Machine builders and the Pressure Equipment Directive 97/23/EC

It is not unusual for machine builders to encounter situations where they suspect that part of the equipment they are producing falls within the scope of the European Pressure Equipment Directive 97/23/EC, which is implemented in the UK as the Pressure Equipment Regulations 1999 (PER). While such situations may raise fears of costly and time-consuming third-party testing and compliance procedures, these are by no means always necessary.

Before assuming the worst, therefore, it is worthwhile following the step-by-step procedure outlined in this article to determine whether a simpler route to compliance is, in fact, all that is needed.

Step 1 - Check the scope

The first step is to decide whether the equipment under consideration really does fall within the scope of the Pressure Equipment Directive. In general terms, the regulations apply to pressure equipment and assemblies of pressure equipment with a maximum allowable pressure of more than 0.5bar, where pressure equipment is defined as vessels, piping, safety accessories and pressure accessories.

There are a number of exclusions, and information about these can be found in publication from the DTI (now known as the Department for Business, Innovation & Skills) reference URN 05/1074, Pressure Equipment - Guidance Notes on the UK Regulations. This can be downloaded free of charge from the BIS website (580kB PDF). At the time of writing, the most recent list of Harmonised Standards for the Pressure Equipment Directive was published in the Official Journal (OJ) of the European Union on 15 April 2011; this can be accessed via the European Commission website.

For machine builders, paragraph 10 in Annex A of this document, which corresponds with Clause 3.10 of the Directive, may be of particular interest, as this details specific exclusions relating to machinery. Care should be taken when relying on these exclusions, however, as the wording is, to some extent at least, open to interpretation. In case of doubt, it is always preferable to proceed on the basis that the equipment is in fact covered by the PER.

Step 2 - Equipment type and fluids

Having decided that the equipment is covered by the PER, the next step is to decide whether it should be categorised as a vessel, which is defined as a housing designed and built to contain fluids under pressure; piping, which covers components intended for the transport of fluids when connected together for integration into a pressure system; or a steam generator, such as a boiler. It is also necessary to decide, except in the case of a steam generator, whether the fluid contained in the equipment is a gas or a liquid, and whether the fluid has to be treated as a Group 1 or Group 2 fluid.

The decision about whether the fluid is a gas or a liquid is usually straightforward but, if there is any doubt, the regulations require the fluid to be treated as a gas if it has vapour pressure greater than 0.5bar at the maximum allowable temperature for the equipment. Information about vapour pressure at various temperatures should be readily available from the supplier of the fluid. Deciding between Group 1 and Group 2 fluids is equally straightforward, as Group 1 covers fluids that are explosive, flammable, toxic or oxidising, with all other fluids falling in to Group 2.

Step 3 - Product classification

With these simple decisions made, the next stage in the process is to refer to the product classification table contained in the BIS publication mentioned earlier, which is reproduced here (see right). Depending on the type of equipment, the type of fluid and whether it is a gas or a liquid, this table indicates which of the nine charts contained in Annex B of the publication must be used to determine the required method of compliance with the PER.

One of these charts is reproduced below, and it will be seen that this has volume along the horizontal axis and pressure on the vertical axis. To use the chart, the point corresponding to the volume of the equipment under consideration and the maximum pressure to which it will be subject is located on the chart. This point will fall into one of the five regions defined by the curves on the chart. The regions are identified as SEP, I, II, III and IV and these indicate the category of the equipment. It is this category that determines the procedures that must be followed in order to achieve compliance with the PER.

For pipework, where the volume is not easily determined, the charts use instead a nominal size (DN). This is only loosely related to the pipe's physical diameter, and the DN figure should, therefore, be obtained from the manufacturer or supplier of the pipe.

Compliance procedures for SEP and Category I

If the equipment under consideration is found to be in the SEP (sound engineering practice) category, no special measures are needed to comply with the PER, but the equipment must still, of course, meet the requirements of the regulations that implement the Machinery Directive 2006/42/EC. Note that equipment in this category is NOT permitted to carry CE marking to indicate compliance with the PER.

For equipment in category 1, the compliance requirements are almost equally modest. All that is necessary, in addition to the usual requirements relating to the Machinery Directive, is to produce technical documentation that can be used as the basis of an assessment to show that the equipment conforms to the regulations, and which covers its design, manufacture and use. In contrast to SEP equipment, category 1 equipment must carry the CE marking.

It will be seen that achieving compliance with the PER for SEP and category 1 equipment, which often turns out to be the situation machine builders need to address, is a relatively straightforward and inexpensive process. It is also worth noting that for equipment in these categories, it is not necessary to involve a Notified Body in the PER compliance process.

These cases are, in fact, explicitly covered in the Directive, where Clause 3.6 creates a specific exclusion for equipment that is classified as no higher than category 1. At first sight this is a useful exclusion that eliminates the need to go through the processes described in this article. Unfortunately, as a moment's reflection will reveal, the only way to decide whether the equipment should be "classified as no higher than category 1" is to make an initial assessment as outlined above, so Clause 3.6 is rather less helpful than it might seem.

Compliance procedures for Categories II, III and IV

Turning now to equipment in categories II, III and IV, it has to be said that a much more in-depth compliance procedure is needed, and that it is necessary to work in conjunction with a Notified Body. It is not possible to discuss these requirements in this short article, but full details are contained in the BIS publication. It is worth mentioning, however, that even with equipment in these higher categories, a choice of modules that can be used to show compliance is offered, so suppliers can choose the modules that suit them best.

Before concluding, it is important to note that all of the information contained in this article is provided for general guidance only. While the article has been prepared with care, its contents should not be regarded as definitive and decisions relating to pressure equipment should only be made after referring directly to the Pressure Equipment Regulations 1999.

As we have seen, there are many instances when achieving compliance with the PER is a far less challenging process than is often imagined. Nevertheless, it is not a process that machine builders can afford to get wrong, so it is often desirable to call on expert advice from a consultant with experience in this field, such as Laidler Associates.

Advice of this type can save machine builders a lot of time and money, as well as providing them with complete confidence that all of the necessary procedures involved with compliance with the pressure Equipment Directive and Pressure Equipment Regulations have been properly carried out. Or, to put it another way, a modest investment in consultancy will do a lot to relieve the pressure! Follow the link for more information about the services Laidler Associates offers in relation to the Pressure Equipment Directive 97/23/EC.