The short answer
A document drawn up or certified by a competent person setting out which parts of a pressure system are examined, how, at what intervals, and how the system is prepared for safe examination. Under PSSR 2000 you must not operate the system without one — and without having been examined in accordance with it.
Why a scheme rather than a fixed date
Most statutory inspection regimes give you an interval and leave it there. PSSR does something different: it requires a document, tailored to your specific system, that decides what gets examined and how often.
The reason is the failure mode. A pressure vessel does not wear out gracefully and give warning the way a chain or a bearing does. It holds stored energy, and when a corroded shell lets go the result is immediate. A scheme forces someone competent to look at your particular system — its duty, its condition, its environment — and decide what examination it actually needs.
What the scheme has to cover
It must be drawn up or certified as suitable by a competent person, and it must be kept — it is the first document an inspector will ask for, ahead of any examination report.
- □Which parts of the system are included — vessels, pipework, protective devices.
- □The nature of the examination for each part: external, internal, or a specific test.
- □The intervals between examinations for each item.
- □Any measures needed to prepare the system so it can be examined safely.
- □Any special measures for parts that are difficult to access or cannot be examined in the normal way.
Is your system in scope?
The threshold is based on stored energy: pressure in bar multiplied by volume in litres. A system containing relevant fluid above 0.5 bar gauge, where that figure exceeds 250 bar litres, needs a scheme.
| System | Position |
|---|---|
| Compressor with receiver over 250 bar litres | Written scheme required |
| Stored energy below 250 bar litres | Outside PSSR — PUWER still applies |
| Second-hand or relocated vessel | Examine before it is put into use |
How often the examination falls due
The scheme sets it, not a rule of thumb. For a typical workshop air receiver in sound condition the interval commonly lands somewhere between 24 and 26 months. A vessel in a damp or corrosive environment, on a critical duty, or with a history of defects will be examined more often.
What the scheme does not do is drift. An interval of 26 months means 26 months — not "sometime in the third year when we remember", which is how a great many receivers end up five years past examination.
The inherited scheme problem
The most common situation we find is not an absent scheme; it is an inherited one. A vessel came with the building or the business, there is a document in a folder somewhere, nobody has read it, and nobody knows whether it still describes the system as installed today.
A scheme that no longer matches the plant is not compliance. If pipework has been altered, a receiver moved, or a safety valve replaced with a different set pressure, the scheme needs reviewing. We review inherited schemes as part of a first visit and re-issue where necessary, rather than examining against a document that describes something else.
Still not sure?
Describe your equipment and we will tell you what applies