Fluxes and solders

I have not trained as a plumber and it is with some hesitation that I am writing about the skills which should be second nature to all plumbers. But recent experience shows that some plumbing work leaves much to be desired. The illegal use of lead solder and the improper use of flux are causing concerns about health risks amongst water suppliers, plumbing associations, water fit- tings manufacturers and health authorities.

Reasons for concern

In the past eighteen months, a young boy and his father, who had both been unwell for some time but without any clear causes, went to see their doctor, who recognised the signs of lead poisoning. Blood tests confirmed the diagnosis and detective work showed it was due to drinking water with excessive amounts of lead in it. The lead came from lead-based solder used in jointing the pipework.

In response to concerns about health effects of even low levels of lead in drinking water, since the 1980s lead based solder has been outlawed for use on' hot and cold water systems. Leaded solders can be used for non- drinking water systems such as closed circuit central heating pipework, where the water is not required to be wholesome. These requirements have been incorporated into the new Water Fittings Regulations (Water Byelaws 2000 in Scotland). Water Suppliers have the duty to enforce these regulations. Where the illegal use of lead-based solder is found in drinking water systems, the Water Supplier is likely to require all the joints to be remade at the installer's cost. The installer could also face a criminal charge and a fine.

Push-fit and press-fit fittings are alternatives to soldered joints. But where soldered joints are required or preferred, lead free solders are available either in integral solder ring fittings or for end-feed use. The use of a solder such as number 23 tin/copper alloy soft solder, made to EN 29453, will ensure that lead levels are not a problem. Not only is it suitable for all soldering work, but because it is less dense than lead solder, there's more on a 500gm reel, giving more joints per reel.

Flux helps molten solder to wet, adhere to and alloy with the copper tube. The change to lead- free solders with their higher melting points than the lead-based solder requires the use of an appropriate flux. For ordinary soft solder joints, fluxes made from zinc chloride or zinc ammonium chloride are usual. The manufacturers' advice should be followed. Modern fluxes, especially the self- cleaning types, can be more aggressive to the copper tube and need to be used with extreme care. Excess use of flux causes increased rates of corrosion of the pipework. There are examples where very high levels of copper and lead have occurred in water left in contact with poorly made joints suffering from excess flux residues. Ultimately, excessive corrosion can lead to premature failure of the pipework and leaks.

After deburring a cut tube end inside and out, the outside of the tube should be cleaned, with the green abrasive impregnated nylon kitchen scouring pad recommended for domestic use to avoid steel wool fragments in the system. Flux should NOT be applied to the fittings, but immediately after cleaning a thin coating should be applied to the outside of the tube only. Assemble immediately to avoid contamination by dirt or dust and distribute the flux internally by twisting the fitting onto the tube. Wipe off any excess flux. Heating the tube and fitting should be even and only hot enough to melt the solder. Hotter than this risks charring the flux. For integral fittings, gentle even heating until a complete ring of solder appears at the mouth of the fitting is sufficient. Resist the temptation to end feed additional solder to an integral ring fitting. For end feed joints, the tube and fitting should be heated sufficiently so that, with the heat source removed, the solder melts and flows into the joint when touched onto the tube. Avoid using too much solder; for small tube joints using solder wire, a length equal to the tube diameter should be sufficient to fill the joint.

Flushing

After the joint has cooled, residual flux should be cleaned from the outside with warm water. The pipeline should be flushed to remove flux residues and any debris, using cold water for water based fluxes, but hot water is better for grease-based fluxes which may not be removed by cold water flushing.