line stations, tank pressure-duty conditions, temperature and automation interlocks are tracked separately per manufacturer and TS EN 13445 approach.
External shell-seam-weld zone corrosion scanning under paint, thickness measurement (UT) where needed; internal cleaning-condensate sludge and rust debris control, bottom drain valve function-automatic relief verification, safety valve-check valve-gauge and pressure switch calibration, foot-support-bonding-corrosion and vibration control, flange-gasket leak scanning, nameplate-data label (pressure-temperature-volume) comparison with the technical file, earthing-bonding.
Condensate relief is the most critical simple precaution: manual drain every shift or automatic drain checked daily, no blocked bottom valve left — this is the internal corrosion rate. Under-ink corrosion scanning is tightened in humid-hot climates and outdoors; winter freeze protection on water-cooled lines. The safety valve outlet is never closed-locked; the yearly engineer control, five-yearly pressure proof plan and records (OHS file) are the mandatory calendar.