In brief
Compressor and air receivers are hydrostatically tested at operating pressure at least once a year, unless the standard sets a shorter period, and at the test pressure given in the manufacturing standard at least every 3 years and after every major repair. The safety valve must match the operating pressure or, where no operating pressure has been set, the maximum pressure on the nameplate. Between annual reports, checking the drain, pressure gauge and corrosion is the operator's daily job.
Pressure vessel safety is not just the annual report
Almost every workshop has a compressor with an air receiver next to it, and it is often the least looked-after equipment in the compressor room. Yet the tank is an energy source storing air at high pressure. A shell thinned by corrosion or a safety valve that does not work can lead to a pressure vessel explosion and serious injuries. Pressure vessel safety is therefore not just the inspection report that arrives once a year; the 364 days in between also need a plan.
The basis is Annex III of the Work Equipment Regulation, renewed on 23 December 2025. In Table 1, the maximum period for "compressed air and gas tanks" is 1 year where the standards do not specify a period. The table's footnote defines the scope clearly: mobile or fixed compressor air receivers and all types of vessels containing compressed air, together with their fixed fittings. The general part of Annex III requires equipment to be checked by its operators before each start of work, to be visually inspected for signs such as corrosion, cracks and deformation, and these checks to be recorded.
For the periods for all equipment groups, see our guide to periodic inspection periods for work equipment; this article focuses only on what compressor and air receivers mean in practice on site.
Critical points on the tank
When you look at an air receiver, there are six points you need to check:
| Point | Function | Check on site | Common fault |
|---|---|---|---|
| Safety valve | Releases air if pressure exceeds the set value | Are the seal and label in place, is the outlet open, is it leaking? | Outlet taped or painted over; a valve fitted between the safety valve and the tank |
| Pressure gauge | Shows tank pressure | Is it legible, does the needle return to zero when unpressurised, is operating pressure marked? | Broken glass, stuck needle, unreadable scale |
| Drain valve | Drains condensed water and oil | Is it opened at the frequency in the instructions, does the automatic drain work? | Not opened for weeks, drain outlet blocked |
| Shell | Carries the pressure | Is there rust, blistering, dents, impact damage, cracks in the weld seams? | Advanced corrosion in the lower area in contact with the floor |
| Nameplate | Maximum pressure, volume, year of manufacture, serial number | Is it legible, does it match the records? | Painted over or removed nameplate |
| Connections | Hoses, couplings, pipes | Are there leaks, cracked hoses, unsecured lines? | Hose whipping under pressure, makeshift joints |
Safety valve check
The safety valve is the tank's last safety barrier. In normal operation, the compressor's pressure switch stops the motor; if the switch fails, it is the valve that prevents pressure rising to a dangerous level. So do not treat one as a substitute for the other.
Under Annex III item 2.1.1.1, on pressure equipment with a set operating pressure, safety valves and similar safety devices must match the set operating pressure; on equipment without a set operating pressure, they must match the maximum pressure on the nameplate. On site, this means:
- The valve's set pressure must be known from its label or certificate. If it is not known, this should be queried at the periodic inspection.
- There must be no shut-off valve between the safety valve and the tank that could disable the safety valve.
- The valve outlet must be open and not pointing towards workers; it must not be painted over, taped or blocked with dirt.
- On valves with a test lever, manual testing is carried out at the frequency and by the method in the manufacturer's instructions.
- If the valve is replaced, a certified product with the same set pressure is used; the adjusting screw is not tampered with to "get a bit more pressure".
Pressure gauge and operating pressure marking
Annex III item 2.1.4 sets an important rule: on pressure vessels used below the maximum pressure stated on the manufacturer's nameplate, the operating pressure is marked so that it is visible. If a pressure above the operating pressure is to be applied, the vessel may not be used until it has been tested for that pressure.
In practice, this marking is usually a value written on the tank and a clear line on the gauge dial showing the operating pressure. The operator must be able to tell "normal" from "too high" at a glance. The gauge itself must also be checked: pressure cannot be monitored with a gauge that does not show zero on an unpressurised tank or has broken glass.
Draining and corrosion checks
Moisture in the air compressed by the compressor condenses as it cools in the tank, and water collects at the bottom. This water, together with oil, corrodes the tank from the inside. Corrosion that starts on the inside cannot be seen from outside; the shell thins without anyone noticing.
- Draining frequency: follow the frequency in the manufacturer's instructions. In humid environments or with heavy use, the need increases; if the instructions give no frequency, address daily draining in the risk assessment.
- Automatic drain: if there is an automatic drain valve, check regularly that it works; a blocked automatic drain is more dangerous than no drain at all because it creates a false sense of security.
- External corrosion: tank feet, the lower area in contact with the floor, weld seams and paint blisters are monitored carefully. Raising the tank off a damp floor and keeping the surrounding area dry extends its life.
- No repairs: welding brackets onto the shell afterwards, drilling holes or straightening dents changes the tank's design. Annex III makes a hydrostatic test at test pressure mandatory after every major maintenance and repair.
Annual inspection and test pressure every 3 years: what it means on site
Annex III item 2.1.1 requires, unless the standards state otherwise, that pressure vessels are examined at every periodic inspection and that tests are applied as follows:
| Test | When? | At what pressure? |
|---|---|---|
| Hydrostatic test | At least once a year, at every periodic inspection | At operating pressure if one has been set; otherwise at maximum pressure |
| Hydrostatic test at test pressure | At least every 3 years and after every major maintenance and repair | At the hydrostatic test pressure in the manufacturing standard; if the standard gives no value, at 1.5 times the maximum pressure |
The practical consequences of this table on site are:
- The hydrostatic test is done with liquid. The regulation states that the test may be carried out with water or with liquids deemed suitable in the standard or the manufacturer's instructions. The tank is emptied, filled with liquid, tested and dried. Plan in advance how you will meet your compressed air needs during this time.
- If the test cannot be done, the reason is recorded. If a hydrostatic test cannot be carried out because of the nature of the equipment or the essential conditions of the process, non-destructive testing methods specified in the standard or the manufacturer's instructions may be applied and the reason written in the report. Annex III is clear: being unable to stop the equipment or process is not a valid reason. Non-destructive testing is carried out by personnel certified to at least level 2 under TS EN ISO 9712.
- Who carries out the inspection? Periodic inspections of pressure vessels are carried out by mechanical, metallurgical and materials, mechatronics, chemical, manufacturing and aeronautical engineers, and by technical teachers with a mechanical or metal training background, and mechanical technicians and senior technicians. The person carrying out the inspection must be registered on EKIPNET (the Ministry's online register of periodic inspectors), and the contract must be made through ISG-KATİP (the Ministry's online OHS registration system) at least 1 day before the inspection; for how this works, see our article on ISG-KATİP contract approval.
Equipment found to have a serious defect in the report may not be operated until the defect has been remedied. Annex III also states that the inspection frequency may be increased depending on environmental conditions, frequency of use, the age of the equipment and the results of previous inspections; for a humid, old and heavily used tank, the annual period is an upper limit, not a target.
Compressor room and use of compressed air
The tank alone is not the only risk; its surroundings must also be assessed. The compressor's belt and pulley drive should be enclosed with a fixed guard; on this topic, see our article on machine guards. The compressor room should be ventilated, oil leaks cleaned up and the room not used as a store. Because of compressors' high noise levels, time spent working in the room and hearing protection are planned according to the action values in the noise regulation. If compressed air is used to clean dust and swarf, the air must never be directed at the body or clothing; where possible, cleaning methods using suction should be preferred.
Maintenance and repair records are kept for the service life of the equipment, and periodic inspection reports for as long as the equipment is in use. The 2026 base administrative fine for not having the required inspections and measurements carried out is 33,326 TL; the amounts are on the OHS administrative fines page. You can track the inspection dates of tanks and other equipment with the OHS calendar.
In businesses in Bursa and the surrounding provinces, especially in metal and machinery, we draw up an inventory of compressor tanks, plan inspections with authorised persons registered on EKIPNET and follow up defects in the reports as part of our periodic inspection service.
Frequently Asked Questions
How often is a compressor tank periodically inspected?
At least once a year, unless the relevant standard sets a shorter period. Annex III explicitly includes mobile or fixed compressor air receivers in this scope. If conditions of use are severe, the inspection frequency can be increased.
How is the air receiver test pressure determined?
At the annual inspection, the test is carried out at operating pressure, or at maximum pressure if no operating pressure has been set. At least every three years and after a major repair, the test pressure in the manufacturing standard is applied, or 1.5 times the maximum pressure on the nameplate if the standard gives no value.
Can we change the safety valve setting ourselves?
You should not. The valve must match the operating pressure or the maximum pressure on the nameplate; raising its setting leaves the tank unprotected. A leaking or suspect valve should be replaced by an authorised service technician with a certified product of the same set value.
Is the tank of a mobile compressor also subject to inspection?
Yes. The footnote to Annex III Table 1 states that the compressed air and gas tanks row covers mobile or fixed compressor air receivers and all types of vessels containing compressed air.
Equipment inventory and an inspection calendar under the new Annex III, with inspections carried out through our solution partners, plus report and defect follow-up.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.