Besides the few authors to whom we have given slightly more exposure, others have used the notion especially for descriptive, explanatory or even normative reasons. Sometimes moving away from what the notion means from the implicit standardisation point of view, they have used it as a translation vehicle between heterogeneous worlds. In the end, the notion describes any interface mechanism between knowledge or actors. It seems to have lost its original analytical momentum, i.e. the fact that certain objects or configurations – or even organisations – materialise and transport an invisible infrastructure made up of standards, categories, Classifying Equipment and conventions that are specific to one or more social worlds.

To establish which category applies to the equipment, the manufacturer must use the charts 1 to 9 given within the Directive to plot the pressure against the volume of a vessel or against the diameter of a pipe. Where the manufacturer has an assembly of pressure equipment, each individual section of the system has to be reviewed against the relevant charts and then the high category will then dictate the route to conformity. One exception to using the charts is for safety components/accessories; which are automatically classified as category IV equipment. This is, however, only when they are being placed on the market by themselves. Where a safety component is incorporated into a larger assembly, then the classification of this component is changed to the highest category of the other parts of the system.

The Directive applies to the design, manufacture and conformity assessment of pressure equipment (which includes vessels, pipes, accessories and safety components) and assemblies of such equipment where the maximum allowable pressure is greater than 0.5 bar. As I am sure that you can imagine, as the pressure and volume increase, so does the risks associated with the equipment or assembly. The Pressure Equipment Directive deals with this by setting five categories of equipment; SEP, I, II, III & IV (The higher the pressure and volume, then higher the category). CE marking only applies to categories I to IV, where SEP (standing for 'Sound Engineering Practice') cannot be CE Marked under PED and purely requires the manufacturer to use common sense.

Where equipment is being placed on the market in Europe that has a positive pressure that is greater than 0.5 bar, then Pressure Equipment Directive must be considered. The Directive, usually shortened to 'PED' came into force in 1999 and applies to arrange of equipment under pressure, however not all pressure equipment can be CE marked.

This study provides an up-to-date review of recycling of printed circuit boards (PCBs), specifically in Hydrometallurgy Equipment. Waste printed circuit boards, which are rich in base and precious metals, are the essential component of end-of-life electrical and electronic equipment. From the economic and environmental perspectives, the efficient recycling of PCBs is of importance. For the extraction of metals from PCBs, a large amount of work has been done to establish an environmentally friendly and economic way to recover metals from PCBs based on physical, pyrometallurgical and hydrometallurgical processes. Among those processes, hydrometallurgy is a promising treatment due to its low capital cost, high selectivity and lower environmental impact. This review emphasizes the recycling of PCBs by physical and hydrometallurgical treatments.

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