Effect of Increasing Thickness of Ship Steel Plate (Continued)

Abstract

In the previous report authors have decided the practical use of 47mm thick ship steel plates, basing on the investigation made from the view point of the performance of the plates and weldment of the upper deck construction of 45, 000 DWT ore and oil carrier.
In this paper we report the result of joinability tests of 40mm and 47mm steel plates when they are welded.
In welding such thick steel plates, the first problem we meet is the crack sensitivity of the weldmeut and the deflection of the welded joints, so for the experiment we selected the following two tests and applied them in equal manner on steel plates of thickness, 25mm, 30mm, 40mm, and 47mm, respectively.
1. Lehigh restraint test (cf. Fig. 2)
2. The measurement test of the deflection of welded joint. (cf. Fig. 3, 4)
By these tests we could obtain each of the following conclusions.
As it may be evid nt, in the joinability of 40mm and 47mm thick plates we noticed a quite different tendency in comparison with that of the plates whose thickness is either 25mm or 30mm.
(1) So far as we make it a problem the crack of the bead of the first layer, the extent of the employment of ilmenite type electrode is restricted according to the thickness of the plate.
In such case if the thikness of plates be 40mm or 47mm, it is very difficult to prevent crack, no matter whether the preheating practice have been applied or not. (cf. Fig. 2)
(2) By using the low hydrogen type electrodes it is very effective in preventing restraint crack even when the thickness of the plates goes up to 47mm. (cf. Fig. 2)
(3) So far as the deflection of the welded joint is made a problem, when the plate thickness is either 25mm or 30mm, the ratio of the depth of the final pass side and backing pass side may be 2: 1(or 7: 3). In this case the deflection is hardly affected by the welding position. (cf. Fig. 6, 7) (4) When the plate thickness is either 40mm or 47mm, the deflection receives a large effect by the welding position. In the case of the butt joints of upper deck assemblies (backing pass side : overhead position, final pass side : flat position) the ratio of the depth is desirable to make 1: 1. (cf. Fig. 5, 6, 7)
Besides, for the supplement (Appendix) we attached the record of welded joint (cf. Fig. I, II, III, IV and Table A) and others (cf. Fig. V, VI).