PED Categories: How to Classify Pressure Equipment Under PER 2016

Under the EU Pressure Equipment Directive 2014/68/EU (PED) and its Great Britain counterpart, the Pressure Equipment (Safety) Regulations 2016 (PER), equipment with a maximum allowable pressure (PS) above 0.5 bar goes into category I, II, III or IV, in ascending level of hazard, or sits below category I under sound engineering practice (SEP) [1, 3, 9]. The manufacturer sets the category from four facts: the type of equipment, whether the fluid counts as a gas or a liquid, its fluid group, and its PS with its volume V (or nominal size DN for piping) [3].

Category I is self declared; categories II to IV need an approved body for UKCA marking or a notified body for CE marking [2, 3, 9].

Why this matters now

The category sets how much third party work, and so cost and lead time, goes into a vessel. From category II, procedures and personnel for permanent joints such as welds must be approved, and the main pressure parts need a certificate of specific product control. From category III, NDT (non destructive testing) staff must be approved by a recognised third party organisation [1].

Regulations in force from 1 October 2024 extended recognition of CE marking in Great Britain indefinitely, so equipment can carry UKCA or CE [3]; the guidance was unchanged on 25 October 2026.

The four inputs that set the category

Equipment type. Vessels, fired or heated equipment making steam or water above 110 °C, and piping each have their own tables. Pressure accessories, operational devices with a pressure bearing housing, use the vessel or piping table, taking the higher result where both V and DN apply [1, 2].

Fluid state. "Gas" includes vapours and any liquid whose vapour pressure at the maximum allowable temperature (TS) is more than 0.5 bar above normal atmospheric pressure (1013 mbar) [1].

Fluid group. Group 1 covers listed hazard classes of the CLP Regulation, such as explosives, flammable gases, flammable liquids in categories 1 and 2, and some oxidising and acute toxicity categories. It also includes any fluid where the maximum allowable temperature TS exceeds its flash point, whatever temperature the fluid normally runs at. Group 2 is everything else, steam included [1, 3].

PS and V, or PS and DN. PS is the maximum pressure, in bar gauge, that the manufacturer specifies for the design. V is the internal volume of a chamber, including nozzles to the first connection or weld [1].

A vessel takes the highest category of its chambers, and a chamber holding several fluids is classified on the fluid needing the highest category [1]. The Commission's PED guidelines count the shell and tube sides of an exchanger as two chambers of one vessel, so a spare bundle cannot be CE marked alone [7]. Safety accessories, such as safety valves and bursting discs, are category IV unless made for specific equipment, when they may take its category [1, 2].

At or below these regulation 6 limits, equipment is SEP [1, 2]:

Above them, the category is read off the Schedule 1B chart of PS against V or DN [2, 3]. Some text rules override it: vessels and piping for unstable gases in category I or II move to III, and group 2 gas piping in category II carrying fluids above 350 °C moves to III [2].

Sound engineering practice and simple pressure vessels

SEP equipment must be designed and made to sound engineering practice with adequate instructions, and must not carry the UK marking unless other legislation requires it [1, 3]. Size matters: Emerson classes a gas regulator series from SEP at DN 25 to category II at DN 100, and category IV with a slam shut device [8].

Many air receivers sit outside the PER. The Simple Pressure Vessels (Safety) Regulations 2016 cover welded, unfired vessels made in series for air or nitrogen, in non alloy quality steel, non alloy aluminium or non age hardening aluminium alloy, with a maximum working pressure up to 30 bar and PS × V up to 10,000 bar·L [6], and the PER exclude them [1]. A stainless steel receiver, or a one off, falls back under the PER.

UKCA, CE and Northern Ireland

In Great Britain, a UK approved body's work leads only to UKCA marking. An EU notified body's work leads to CE marking and can also support UKCA [3]. HSE says new equipment on the GB market must be UKCA or CE marked with instructions in English [5]; SEP items carry no marking [1].

Northern Ireland still applies the Directive under the Windsor Framework. UKCA is not accepted there, so equipment needs CE; where a UK notified body did the assessment, CE must be joined by UKNI, and the equipment cannot then be placed on the EEA market [4].

This is general information, not legal advice. The PER cover placing equipment on the market, not a user assembling equipment on its own site, where the Pressure Systems Safety Regulations 2000 apply instead [5]. For in service duties, see our PSSR written scheme of examination guide.

What to ask the vendor to state

The nameplate need not show the category, since Schedule 2's marking list omits it [1]. Ask each bidder to state in writing:

• PS, TS and V for each chamber, or DN for piping
• the fluid group, Schedule 1B table and category for each chamber
• the module, and the name and number of the approved or notified body [1, 2]
• the marking: UKCA, CE, CE with UKNI, or none for SEP
• for a skid or other assembly, the category of each item and of the integration, set by the highest category other than safety accessories [1]

The declaration of conformity should name the procedure followed and any body, with its number and certificate reference [1]. For the design code, see our comparison of ASME VIII, PD 5500 and EN 13445.

Practical example

Five illustrative items for a pharma utility package. Air is group 2 here, as the Commission's guidelines read a compressed air tank's category from Table 2 [7].

Receiver A is 110 times the 50 bar·L limit, so it needs a category. Schedule 1B prints the boundaries only as charts, so we quote no band: plot 11 bar against 500 L on Table 2, where each line marks a category's upper limit, and have the manufacturer confirm category and module in writing [2].

D and E share one shell. Water at 10 bar escapes Table 4 because PS must also exceed 10 bar. Switch to E's solvent, or raise D to 16 bar (32,000 bar·L), and it moves into a category.

Find vendors who can build to your category

For a category III or IV vessel, the manufacturer needs an approved or notified body behind one of the permitted modules: an approved quality system (D, E, H or H1), or the body examining and testing the equipment itself (F, or G for unit verification) [1]. Supplier Discovery searches the web for suppliers from a plain text description, pasted RFQ or uploaded spec, and gives each a fit verdict with source links. Certifications are shown as claimed, not verified, so before award check the quality system certificate, or agree which body will verify the vessel.

Ready to find vendors who can build to your category? Start a free 14 day ChemCapital trial, with no credit card needed.