220 THE APPLICATION OF ELECTRIC WELDING 



As already stated, the material in the weld appeared to be nearly pure iron, and 

 experiments of repetitive stress show that wrought iron bars are likely to fail under 

 a range of stress of perhaps ±7 to 8 tons as compared with mild steel at ±10 to 11 

 tons. The weld has to be deposited electrically and is subject to variations in work- 

 manship; it would consequently be considered satisfactory if the material could with- 

 stand a range of stress of say ± 65^ tons. 



It would appear to be necessary to design the welded joints in such a manner 

 that the amount of work likely to be thrown on the joint is as small as possible, 

 and to meet such a condition a welded joint requires to be either lapped or strapped. 



Consideration of the dynamic elasticity properties appears to show that in any 

 case the welded material can experience as large a number of repetitions of stress as 

 wrought iron could do, and it is always recognized that, although iron could not ap- 

 proach the tests for mild steel, it was a satisfactory material for shipbuilding 

 purposes. Further, attention to design of details will increase the performance of the 

 welded joint, and in addition it must not be forgotten that 5,000,000 repetitions of 

 stress is perhaps more than equivalent to ten years' good sea service. 



3. Physical Nature and Properties. — It has been mentioned that the welds ex- 

 perimented with are to be regarded as having been produced under most favorable 

 conditions, and that throughout the experimental welds were made with the speci- 

 mens horizontal and below the operator. In practice, welds will require to be made 

 vertically and overhead as well, consequently extreme care will be required in such 

 operations. 



The physical examinations indicate that the materials of the electrode and the 

 system of welding adopted were suitable and reliable. Moreover, there was little ap- 

 parent oxidation and the material in the neighborhood of the weld was not affected 

 to any prejudicial extent. 



4. Strength of Welds and Minor Tests. — Broadly speaking, the tensile strength 

 of butt welds was as great as the unwelded material, but it is considered that greater 

 reliability of workmanship is obtained with joints which are either lapped or strapped. 



It was also found that the lapped joint was practically as strong as a riveted 

 lapped joint and would probably remain tight when subjected to more trying con- 

 ditions than are necessary to disturb a riveted lap joint. 



Lloyd's rules for electrically welded ships. 



It will be seen therefore that the arc-welded joints made by highly skilled work- 

 men with the particular system adopted throughout the foregoing experiments (the 

 quasi arc process, using flux-covered electrodes) proved not only reliable but in some 

 respects superior to the usual riveted joint. 



In view of the satisfactory results of these tests, the Committee of Lloyd's Regis- 

 ter of Shipping has decided that, under certain conditions, electric arc welding may 

 be used in the main structure of a vessel and has adopted, as a tentative measure, 

 the following provisional rules for classification in Llo3''d's Register Book of vessels 

 electrically welded, subject to the notations "Experimental" and "Electrically 

 Welded." 



