Air receivers on compressors and drill rigs, hydraulic accumulators, gas storage and process vessels are all pressure equipment. AS/NZS 3788 sets out the in-service inspection they require, at intervals determined by the vessel's hazard level under AS 4343, and the WHS Regulations require design registration — and item registration for hazard levels A, B and C — before they are used.
We carry out external and internal in-service inspections of pressure vessels and associated piping to AS/NZS 3788, including thickness surveys, safety valve verification and registration checks, and report the next inspection due date for the plant register.
Inspection checklist areas
- Documentation and registration
- Design registration number, item registration where required, nameplate data (design pressure, temperature, capacity, standard of manufacture), hazard level to AS 4343, previous inspection reports.
- External inspection
- Shell and head corrosion, dents and gouges, nozzle and support welds, saddle and foundation condition, insulation damage, drain function, evidence of leakage.
- Internal inspection
- Internal corrosion, pitting and scaling at the waterline and floor, weld condition, nozzle internals, subject to confined space entry controls.
- Thickness survey
- UT thickness measurement at a defined grid and at areas of visible corrosion, compared with the minimum required thickness and corrosion allowance from the design.
- Safety and control devices
- Pressure relief valve set pressure, capacity and test date, pressure gauge accuracy and range, drain valves, isolation valves, high-pressure cut-outs.
- Piping and fittings
- Associated piping supports, flexible connections, corrosion under insulation, hose assemblies on mobile equipment.
Known failure modes
Internal corrosion and wall thinning
Condensate corrosion at the floor of air receivers, reducing wall thickness below the required minimum.
Rupture from over-pressure
Relief valve seized, isolated or incorrectly set, allowing pressure to exceed design.
Weld and nozzle cracking
Fatigue cracking at nozzle-to-shell welds and support attachments under pressure cycling and vibration on mobile equipment.
External corrosion under insulation or at supports
Hidden wall loss where water is trapped against the shell.
Unregistered or undocumented vessels
Vessels in service without design registration or known design data, making assessment of fitness impossible without engineering review.
Applicable standards and regulations
| Reference | Title | Relevance |
|---|---|---|
| AS/NZS 3788 | Pressure equipment — In-service inspection | Inspection scope, intervals, competency and reporting for pressure equipment in service. |
| AS 4343 | Pressure equipment — Hazard levels | Determines hazard level (A to E) which sets registration and inspection requirements. |
| AS 1210 | Pressure vessels | Design and construction basis against which condition and minimum thickness are assessed. |
| AS 3873 | Pressure equipment — Operation and maintenance | Owner obligations for operation, maintenance and record keeping. |
| AS 1271 | Safety valves, other valves, liquid level gauges, and other fittings for boilers and unfired pressure vessels | Requirements for pressure relief devices and fittings. |
| Model WHS Regulations, Schedule 5 | Plant requiring design and item registration | Pressure vessels with hazard level A, B, C or D require design registration; A, B and C also require item registration. |
Inspection intervals
- Intervals per AS/NZS 3788
- Set by vessel class, service and hazard level. For a typical compressed-air receiver the standard's tables provide an external inspection every 2 years and an internal inspection every 4 years, with the competent person able to vary intervals based on condition and history.
- Pressure relief valves
- Tested or replaced at intervals set under AS/NZS 3788 and the manufacturer, and verified at each vessel inspection.
When to inspect
- Inspection due date from the previous AS/NZS 3788 report
- Vessel arriving on site with a compressor, drill rig or plant package
- Evidence of leakage, corrosion or relief valve lifting
- After repair, modification or relocation of the vessel
- Audit finding of unregistered pressure equipment
Frequently asked questions
How often do air receivers need inspecting?
AS/NZS 3788 sets intervals by vessel class and hazard level. For common compressed-air receivers the tables provide an external inspection every 2 years and an internal inspection every 4 years, subject to adjustment by the competent person based on condition and history. The report states the next due dates.
Do all pressure vessels require registration?
Under the model WHS Regulations, pressure vessels with a hazard level of A, B, C or D under AS 4343 require design registration, and those at hazard level A, B or C also require item registration. Hazard level E vessels are exempt from registration but still require in-service inspection under AS/NZS 3788.
What if the vessel has no nameplate or design data?
Without design pressure, material and thickness data the vessel's fitness cannot be verified by inspection alone. We report it as undocumented and refer it for engineering assessment, which may include material identification and calculation to AS 1210 or replacement.
Is internal inspection always required?
Internal inspection is required at the intervals in AS/NZS 3788 unless the vessel is exempt or an alternative such as UT thickness survey is accepted by the competent person for that vessel class. Internal entry is carried out under confined space controls.