The Welding Procedure for the Large Thick Plates of Upper Deck Construction Welding Carried Out to Actual Ship Steel Results of Plates of 45,000 DWT Ore and Oil Carrier

Abstract

It was only recently that the A.B. specification was established for ship structure steel plates up to 50 mm thick plate and there are many problems yet to be solved in connection with the use of such extra wide size plates in the actual constructions of mammoth vessels, such as the 65,000 or 100,000 DWT tankers which will be built in near future. However, at the time when only the plates thinner than 38 mm (1^1/2") in A.B. rule had been specified, there occurred a case, in which 47 mm thick steel plates were applied for almost all the upper deck constructions in shipbuilding as mentioned below. In the previous papers, authors reported their decision for the practical use of 47 mm thick steel plates in the upper deck construction of 45,000 DWT ore and oil carriers, basing on the investigations made from the view points of both the performances and the procedures of their welded joints. After such decision, three actual ships have been built, in which investigations were made to confirm their previous conclusions on the following items : (1) The mechanical and impact tests of the ship steels to ensure their performance in the case of normalized plate of extra wide size. (2) The non-destructive inspection of the welded joints by radiographic technique to ensure the result of preventing restraint crack by the welding procedure based upon Lehigh restraint test. (3) The measurement of the deflection of the welded joints. In this paper, authors have obtained the results of these investigations, which are summarized as follows : 1. It is generally possible that the commercial 47 mm thick ship steel plates in the condition of fully killed and normalized have sufficient notch toughnesses as expected. However, care should be taken in their heat treatments, sush as normalizing to prevent lack of tougbness and in the actual ships 8% of the plates show such lower specific absorbed energies of V-Charpy impact tests at 0℃ as from 3.0 to 6.0 kg-m/cm^2. On account of this steel arrangement in actual ships should be so arranged, following the results of material tests in steel manufacturer, that higher ductile plates would be occupied the part of ship where high stress conditions would occur. 2. No problem, such as cracking, has been caused in the actual welded joints by the proper procedures decided following the preliminary test results. 3. In order to minimize the angular distortion of the welded joints it is better to use symmetrical double Vee groove edge preparations and apply proper prespringings by restraint jigs.