Joint Tolerances in Capillary Copper Piping Joints Excessive and non-uniform joint clearance is one of the major causes of poor solder flow BY Ft. B. EDWARDS ABSTRACT. Solderless regions re­ short length at the end of a thin wall shown these solder joints to have garded as defects can be formed in copper tube. The soldering is accom­ broad success in meeting the require­ solder joints in copper piping during plished by capillary filling of the ments for piping systems. fabrication. This study examines fluxed, assembled, and heated joint In 1960, NIBCO began further ex­ typical joints removed from field in­ opening with a molten solder sup­ tensive study of the capillary flow stallations. Principles of capillary plied to the joint edge by hand feed­ solder joint. This continuing research flow are presented to show how sol­ ing. Fittings and tube are made to has contributed to further under­ der flow is related to joint clearance. special tolerances to provide the standing of the joint itself and to the Recommendations are given to pro­ capillary joint clearance suitable for soldering processes associated with mote better filling of joints than is this method of soldering. The tech­ it. shown by the samples examined. nology for these joints in piping was standardized on the basis of inves­ Actual Joints Introduction tigations carried out at the National What is the quality of piping joints Solder joints widely used in copper Bureau of Standards and published piping applications consist of a close by A. Maupin and W. Swanger in 1 MR. EDWARDS is director of research for fitting short sleeve soldered over a 1940. Subsequent experience has NIBCO Inc., Elkhart. Indiana. Fig. 1—Radiograph of ¥4-in. wrought copper elbow, with tracing to show location of regions void of solder in the joint. Defect types are identified by roman numerals I, II, III, and IV WELDING RESEARCH SUPPLEMENT! 321-s as they exist in actual installations? spection technique for these defects, joint soldering tests made by many Long experience has shown that but is, of course, destructive. different investigators, for example field failures are not a common oc­ This miscellaneous collection of Keyes.2 Studies of soldering process currence. But does this mean that all fittings is intended to: (a) represent conditions have revealed many cor­ joints are perfect? Speciment joints some actual plumbing practice, (b) to relations with joint defects. It is im­ (812 joints in 452 fittings) were ob­ indicate at least some of the range of portant to note that all of these de­ tained from scrap yards in Cleveland, joints actually accepted for use and fects are formed by peculiarities of Ohio, Islip, L.I., N.Y., a few from (c) to see what kind of defects might solder flow, or the lack of it, oc­ Osterville, Mass., and a few from be present and common. No attempt curring during the soldering opera­ various other areas of the United was made to select the fittings on tion. Various types of causes for de­ States. Most of the fittings were Vz or the basis of quality, brand, appear­ fects may be described, such as bad % inch size and were reportedly ance, age, original source, size, or cleaning, bad flux, and bad solder, from housing torn down for new specific use. No attempt was made but they all act by influencing the sol­ building or roadway construction. All to trace or date the fittings. They cer­ der flow behavior within the joint to joints were soldered with lead-tin tainly do not represent either all generate a region void of solder. The solder. good or all bad joint making practice. effects of joint dimensional toler­ As far as could be determined, all The sampling of actual solder joining ances are discussed here as causes the fittings had been giving satisfac­ practice represented by the collec­ of defects. tory service prior to their removal. tion is recognized to be limited and The presence of regions void of sol­ suitable only as an indication of prac­ Joint Tolerances der is illustrated in Fig. 1 by a radio­ tice with smaller piping sizes. Joint clearance between the tube graph of a wrought copper ell. A and the sleeve is specified by current tracing showing the void regions is Experimental Joints standards B16.18-1963 for cast given to clarify the x-ray interpre­ The types of defects found in the fittings and B16.22-1963 for tation. All 452 fittings were x-rayed collection have also been found to wrought fittings. Diametral clear­ and the relative filling of joint areas occur frequently in experimental ance is supposed to be no less than was evaluated by viewing the x-ray film. Essentially four kinds of regions unfilled with solder were found. TABLE 1—Types of Defects Present in Sample of Used Joints and Their Distribution by Number and Percent These defects, according to their radiographic appearance, are iden­ Type of defect Number of joints Percentage of sample tified here as: (I) small closed circular I ALL (812) 100% spot, (II) irregular shaped isolated II 328 40.3 closed area, (III) irregular area adjoin­ III 194 23.9 ing a joint edge or another defect re­ IV 232 28.5 gion, (IV) large or extensive area only 183 22.4 usually adjoining an edge of the II only 227 34.1 joint. The types are identified in Fig. III only 87 10.7 1 by their respective numbers. Fre­ IV only 129 15.8 quencies for these types of defects I, II III 33 4.1 I, II IV 29 3.5 are listed in Table 1. I. II III, IV 39 4.8 It is apparent that imperfect joints I, III, IV 35 4.3 are common. In joints that were cut and peeled apart, illustrated by Fig. 2, the closed solderless areas fre­ quently contained solid or semi-solid flux residues and the extensive void areas were frequently untinned. Clearly, all of these defects were formed during soldering of the joint, i.e., none are due to subsequent action on the joint such as corrosion or erosion. There were 550 cast bronze fitting joints and 262 wrought copper fitting joints in the collection. No significant differences with respect to solder fill were attributed to the difference between bronze and copper. X-radiography was used as the pri­ mary means for assessing the solder joint fill. It is a good nondestructive inspection method for this purpose. Ultasonic techniques are capable of detecting unfilled solder areas, but have been limited by manual operation of the test probe to slow examination rates. Cutting and peel­ ing of the joints, with visual or micro­ scopic examination of the opened surfaces, is the most reliable in­ Fig. 2—Cut and peeled joints showing some typical defects 322-s I JUNE 1972 0.002 in. and not more than 0.006 TABLE 2—Diametral Clearances from Standards B16.18-1963 and B16.22-1963 in. for VA in. tubes and varies up to and the Half Maximum Clearance between faying surfaces (Vi Maximum) 0.011 in. for the 8 in. size piping. Standard watertube Diametral clearances, in The minimum and maximum diamet­ size, in. Minimum Maximum Vi Maximum ral clearances for each piping size Vs 0.002 0.006 0.003 are given in Table 2. If the joint parts 1 were geometrically perfect cylindri­ /4 " 0.006 0.003 cal shapes and were assembled cen­ 3/8 " 0.006 0.003 Vi " 0.006 0.003 tered and aligned, joint clearance Ve " 0.006 0.003 would be a concentric uniform gap % " 0.006 0.003 between tube and sleeve. Clearance 1 " 0.007 0.0035 between faying surfaces would thus 114 " 0.007 0.0035 be one-half the diametral clearance Vh " 0.0085 0.00425 value. The values for half the maxi­ n 2 0.0085 0.00425 mum diametral clearances are also 0.0085 0.00425 TA " listed in Table 2. Real joint openings 3 0.0085 0.00425 " usually vary from zero to the maxi­ 31/2 " 0.009 0.0045 4 " 0.009 0.0045 mum diametral clearance because of 5 " 0.009 0.0045 imperfect shape and assembly. 6 " 0.009 0.0045 8 " 0.011 0.0055 Solder Flow Properly cleaned, fluxed, assembled, and heated joints are normally sol­ dered by melting Vs-in. wire solder against the entrance edge of the sleeve member. The solder melts to TABLE 3 Maximum Static Heights for Molten Solder in Capillary Gaps* form a puddle which bridges the cap­ illary gap between the tube and the Parallel plate gap thickness, Maximum molten solder height sleeve. The behavior of the initial d, in. h, in. liquid solder bridge in the capillary 0.001 13.5 space can be visualized as being sim­ .002 6.75 ilar to the behavior of India ink in a .003 4.5 .004 3.37 drafting pen. The liquid drawing pow­ .005 2.7 er of a drafting pen is a function of .006 2.25 the adjusted space between the pen .007 1.93 nibs. If the nibs are adjusted too far .008 1.68 apart, both of them will become wet .009 1.5 with ink, but a liquid bridge will not .010 1.35 form. The beginning of capillary flow .011 1.23 can be observed at the time this .012 1.13 bridge is formed if the pen nibs are .013 1.04 .014 0.97 adjusted to a reasonable spacing. From this liquid bridge an exten­ "Computed using a value of 378 dynes/cm for the interfacial tension of 50-50 sive solder meniscus can develop as solder in contact with flux, 8.89 g/cc for the density of solder, and zero contact more solder is fed and melted.