At a glance
- An assembly is not every collection of connected equipment. Article 2(6) requires three things at once: integrated, functional, and assembled by a manufacturer.
- Where the user assembles on his own premises, it is not an assembly but an installation, and that assembling falls outside the directive (recital 7) — the individual items, and the joining of components into one item, do not. In the Netherlands that runs via Article 17a of the WBDA 2016.
- Where all parts already carry a CE marking, only the assessment of those parts falls away. The assessment of the integration and of the protection remains (Article 14(6)(b) and (c)), plus a declaration and a CE marking of your own.
- An assembly gets no category of its own. The directive assigns two governing categories: one for the integration (safety accessories are left out) and one for the protection.
What you will find on this page
- What the directive calls an assembly — the definition and the four criteria
- Assembly or installation? — the decision tree, and why that distinction decides everything
- Who is the manufacturer — and when you become one without meaning to
- All parts already CE marked — what is still required
- Which category applies — two governing categories, none for the whole
- The Netherlands — in-house assembly, and why an assembly is not subject to inspection as such
- When it stays outside the assessment — and the exception for fired assemblies
- Five misconceptions — with the provision that refutes each
What the directive calls an assembly
The definition is short. Article 2(6) calls an assembly several pieces of pressure equipment assembled by a manufacturer to constitute an integrated and functional whole. Three elements, and they apply together. If one is missing there is no assembly within the meaning of the directive — however sensibly the whole may work.
Recital 7 makes the reach concrete: an assembly may range from a pressure cooker to a water-tube boiler, and the directive applies where the manufacturer intends the whole to be placed on the market and put into service as an assembly. That same recital excludes one case just as expressly: assembly under the responsibility of a user who is not the manufacturer, such as an industrial installation on his own premises.
The four criteria
The directive itself gives three elements; the Working Group Pressure worked them into four testable criteria. There is an assembly where the items are:
| Criterion | What it means |
|---|---|
| Integrated | they are connected and matched to work together — not merely tied to one another |
| Functional | together they achieve a defined purpose and can be put into service |
| A whole | everything needed to function and to be safe is present — including the protection |
| By one manufacturer | one party assembles, intends the whole for the market and submits it to a global conformity assessment |
Assembly or installation? That distinction decides everything
The directive does not know installation as a defined concept — the word does appear in it, in recital 7 and in Article 1(2)(a) among others, but not as a legal figure. The guidelines do use it, and for a reason: guideline 3/2 notes that where items are being put together by a user, the term installation is used to avoid confusion. It is the counterpart of the assembly. Where the manufacturer assembles, it is an assembly and the PED applies to the whole. Where the user assembles under his own responsibility, it is an installation and national law applies to the whole — while the individual items keep their own CE marking.
Two misunderstandings sit opposite each other here, and both are half true:
“Building on site is never an assembly”
Wrong. Guideline 3/8 says expressly that it makes no difference whether the assembly is completed in the manufacturer's workshop or by the manufacturer on site. A fitter finishing the job on behalf of the supplier is building an assembly.
“Whoever connects on site is automatically the manufacturer”
Also wrong. What decides is not the place but the responsibility. Where the user assembles for his own use, that falls outside the directive (recital 7) and is called an installation.
Joining on site: two cases
Guideline 3/2 draws a sharp line. Join components into one item of pressure equipment — a shell to its ends, a pipe run from pipe sections — and that joining falls under the directive, even where you are the user: a new item of pressure equipment comes into being and somebody is its manufacturer. Join complete items of pressure equipment into a whole and it depends on the responsibility: under your responsibility as manufacturer it is an assembly, under the user's an installation.
Who is the manufacturer
Article 2(18) is impersonal and therefore inescapable: the manufacturer is whoever manufactures pressure equipment or an assembly, or has it designed or manufactured, and markets it under his own name or trade mark or uses it for his own purposes. Those last seven words are where most companies get it wrong: you do not have to sell anything to be the manufacturer.
What the manufacturer of an assembly must do is in Article 6: design and manufacture in accordance with Annex I (paragraph 1), draw up the technical documentation of Annex III and carry out or have carried out the procedure of Article 14, and then — once the procedure has been passed — draw up the EU declaration of conformity and affix the CE marking (paragraph 2). By drawing up that declaration he assumes responsibility for the assembly (Article 17(4)).
All parts already CE marked: what is still required?
This is the question on which installations founder in practice, and the answer is short: three things, one of which falls away. Article 14(6) prescribes a global conformity assessment for an assembly that consists of three assessments.
| What is assessed | Does it apply where the parts are CE marked? | |
|---|---|---|
| a | the conformity of each individual item of pressure equipment in the assembly | No — this element applies expressly only where the item has not already undergone its own procedure and received its own CE marking |
| b | the integration of the parts, against Annex I, 2.3, 2.8 and 2.9 | Yes, in full |
| c | the protection of the assembly against exceeding the permissible operating limits, against Annex I, 2.10 and 3.2.3 | Yes, in full |
On top of that, paragraph 6 is not an exhaustive list. Guideline C-12 answers precisely that question with a “no”: on the basis of Annex I, preliminary observations 1, the whole of Annex I applies to assemblies where the corresponding hazard exists. The guideline itself gives as examples 3.1.2 (permanent joining), 3.2.2 (proof test), 3.4 (operating instructions) and 6(a) and (d) (expansion and vibration of piping).
And the declaration and the marking
The assembly gets an own EU declaration of conformity (Article 6(2), second subparagraph) and an own CE marking on the assembly or on its dataplate (Article 19(1)(b)). The individual items need not be marked again, and whatever already carried a CE marking keeps it (Article 19(2)). In the declaration for the assembly you describe all the pressure equipment it consists of, stating the conformity assessment procedure followed for each PED item — that is what guideline J-08 takes from Annex IV, point 4. The remaining parts, including equipment under Article 4(3) and equipment excluded from the directive, are described as well but carry no procedure.
Which category applies to an assembly
None. That is the answer you will read in no summary, and it is the answer the directive gives. An assembly gets no category of its own; Article 14(6) designates two governing categories for two different assessments:
- For the integration (under (b)): the highest category applicable to the equipment concerned, other than that applicable to any safety accessories. That last part is no detail: safety accessories are in principle category IV under Annex II, point 2, and without that exception every assembly with a safety valve would end up in category IV.
- For the protection (under (c)): the highest risk category of the items to be protected. That may be a different category from the one governing the integration.
For the remaining essential requirements the directive is silent about the category. Guideline C-15, note 1, then says: base those on the categories of the items concerned. And permanent joints are assessed joint by joint, not over the whole.
When an assembly stays outside the assessment
Two conditions must hold together before Article 4(2)(b) brings an assembly under the directive: it contains at least one item of pressure equipment that itself falls under Article 4(1), and the manufacturer intends the whole to be made available on the market and put into service as an assembly.
Where that second condition drops out — because your skid is meant to become part of a larger assembly or of an installation, say — there is no global conformity assessment over the whole and no CE marking goes on it. The individual items keep their own assessment and marking. That is in guideline 3/10 of the old bundle and follows directly from the words “intended to be” in Article 4(2)(b).
Where the characteristics stay within or equal to the limits of Article 4(1)(a), (b) and (c) and of Article 4(2), Article 4(3) applies to assemblies as well: sound engineering practice, adequate operating instructions, and expressly no CE marking under this directive. See Article 4(3) (SEP).
The Netherlands: in-house assembly, and the duty of inspection
The Dutch Pressure Equipment Decree 2016 takes its concepts from the directive (Article 1(1)(u) for assemblies) and prohibits in Article 2(1) and (3) the placing on the market, putting into service, offering or use of assemblies that do not meet the requirements or for which the prescribed procedures have not been carried out.
Assembling for your own use?
Then Article 17a applies, and that is the provision most often missed in the Netherlands. Users who assemble pressure equipment or assemblies in-house for their own purposes comply with a listed series of articles of the directive, including Articles 6, 13, 14 and 17 and Annex I (paragraph 1). The assessment is carried out by an NL conformity assessment body (paragraph 2), and the result is an NL declaration of conformity in Dutch or English (paragraph 4) — not a CE marking. That is no omission: this equipment is not placed on the market but built by the user for his own purposes, and the decree requires the CE marking only for equipment that does reach the market.
Is an assembly subject to inspection?
Not as an assembly. The Dutch word for assembly, “samenstel”, does not occur anywhere in the Dutch Pressure Equipment Regulation 2016. Article 21(1) of the decree allows pressure equipment to be designated by ministerial regulation, and Article 2 of the regulation designates pressure vessels and installation piping with their safety accessories and pressure accessories, by table of Annex II. So the inspection before commissioning and the periodic re-inspection attach to the individual vessels and pipe runs inside your assembly, each with its own table and category. Article 21(12) confirms this: one declaration of commissioning may cover several items. And paragraph 9 covers the case you meet most often when extending an existing installation: where an individual vessel or pipe run is coupled to an existing vessel or pipe run, the inspection before commissioning may be related to that individual item. So it is a coupling rule, not a general exemption. Work it out with the Dutch inspection check.
Five misconceptions, with the provision that refutes each
| What gets said | What the text says |
|---|---|
| “An assembly takes the category of its highest-classified part” | The directive assigns no category to the assembly. Article 14(6)(b) and (c) gives two governing categories for two assessments, and for the integration safety accessories are expressly left out. |
| “All the parts are CE marked, so we are done” | Only element (a) of Article 14(6) falls away. The integration (b) and the protection (c) remain, plus a declaration of your own (Article 6(2)) and a CE marking of your own (Article 19(1)(b)). |
| “Whoever connects on site is automatically the manufacturer” | What decides is the responsibility, not the place. Assembly under the responsibility of the user falls outside the directive (recital 7) and is called an installation; in the Netherlands that runs via WBDA Article 17a. |
| “Items that are connected and work together form an assembly” | Article 4(2)(b) also requires the intention to make the whole available on the market and put it into service as an assembly. Mind the exception in (a): assemblies for steam or superheated water above 110 °C containing a fired or otherwise heated item fall under the directive without that intention requirement. And guideline B-40: an accessory with a safety accessory on it is not an assembly, since it is not a functional whole. |
| “Only the points in Article 14(6) apply to the assembly” | Guideline C-12: no. Annex I applies in its entirety to assemblies where the hazard exists, including 3.1.2, 3.2.2, 3.4 and 6(a) and (d). |
Frequently asked questions
When do separate items of pressure equipment form an assembly under the PED?
Where three things hold at once (Article 2(6)): the items are integrated, they constitute a functional whole, and they have been assembled by a manufacturer. Article 4(2)(b) adds that at least one item under Article 4(1) is included and that the manufacturer intends the whole to be made available on the market and put into service as an assembly. Under (a) that intention requirement does not apply: assemblies for steam or superheated water above 110 °C containing a fired or otherwise heated item fall under the directive in any event. If one element is missing there is no assembly within the meaning of the directive.
Do I have to affix my own CE marking if all the parts are already CE marked?
Yes. Article 19(1)(b) requires the CE marking on the assembly or on its dataplate, and Article 6(2) requires an EU declaration of conformity of your own. What does fall away where the parts are CE marked is the assessment of those parts themselves (Article 14(6)(a)); the assessment of the integration and of the protection remains. The parts keep their own marking (Article 19(2)).
What is the difference between an assembly and an installation?
The responsibility for the assembling. Where a manufacturer assembles, it is an assembly and the PED applies to the whole. Where the user assembles under his own responsibility on his own premises, that falls outside the directive (recital 7) and the guidelines speak of an installation. The place makes no difference: a manufacturer finishing the job on site is still building an assembly.
Which category does my assembly have?
None. Article 14(6) designates two governing categories: for the assessment of the integration, that of the item with the highest risk category without counting the safety accessories, and for the assessment of the protection, the highest category of the items to be protected. The two may differ. There is no Article 13(3) giving an assembly a single category.
Does an assembly have to be inspected before commissioning in the Netherlands?
Not as an assembly. The Dutch word “samenstel” does not occur in the Dutch Pressure Equipment Regulation 2016: Article 2 designates pressure vessels and installation piping with their accessories, by table of Annex II of the directive. So the duty of inspection attaches to the individual vessels and pipe runs in your assembly, each with its own category. WBDA Article 21(12) allows one declaration of commissioning to cover several items, and paragraph 9 allows the inspection to be related to the individual item where it is coupled to an existing vessel or pipe run.
Not sure whether you are the manufacturer of this assembly?
Put your case on paper once, with the provisions next to it. The full report gives the category per item, the governing category for the integration and the file list; the classification appraisal adds my written opinion. For the file itself there is a template set for assemblies and product families.
Run the free check or see the full report