A recent tendency toward production of boilers with greater dimensions has necessitated the corresponding growth in length of the piping in them. In an effort to improve on the conventional type of pipe welding, the writers tried the high frequency induction heating. The present report is an examination of the following conditions encountered in such type of welding: 1) electrical 2) edge figure and inner state of welds 3) gap between heated coils and pipes 4) necessity of reducing materials. The Torikai type impulse high frequency heating apparatus was used with steel pipes, 76 mm o. d., 5 mm thick as specimens. The test results show that 1) so far as the specimens are concerned, operation at 35-40 KW for 50-70 Sec. will be best ; 2) the gap between heating coils and pipes should be 8-10 mm; 3) hydrogen gas is effective as reducing material; and 4) suitability of this method is well confirmed in spite of a considerable variance in mechanical strengths of welds obtained. In conclusion it may be said that this type of pipe welding stands a good chance of being adopted as standard.
The authors mainly studied the X-Ray and the GAMMA-Ray examination from the standpoint of the technique of photography and reached the following conclusion : 1. The 1, 000 KV X-Ray inspection is the most accurate method available of radiographic examination which can increase the efficiency of testing. 2. In regard to detection of defects in weld parts, the GAMMA-Ray examination by radioactive isotope (Co50) seems to make almost no difference compared with the 1, 000 KV X-Ray examination when K" A" or K" M" films are used at about 24" of s. f. d. With the currently available quantity of radioactive isotope, however, a long time of rediation is inevitable.
Heat transferred to the base metal in arc welding was measured by using two plate widths, namely 35 mm and 11 mm, and the writers attempted to separate the heat into two component parts, one being transferred to a comparatively wide surface of the plate, and the other being delivered to the crater. As both the melting speed of welding rod, and the heat absorbed by the base metal are proportional to the welding current, the heat absorbed can be expressed by equivalent voltage. For example, in case of Shinko B-17 welding rod, when the arc voltage is kept 30 V, total heat absorbed by the base metal is 23.5 V (78%) and 18.5 V (62%), width of plate being 35 mm and 11 mm respectively, while heat delivered to the crater was estimated to be about 16.3 V (54%) (See Fig. 11, Fig. 12, Fig. 17.) Some discussions are given on the papers of Rosenthal (1-2) and also Naka (15-17) on the thermal efficiency of welding arc.