Lead from pipework

Containment of potential pollutants should ensure that no accidental releases to the environment occur under normal operational circumstances. However, if a minor leakage/spillage was to occur and go undetected for other than a short time scale, sufficient volume of pollutants could be lost to result in environmental deterioration equivalent to a major environmental accident. Typically, imdetected chronic leakage occurs in association with the storage of raw materials and wastes radier than during use, e.g., from pipework leading to and from storage. 

The water supply authorities normally insist that (for uses other than drinking-water taps) their main should discharge into a break-pressure vessel, after which the water quality becomes the consumers responsibility. The water tank should be covered against tramp dirt and access by birds, etc., and it must be shielded from sunlight to avoid the growth of algae. Nevertheless, access must be maintained for easy inspection. The distribution pipework is preferably all plastic and lead must be avoided altogether. The use of copper is doubtful with some corrosive waters, and soldered joints in it can lead to unacceptable concentrations of lead in the water. 

The proximity of the anodes to structures is also important. For example, if the sacrificial anodes are placed on, or very close to, steel pipework in soil then the output from the face of the anodes next to the steelwork can be severely limited. Alternatively, in high conductivity environments, corrosion products may build up and wedge between the anode and the structure. The resulting stresses can lead to mechanical failure of the anode. On the other hand, when anodes are located at an appreciable distance from the steelwork, part of the potential difference will be consumed in overcoming the environmental resistance between the anode and cathode. 

From 1983 until its shutdown in 1994 PFR experienced cracking in type 321 stainless steel components in its secondary circuits, some cracks leading to sodium leaks. As a result a substantial repair and inspection programme was required in the final seven years of PFR operation. Although the two earliest leaks were in pipework (in 1983 and 1986) the majority were in steam generator vessels. The pipework leaks were only retrospectively identified as being caused by the same mechanism. 

In the induced jarosite precipitation and primary neutralization processes, this is typically done in-slurry, at temperatures in excess of 80°C. Few issues with scale formation occur, apparently due to the presence of a large surface area available from the leach residue solids, relative to equipment surfaces. It is important to provide adequate retention time for the complete reaction of the limestone, to avoid reactions continuing to occur in downstream thickeners and pipework. Such reactions can lead to both process upsets and scale formation over the longer term. 

Particular attention must be given to transfer pipework where seam-welded pipe runs are used. In such cases, experience from the American power industry steam reheat line catastrophic failures should be borne in mind. The critical factors identified are weld geometry, weld metal and flux compositions and pipe ovality. Generally, older CRU units utilise seamless pipe in this service but some instances are known, particularly in larger capacity units, where seam-welded pipe is in service. Where necessary, this factor can be taken into account in the assessment procedure described below. Seam welds are subject to the full pressure hoop stress, as well as to many of the system loads. Failure of such a weld is likely to lead to a full-scale rupture, rather than a leak. Accordingly, they must be treated as critical items for assessment, and replacement, rather than repair, should be considered the ultimate outcome. 

The electrolysis was performed in stacks of 24 cells mounted in a filterprcss (Fig. 6 J) and the anolyte and catholyte flows were each in parallel from single reservoirs. Each cell is a relatively complex structure with lead cathode, catholyte chamber, turbulence promoter, membrane, anolyte chamber and lead alloy anode. The celt must be gasketed and each electrolyte chamber must have pipework attached at inlet and outlet and a flow distributor to give an even electrolyte flow, Even so, the cell had to be designed to minimize the interelectrode gap since energy consumption was a consideration and the catholyte and membrane had relatively high resistances. Moreover, rapid dismantling and replacement of membranes was essential... 

To obtain steady flow conditions, relatively long feed pipes to the elutriator are necessary. If there are any sharp bends in the feed pipework leading to or from the main tube, flow conditions are hard to predict and fractionation performance has... 

The extrudable adhesives are supplied in the larger sized containers, 22-5 or 200 litres, which have been filled under controlled conditions to avoid the occlusion of air. The adhesive is distributed to the work locations from a centrally sited pump-house through a manifolded pipe network at moderate pressure. Care must be taken in the design of the pipework to ensure that there are no features which may lead to eventual partial or full blockages. A dual pumping system is normally used the adhesive is transferred from one container at a time and as the end is approached the system will automatically switch over to the other thereby providing a constant material supply. 

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