Maintenance & Reliability · SOP
Compressor Air Receiver Tank Internal Inspection
This procedure covers the complete internal inspection of a stationary compressed air receiver tank, including isolation, confined-space entry (if applicable), visual inspection, ultrasonic thickness measurement, and documentation. Required for compliance with jurisdictional pressure vessel safety regulations.
Estimated Time
90 min
Difficulty
Advanced
Regulation
ASME Section VIII
Version
1.0
Purpose
The purpose of this procedure is to ensure the structural integrity of the compressed air receiver tank by performing a systematic internal inspection. This inspection identifies corrosion, pitting, cracking, or other degradation that could lead to catastrophic failure. Adherence to this SOP ensures compliance with applicable pressure vessel codes and maintains a safe working environment.
Scope
This SOP applies to all stationary compressors with air receiver tanks that require periodic internal inspection per the facility's preventive maintenance program or regulatory requirements (e.g., WorkSafeBC, Technical Standards & Safety Authority). It covers tanks with manhole/handhole access; tanks without access ports must be inspected using robotic crawlers or alternative NDE methods as per a separate procedure. This SOP does not cover external inspection, relief-valve testing, or hydrostatic testing.
Safety Precautions
- Lock out and tag out the compressor electrical disconnect and close the isolation valve before any work. Verify zero energy with a gauge and a bleed-down.
- Wear full PPE: hard hat, safety glasses, cut-resistant gloves, steel-toe boots. Use a full-body harness and lifeline if entry is required. Have a standby attendant trained in confined-space rescue.
- The receiver tank may be classified as a confined space. Perform a hazard assessment, obtain a confined-space entry permit, and maintain continuous gas monitoring for O₂ (19.5–23.5%), LEL <10%, and CO <35 ppm.
- Ventilate the tank interior with a positive-pressure blower rated for explosive atmospheres for at least 10 minutes before entry and continuously during work. Use only explosion-proof lighting.
Required Tools & Materials
- Lockout/tagout kit (padlocks, tags, group lockbox)
- Explosion-proof flashlight or drop light (24 V max.)
- Ultrasonic thickness gauge with calibration block
- Torque wrench (calibrated) and appropriate sockets
- Replacement gaskets (manhole/handhole)
- Confined-space entry kit: harness, lifeline, tripod or winch, gas monitor (O₂, LEL, CO)
- Positive-pressure blower/ventilator, explosion-proof fan
- Personal protective equipment (hard hat, safety glasses, cut-resistant gloves, steel-toe boots, N95 or supplied-air respirator)
- Hand tools: wrenches, screwdrivers, non-sparking scraper
- Lint-free cloths, industrial vacuum, silicone-based lubricant (for gasket installation)
- Digital camera for documentation, inspection report forms
Procedure: Step-by-Step
1
Obtain confined-space permit (if required): Prior to any work, check if the tank meets confined-space criteria (limited entry/exit, hazardous atmosphere). If yes, complete a hazard assessment, designate an attendant, and secure a written permit.
2
Isolate and de-energize: Lock out the compressor electrical disconnect using a group LOTO procedure. Close and lock the discharge valve. Bleed off all pressure through the manual drain valve. Confirm zero pressure on the gauge (if gauge reads zero, crack a vent valve to verify no flow).
3
Drain condensate and open access ports: Open the bottom drain valve fully to remove any condensate or oil. Remove bolts from manhole cover or handhole flanges using a cross-pattern. Leave two bolts loosely in place until you are sure no residual pressure exists. Carefully remove cover.
4
Ventilate and monitor atmosphere: Position a positive-pressure blower at the manhole opening, directed into the tank, and run for at least 10 minutes. Use an explosion-proof fan if needed. Test interior air with a calibrated gas monitor: O₂ 19.5–23.5%, LEL <10%, CO <35 ppm. Record readings on the permit.
5
Don PPE and prepare for entry: Put on full PPE including harness and lifeline. Attach lifeline to a tripod or winch above the manhole. Ensure the attendant is stationed outside with continuous visual or voice contact. Have an emergency rescue plan in place.
6
Perform visual inspection: Enter the tank (or use a mirror on a stick for smaller openings). Use an explosion-proof light to systematically scan the interior shell, head, and weld seams. Look for: corrosion, deep pitting, cracks, blistering, oil or scale deposits, and any signs of mechanical damage. Photograph all suspect areas.
7
Ultrasonic thickness (UT) measurements: Use a calibrated UT gauge with a delay-line transducer. Measure wall thickness at a minimum of five locations per shell course: bottom third, middle, top third, and near each longitudinal weld seam. Also measure at the bottom head (most susceptible to corrosion). Record each reading in millimetres. Compare to the required minimum wall thickness per the manufacturer’s data sheet or ASME Section VIII Div.1.
8
Clean interior (if UT is acceptable): Using a vacuum and non-sparking scraper, remove any loose debris, rust flakes, or oil residue. Wipe surfaces with lint-free cloths. Do NOT use solvents unless specifically approved and ventilation is increased. If UT readings indicate wall loss beyond the minimum, do not clean; flag the tank for engineering evaluation and possible decommissioning.
9
Replace gaskets and close ports: Remove old gasket material. Apply a fresh gasket (full-face type) compatible with compressed air service. Lubricate bolts with anti-seize compound. Install cover bolts in a cross-pattern and tighten to the manufacturer’s torque specification in two passes (50% then 100% torque). Mark each bolt with a torque stripe.
10
Restore service and document: Close all drain valves. Remove LOTO tags and locks per the facility's procedure. Restore power to the compressor. Slowly pressurize the system to working pressure (no faster than 50 psi/min). Apply a soap-and-water solution to all gasketed joints to check for leaks. Document all inspection findings, UT readings, photos, and any corrective actions in the maintenance log or CMMS. Attach the completed confined-space permit and UT report to the record.