Every morning I am presented with the same challenge: what to wear. It’s not that there is anything wrong with any of the clothes in my wardrobe; individually each one is perfectly adequate for my needs. It’s just that I don’t have an eye for combining them.
My wife on the other hand has no such difficulty. She is able, seemingly without effort, to select and assemble various garments to create a stylish, integrated look; they function perfectly as a whole. Which is fortunate, as she tells me that one poorly chosen item (and shoes are apparently the worst culprits) can be fatal, figuratively speaking that is.
A manufacturer of an assembly faces a similar challenge, and it has a name: global conformity assessment. If you are not familiar, let me explain.
I suspect that this is best demonstrated by an example, albeit a hypothetical one. You would probably rather not be taken through the Pressure Equipment Directive line by line. But a word of caution: whether we like it or not, we are talking about statutory compliance, so it’s important that we don’t lose sight of where the obligations arise from. To prevent these details cluttering up the explanation, I have put them in the endnotes, but that doesn’t diminish their importance. If or when you have time, I recommend that you read the relevant parts of the Directive and Guidelines1.
Putting aside the word ‘global’ for one moment, let’s consider what’s meant by the words ‘conformity assessment’. Conformity assessment is the process carried out by a manufacturer to demonstrate that the relevant requirements of the Directive have been fulfilled. All items of pressure equipment and assemblies falling within PED category I to IV must be subject to a conformity assessment. Global conformity assessment2 is the name given to this process when it is applied to an assembly.
An assembly is several pieces of pressure equipment3 (i.e. vessels, piping, safety accessories, and pressure accessories) assembled by a manufacturer4 to constitute an integrated and functional whole5. In our example below, the assembly manufacturer has purchased a pressure vessel, relief valve, and a globe valve. Each of these items has been CE marked by their own respective manufacturers before they were placed on the market. The assembly manufacturer has fabricated the interconnecting piping, which in our case falls into category I.
A global conformity assessment procedure can be broken down into three steps. Let’s take one at a time:
The first thing that our assembly manufacturer must do is assess each category I to IV item of pressure equipment making up the assembly which has not been previously subjected to a conformity assessment and been CE marked. The assessment procedure is determined by the category of each item of pressure equipment6.
Immediately you can see that the purchased items don’t need to be considered, because they have already been CE marked, and so the respective manufacturers should have already undertaken the conformity assessment procedure. The only remaining item is the category I piping, and any of the conformity assessment modules7 could be applied to it by our assembly manufacturer, although Module A would be suitable and doesn’t require a notified body8.
The second thing that our assembly manufacturer must do is assess the integration of the various components of the assembly9. Now, those of you have read the Directive with a keen eye may have noticed that it only refers to three essential safety requirements in this regard10, but don’t be misled by this. Any of the Directive’s essential safety requirements must be satisfied if a corresponding hazard exists11.
But in assessing the integration of the components, which conformity assessment module should our assembly manufacturer use? Well, the choice of module is determined by the PED category. And for an assembly this will be the highest category of any of the items in our assembly, based on the conditions which can occur in the assembly12. In our assembly this item is the vessel. (By the way, we disregard the category of the relief valve, which has the highest category by default, because it’s a safety accessory.)
The vessel’s dataplate says that its design pressure is 20 bar, has a capacity of 80 litres and can be used for group 1 gases, and so it falls into category IV, as can be seen from HPiVS’s online calculator:
So, our assembly must be category IV, right? Well, no, not in our case. You see, the vessel manufacturer could not foresee all the applications that its vessel might be put to, and consequently it’s overengineered for the conditions which can occur in our assembly, i.e. a group 2 gas at up to 10 bar. When we apply those conditions to the vessel, it gives us category II, and consequently this is the category of our assembly. So, the assembly manufacturer could choose to apply Module A2, for example.
Before we move on to step three, now that we have ascertained that the vessel and assembly are category II, what category do you think the weld joining the vessel to the category I pipe is? Is it determined by the category of the vessel or the piping, as these are the items being joined, or perhaps by the category of the assembly? And more importantly, does it matter?
The category of the permanent joint13 between the items of pressure equipment of an assembly is determined individually (so in other words, not by the category of the assembly), considering the effect of the joining on the integrity of each of the items to be joined14.
If you look at the drawing, you will see that the vessel has nozzles, and these will have the same nominal diameter as the category I pipe. The connection of a pipe to a vessel through a nozzle is made according to the category of the pipe (provided that it does not affect the integrity of the vessel)15. Hence, in our case it’s a category I joint. Had there been no nozzle it would have been a category II joint, because that is the category of the vessel.
But why all the fuss? What does it matter? Well, it really does, because the category of the joint affects which obligations in the Directive our assembly manufacturer is required to meet. For a category I joint, the weld procedure simply needs to be ‘suitable’ and the welder need to be ‘suitably qualified’. For category II joints and above, however, the welding procedure and welder need to be approved by a Notified Body or Recognised Third Party Organisation16. In a similar vein, personnel undertaking NDT on category III or IV joints need be approved by a Recognised Third Party Organisation17.
The third thing that our assembly manufacturer must do is assess the protection of the assembly against its permissible operating limits being exceeded under reasonably foreseeable conditions18. In other words, the assembly should be fitted with suitable protective devices19 to prevent the minimum or maximum allowable pressure, temperature, or fluid level etc20 from being exceeded.
What are protective devices though? Well, they could be safety accessories such as relief valves, bursting discs and devices which activate the means for correction or shutdown21. Or it could be a combination of safety accessories and monitoring devices such as indicators and/or alarms which enable adequate action to be taken either automatically or manually to keep the assembly within its allowable limits22. However, monitoring devices alone won’t suffice23.
And last but not least, those safety devices should be checked at the final inspection to ensure that they have been installed24.
A FINAL WORD
Conformity assessment procedures are critical not only to demonstrating that an item of pressure equipment or assembly is in compliance with the Directive, but also ensuring that it is safe. Failing to do so could result in an injury or be fatal, and we’re not speaking figuratively this time.
A cornerstone of demonstrating compliance with the Directive is a hazard analysis and risk assessment, so we’ll look at that in the next issue.
In the meantime, I’ll try to work out what goes well with these mauve needlecord trousers.
- “Guidelines related to the Pressure Equipment Directive 2014/68/EU (PED)” can be downloaded for free from http://ec.europa.eu/DocsRoom/documents/23181
- See Article 14(6) for the global conformity assessment procedure.
- See Article 2(1) for the definition of pressure equipment.
- See Article 2(18) for the definition of a manufacturer.
- See Article 2(6) for the definition of assemblies. Also note that the last sentence of Recital 7 states that the Directive should not apply to the assembly of pressure equipment on the site and under the responsibility of a user who is not the manufacturer, as in the case of industrial installations.
- See Article 14 paragraph 6(a).
- Article 14 sets out which conformity assessment procedures are available for each category. A manufacturer may also choose to apply one of the procedures which apply to a higher category.
- The conformity assessment procedures are set out in Annex III, and these include details of the extent of a notified body’s involvement for each module.
- See Article 14 paragraph 6(b).
- Article 14 paragraph 6(b) refers to essential safety requirements 2.3, 2.8 and 2.9.
- See Guideline C-12.
- See Guideline C-16.
- See Article 2(13) for the definition of permanent joints.
- See the first paragraph of Guideline C15.
- See the second paragraph of Guideline C15.
- See essential safety requirement 3.1.2, which is in Annex I.
- See essential safety requirement 3.1.3, which is in Annex I.
- See Article 14 paragraph 6(c).
- See essential safety requirement 2.10, which is in Annex I.
- See Guideline A-43.
- See Article 2(4) for the definition of safety accessories.
- See essential safety requirement 2.10(b), which is in Annex I.
- See Guideline E-06.
- See essential safety requirement 3.2.3, which is in Annex I.