When stainless steel pipework is used in plumbing systems, joining can be expensive, time consuming and difficult. There is an incentive to use simple joining methods which will increase the popularity of stainless steel installations for industrial and domestic use. This opportunity was pursued by Lancashire Fittings in association with British Steel.
• mechanical fastening (fittings are expensive);
• soldering (time consuming, careful cleaning needed, uses corrosive chemicals);
• adhesive bonding.
What Was Done
A study by Lancashire Fittings in association with British Steel identified the possibility of using an anaerobic adhesive. Short term tests were favourable and an initial evaluation resulted in the selection of Loctite 638.
Pre-treatment of the pipework involves roughening the surface of the fitting and pipe with emery cloth, after which a ring of retaining adhesive is applied to the fitting and tubing. Once the tube is inserted into the fitting, the joint sets within two minutes, and develops full strength in two to four hours.
In terms of cost, the adhesive retails at US$25 per 5 ml, which corresponds to US$1 per joint. This is considerably cheaper than the cost of alternative assembly approaches.
Lancashire Fittings now recommend adhesives as the first choice for joining stainless steel fittings, as the method is simple and cheap. The company is happy to give a 40 year guarantee for cold water systems, and does not anticipate problems with hot water up to 90°C or cleaning fluids.
The introduction of adhesive bonding has been found to increase the popularity of the fittings, and this has led to higher sales.
Bonded pipework sections are being evaluated as part of a 20 year experiment to prove joint durability. Sections of cold and hot water system within the test installation in a Lancashire Fittings Building are removed at regular intervals for mechanical testing and examination at Leeds University. Currently, performance has been successful for eight years. To assist tradesmen, Lancashire Fittings have produced a pamphlet describing the procedures used for joining their fittings to thin wall tubing.
The excellent integrity of cylindrical joints made using anaerobic retaining adhesives has been illustrated. Other applications for this class of adhesive include bearing retention, automotive transmission components and refrigeration heat exchangers.