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For many years, copper tube has been widely used for water, waste, and vent lines in general plumbing installations. It has been increasingly popular because of its inherent corrosion resistance, economy, and ease of installation using soldered joints. Millions of joints have been made with no difficulty or unsatisfactory service reported. Occasionally, however, a pullout failure or a leak has occurred at a joint. This has been very serious when access for repair was difficult, for example, if it were necessary to break up a concrete slab floor in a home or building or to tear up the pavement in a street. Such infrequent isolated failures are generally considered to be caused by poor workmanship. Recommended practices call for careful cleaning of the tube ends and the fitting prior to soldering, the use of proper temperatures, fluxes, and solders, and suitable methods for applying the heat and feeding the solder. Fittings and tube are made to special tolerances to provide the proper clearance for capillary flow of the solder. It has been observed under carefully controlled laboratory conditions that even an experienced operator will occasionally produce a joint which is not completely filled with solder—that is, a joint of less than maximum strength. The “voids” or unsoldered areas in such joints provide potential sources of leaks. The problem was to determine the factors which result in imperfect or incompletely filled joints. A research program was begun in 1959 by the Solder Joint Subcommittee of the Technical Committee of the Copper and Brass Research Assn. (CABRA) to study the effect of various factors that could have an adverse effect on the quality of soft soldered copper tube joints. The National Bureau of Standards, under the sponsorship of the Copper and Brass Research Assn., some years ago made a comprehensive study of the effect of short- and long-time loading on the strength of joints, over a broad range of temperatures. When this work was reviewed, it was recognized that time, particularly at elevated temperature, could be a major factor in the strength of soldered joints. The presence of arsenic has been known also to prevent the proper adherence of lead-tin alloy coating on copper wire; therefore it was felt that arsenic contamination in soft solders was a possible factor.
Keyes, J. M.
Technical Manager, Division of Calumet & Hecla, Inc., Allen Park, Mich.