PSSR Written Scheme of Examination: What to Get from Your Vendor

Under the Pressure Systems Safety Regulations 2000 (PSSR), the user of an installed pressure system must not run it until it has safe operating limits and, for most systems, a written scheme of examination that a competent person has drawn up or certified as suitable [1]. The scheme names the vessels, pipework and protective devices to be examined, says how and how often, and, where appropriate, calls for an examination before first use [1, 3]. The competent person sets the intervals; the law does not fix them [2, 3].

A competent person cannot write a good scheme without the vendor's design data, so require it in the RFQ and purchase order, and have it before the equipment arrives.

Why this matters now

HSE says qualifying equipment, new or otherwise, needs a scheme in place before use, and the regulations require an examination before first use wherever the scheme provides for one [1, 4].

In 2024 EEMUA, SAFed (the Safety Assessment Federation) and the Pressure Equipment Consultation Forum, with technical advice from HSE, published EEMUA 248, a free guide to the information a competent person needs to draw up a scheme [7].

What PSSR covers and who holds the duties

PSSR applies in Great Britain to pressure systems used at work [1]. A pressure system is one or more rigid pressure vessels with their pipework and protective devices, or a pipeline, containing or liable to contain a relevant fluid. That means steam at any pressure, or a gas above 0.5 bar above atmospheric pressure. A liquid held above 0.5 bar counts if its vapour pressure would exceed 0.5 bar above atmospheric at its actual temperature or 17.5 °C [1]. HSE gives pressurised hot water above 110 °C as an example and excludes hydraulic oils [4, 8], though L122, HSE's Approved Code of Practice, lists a gas loaded hydraulic accumulator among items likely to need a scheme [2].

In a system without steam where every vessel's pressure times volume is below 250 bar litres, the regulations on the scheme, examinations and records do not apply; steam systems get no such exception. Safe operating limits, operating instructions and maintenance duties still apply to those small systems [1]. And for equipment placed on the market under the Pressure Equipment (Safety) Regulations 2016 (PE(S)R), the PSSR design and supplier information duties give way to PE(S)R's own [1].

An in house competent person should be independent of operations, with authority to stop the equipment [4]. UKAS accreditation to ISO/IEC 17020 is voluntary, but L122 recommends it for bodies working on major systems [2]. If you lease or hire an installed system, the supplier can accept the scheme duties in writing [4].

Northern Ireland has its own Pressure Systems Safety Regulations (Northern Ireland) 2004, with the same structure, including a regulation on the written scheme [9]. This is general information, not legal advice.

What the scheme contains, and who sets the intervals

The user decides which parts of the system the scheme covers. The competent person specifies the nature and frequency of examination and any special preparation [2]. HSE's leaflet sums up the scope rule as "one system, one scheme" [3].

A scheme normally sets out [2, 3]:

• the plant, and the parts to be examined
• the nature of each examination, including testing of protective devices
• preparatory work for safe examination
• any examination before first use
• the maximum interval between examinations
• critical parts to examine after repair or modification
• the certifying competent person's name and the date

Protective devices should be examined at least as often as the plant they protect [2].

L122 asks the competent person to use judgement and experience, weighing history, condition, operating conditions, fluid quality, maintenance and any on stream monitoring [2]. Earlier legislation, it notes, used fixed maxima: usually 14 months for steam plant, 26 to 38 months for steam receivers linked to it, and 24 to 48 months for air receivers, or 72 months where corrosion was minimal and standards high. A competent person may use these as a guide, not as legal limits [2].

After each examination the competent person sends a signed, dated report within 28 days (sooner if it sets an earlier repair deadline), with the date after which the system may not run without another examination [1]. If that causes no danger, the date can be postponed once, by written agreement with the competent person and prior written notice to the enforcing authority [1].

What to require from the vendor at purchase

PE(S)R requires instructions covering mounting, putting into service, use and maintenance, including checks by the user, with technical documents, drawings and diagrams where appropriate [5]. It also requires marking that includes the allowable limits and, where relevant, the volume, test pressure and date, and safety device set pressure [5]. PSSR then makes the user keep those instructions alongside the examination reports [1]. These rules apply to equipment in the PE(S)R hazard categories; items made to sound engineering practice carry no UKCA or CE mark and need only adequate instructions [6]. PE(S)R also lets the manufacturer keep the technical file, including calculations, rather than hand it over [6], so name the design data you need in the order.

L122 says the manufacturer of a standard production item should assess its safe operating limits and pass them on; for a user specified design, that falls to the user. The table follows L122's design information list [2].

Ask too for the pressure test certificate and its basis (see hydrostatic test pressure), and for a vessel built to ASME VIII, how PE(S)R conformity was shown (see ASME VIII vs PD 5500 vs EN 13445).

Practical example

Take an illustrative reactor skid for a site in England, using the maximum allowable pressure in bar gauge (an assumption; confirm the basis with your competent person).

A 20 litre air receiver would be 200 bar litres; as the only vessel on its own air system, it would need no scheme, though safe operating limits and maintenance would still apply [1]. The reactor's 8,000 bar litres is far below the 100,000 bar litres L122 uses as one marker of a major chemical reaction system [2].

Illustrative timing: data pack due at week 12, delivery at week 16, first use at week 20, and an assumed 4 weeks for the competent person to certify the scheme from a complete pack. A pack at week 12 gives a scheme at week 16, leaving 4 weeks for installation and the examination before first use. A pack that arrives with the skid gives a scheme at week 20, with no time for that examination.

Make the data pack part of the order

Scheme data is cheap to request and slow to chase. ChemCapital sends one structured RFQ to all your suppliers at once, so every bidder sees the same data pack requirement and you compare their replies side by side. After award, suppliers post milestone updates against the order, and a timestamped audit trail records every interaction, revision and decision.

Ready to get the scheme data with the equipment, not after it? Start free with ChemCapital.