PED Conformity Assessment Modules Explained: Categories I to IV
Direct answer: The Pressure Equipment Directive (PED) 2014/68/EU sorts pressure equipment into four risk categories, I to IV, based on a combination of fluid type, pressure and size (volume or diameter). Category I allows the manufacturer to self-certify; Categories II, III and IV require progressively deeper involvement from an independent Notified Body, from spot checks at production through to full quality assurance audits of design and manufacture. The category determines which conformity assessment "module" — essentially, which certification route — a manufacturer must follow before affixing the CE mark.
If you manufacture, import or specify pressure vessels, boilers, piping, safety accessories or pressure-related assemblies for the EU market, PED compliance is not optional — it is the legal gateway to CE marking. But unlike ISO management-system standards, PED is not built around a linear sequence of numbered clauses. It is a product directive under the EU's New Legislative Framework, and its logic runs differently: define the scope, classify the risk, then match that risk to a certification route. Understanding that logic — rather than trying to force it into a clause-by-clause checklist — is the fastest way to get compliance right the first time.
What PED actually is, and what it covers
PED 2014/68/EU is an EU product directive, not a management-system standard. It sits within the New Legislative Framework, the same regulatory architecture that governs machinery, low-voltage equipment and other CE-marked product categories. Its purpose is to harmonise the safety requirements for pressure equipment and assemblies placed on the EU market, so that a vessel or piping system certified compliant in one member state can move freely across the others without re-testing.
The directive applies to pressure equipment and assemblies with a maximum allowable pressure (PS) greater than 0.5 bar. This threshold is deliberately low: it captures everything from small compressed-air vessels and steam boilers to large-diameter industrial piping and safety accessories such as valves and rupture discs. Equipment operating below 0.5 bar generally falls outside PED's scope and may be governed by other CE directives or general product safety rules instead.
How risk categorisation works (Annex II)
PED's Annex II is where equipment gets sorted into one of four categories — I, II, III or IV — in ascending order of risk and regulatory scrutiny. The classification is not a single formula or risk score; it is a table-based lookup that cross-references two variables:
- The fluid group. Annex II distinguishes between Group 1 fluids (classified as dangerous — for example explosive, flammable, toxic or oxidising substances) and Group 2 fluids (essentially everything else, including steam and compressed air under normal conditions). Group 1 fluids attract stricter categorisation at equivalent pressure and size than Group 2 fluids, because the consequences of failure are more severe.
- Pressure combined with size. For vessels, the relevant combination is maximum allowable pressure (PS) multiplied against volume (V). For piping, it is PS combined against nominal diameter (DN). Annex II provides a set of diagrams and tables, specific to each equipment type and fluid group, that plot these combinations and read off the resulting category.
In practice, this means two pieces of equipment holding identical fluids at identical pressures can land in different categories purely because one has a larger volume or diameter than the other. Because the actual numeric thresholds in these tables are precise, equipment-type-specific and subject to the directive's exact wording, they should always be read directly from Annex II — or verified with a Notified Body or compliance specialist — rather than approximated. Getting the category wrong at this stage cascades into every downstream compliance decision, including which conformity assessment module applies and whether a Notified Body needs to be involved at all.
Essential Safety Requirements: the baseline every category must meet (Annex I)
Regardless of category, all pressure equipment placed on the EU market under PED must satisfy the Essential Safety Requirements set out in Annex I. These cover the technical substance of safe design: material selection and traceability, design calculations against foreseeable loads, manufacturing process controls (including welding procedure qualification where relevant), and final testing — typically a pressure test — before the equipment is put into service. Category does not change what safety is required; it changes how rigorously, and by whom, compliance with that safety baseline is verified and documented.
Once equipment is assigned a category, PED specifies which conformity assessment "modules" — standardised certification procedures shared across New Legislative Framework directives — the manufacturer may use. The manufacturer typically has a choice among several equivalent modules within a category, and the burden of proof shifts progressively from manufacturer self-declaration toward independent Notified Body verification as category rises.
| Category |
Typical modules |
Notified Body involvement |
| I |
Module A |
None — manufacturer self-certification under internal production control |
| II |
Module A2, D1, E1 |
Involved at production stage (e.g. random product checks or oversight of production quality controls) |
| III |
Module B+D, B+F, B+E, B1+D, G, H |
Involved in both design examination and production oversight |
| IV |
Module B+D, B+F, G, H1 |
Most extensive — involved at all stages, typically under full quality assurance |
Category I is the lightest-touch route: the manufacturer self-certifies under Module A, meaning internal production control without third-party sign-off. This is appropriate for equipment that Annex II's tables place at the lowest combination of fluid risk, pressure and size.
Category II introduces a Notified Body into the picture, but only at the production stage — for example under Module A2 (supervised checks at random intervals), D1 (quality assurance of production) or E1 (quality assurance of final inspection and testing). Design itself is not independently reviewed at this level.
Category III is where design and production both come under independent scrutiny. Manufacturers typically choose between combined-module routes such as B+D (EU-type examination plus production quality assurance), B+F (type examination plus product verification), B+E, B1+D, or single comprehensive modules like G (unit verification) or H (full quality assurance). The common thread is that a Notified Body now reviews the design as well as how it is produced.
Category IV carries the most demanding assessment burden. Routes include B+D, B+F, G or H1 — the latter being full quality assurance with design examination, the most exhaustive combination in the PED module set. Equipment at this level typically represents the highest combination of hazardous fluid, pressure and size, and the Notified Body's oversight extends across design, manufacture and final verification.
What compliance actually produces
Successful conformity assessment under PED results in three concrete outputs: the CE mark affixed to the equipment, an EU Declaration of Conformity issued by the manufacturer, and — for categories and modules that require Notified Body involvement — that body's four-digit identification number displayed alongside the CE mark. The identification number is a visible signal to customers, installers and market surveillance authorities that independent verification, not just self-declaration, sits behind the mark.
Why higher categories connect to your quality management system
Several of the higher-category modules — notably D, E, H and H1 — require the manufacturer to operate a certified quality management system as part of the conformity route itself, not as an optional extra. A Notified Body auditing a Module H1 route, for example, is not just checking a single vessel; it is assessing whether the manufacturer's design and production quality system reliably produces compliant equipment over time. This is precisely where PED intersects with ISO 9001: a manufacturer with an already-certified ISO 9001 quality management system has a substantial head start when pursuing Category III or IV routes, because the process discipline, documentation control and corrective-action mechanisms ISO 9001 requires overlap heavily with what PED's higher-category modules expect to see.
Common mistakes manufacturers make
- Misreading Annex II as a single formula. Treating categorisation as "one number in, one category out" leads teams to skip the correct table for their specific equipment type and fluid group, producing the wrong category — and the wrong module — from the start.
- Assuming Category I means no obligations. Self-certification under Module A still requires full compliance with the Essential Safety Requirements of Annex I and a properly issued Declaration of Conformity. It removes third-party sign-off, not the underlying safety obligation.
- Choosing a module without checking Notified Body scope. Not every Notified Body is accredited for every equipment type, fluid group or module. Engaging one only to find they cannot cover your specific scope wastes time at the worst possible stage of a project.
- Leaving quality system certification to the last minute. Modules that require a certified quality management system (D, E, H, H1) cannot be bolted on days before a Notified Body audit. Manufacturers pursuing Category III or IV equipment should treat ISO 9001 certification as a prerequisite project, not an afterthought.
- Failing to keep the technical documentation current. The Declaration of Conformity and supporting technical file need to stay aligned with the actual equipment as manufactured — including any post-certification design changes — not just the version originally assessed.
Where AI-assisted document search helps
Quality and compliance teams navigating PED often juggle multiple documents at once: the Annex II classification tables, internal design files, Notified Body correspondence, and the quality manual underpinning a Module H or H1 route. IgeraIndustria is built for exactly this kind of navigation — it answers questions directly from a company's own compliance and quality documents, citing the exact source clause or page, so a technical or quality manager can confirm what their own documentation actually says about a given equipment classification or module requirement without manually re-reading every file.
Frequently asked questions
What pressure threshold brings equipment into PED's scope?
PED 2014/68/EU applies to pressure equipment and assemblies with a maximum allowable pressure (PS) greater than 0.5 bar. Equipment below that threshold generally sits outside the directive's scope.
Is PED categorisation based on a single risk score?
No. Annex II uses a table-based lookup that cross-references fluid group (Group 1 dangerous fluids, Group 2 other fluids) against pressure combined with volume (for vessels) or nominal diameter (for piping). There is no single formula — the correct table for the specific equipment type must be consulted directly.
Can a manufacturer self-certify Category I equipment?
Yes. Category I equipment typically follows Module A, allowing the manufacturer to self-certify under internal production control without Notified Body involvement, provided the Essential Safety Requirements in Annex I are met.
At what category does a Notified Body become mandatory?
From Category II upward. Category II requires Notified Body involvement at the production stage; Categories III and IV require involvement in both design and production, with Category IV requiring the most extensive oversight, typically under full quality assurance.
Does every PED module require a certified quality management system?
No, but several higher-category modules do. Modules D, E, H and H1 in particular require the manufacturer to operate a certified quality management system, typically aligned with standards such as ISO 9001, as part of the conformity assessment route itself.
What does the Notified Body identification number on a product mean?
It confirms that an independent Notified Body was involved in verifying conformity, as required for the equipment's category and chosen module, and that this verification was not based on manufacturer self-declaration alone.
Where can I find the exact numeric thresholds for PED categories?
Directly in Annex II of PED 2014/68/EU, which contains the specific diagrams and tables for each equipment type and fluid group. Because these values are precise and equipment-specific, they should be read from the directive itself or confirmed with a Notified Body or qualified compliance consultant rather than approximated.
Disclaimer: This article is provided for general informational purposes only and does not constitute legal, certification or regulatory advice. PED categorisation and module selection depend on the specific technical characteristics of your equipment and must be verified against the current text of Directive 2014/68/EU and its annexes. Always consult a qualified compliance consultant, certification body or lawyer before making conformity assessment decisions.
