Abstract
Conical butt joints are one of the most commonly used welded joints in the engineering fields. The quality of conical butt joint is largely dependent on the convexity of the conical butt weld and the difference between the lengths of the two weld toes. To evaluate the convexity and the differences of the weld toes’ length, it would need to undergo destructive testing. In this study, experiment was conducted to measure the convexity and the differences of the weld toes’ length of carbon steel cast and SMAW welded conical butt joint. The experimental results show that the convexity and the differences of the weld toes’ length are within an acceptable range.
Keywords: Conical Butt Joints ; Carbon steel ; SMAW ; Convexity ; weld toes
Introduction
Conical butt joints are usually applied in the engineering field as it provides a neat finish, better mechanical properties and a greater resistance to dynamic loads. The conical shape of the but joints are usually obtained by grinding or machining the surface of the component to be joined. The quality of the conical butt joint highly affect the strength of the joint, and is dependent on the convexity of the weld surface, and the difference between the lengths of the two weld toes. A proper weld convexity is required to generate the enough support and resistance for the load. The difference between the lengths of the two weld toes are very important in order to determine the amount of weld root reinforcement.
In order to evaluate the convexity and the differences of the weld toes’ length of the conical butt joint, destructive testing is required. Destructive testing is a mechanical testing method where the welded joint is physically destructed to assess the joint quality. The destructive testing includes ultrasonic testing, radiography and penetrant testing. However, these method are highly time consuming and costly. Hence, destructive testing requires a proper planning and is only applicable when failure of the welded joint causes drastic consequences. In the past decades, nondestructive testing (NDT) has been introduced as a viable and cheaper option both in terms of time and money. Nondestructive testing is a method that allows for an assessment of properties such as surface integrity of welded joints without destroying the component.
Materials and Experimental Method
The materials used for the experiment are carbon steel base metals, a 7018 carbon steel SMAW rod, a keyhole groove weld and a single pass. The plate of the base material has the dimension of 100 x 50 x 12 mm and the position of the weld is horizontal. The welding rod has an electrode diameter of 3.2mm. The welding process uses the SMAW welding process. The welding is performed by controlling the stick-out distance to be 10mm and using a welding current of 160 A with a welding voltage of 20 V. All of the welding current and voltage was measured using a digital indicator.
The convexity of the conical butt weld and the differences of the weld toe lengths are evaluated by using a Vernier caliper. The Vernier caliper is an accurate measuring device used to measure the convexity of the weld surface and the difference between the lengths of the two weld toes. The vernier caliper is calibrated before each measurement. The vernier caliper is placed at two points, one at the highest point of the convexity and another at the midpoint of the leg lengths on each side of the weld. The distance between those two points is measured using the vernier caliper and recorded. These two measurements are then repeated at least five times and the average of the measurements is calculated. The convexity of the weld is then calculated by subtracting the average distance measured at the midpoint of the leg lengths from the average distance measured at the highest point of the convexity. The difference in the length of the two weld toes are calculated by subtracting the length of one weld toe from the other.
Results and Discussion
The results obtained from the experiment for the convexity and the differences between the weld toes are shown in Table 1. The results obtained from the experiment shows that the convexity of the weld is within an acceptable range, which is from 0.1 to 0.2mm. The difference between the lengths of the two weld toes is also within an acceptable range, which is from 0.3 to 0.4 mm.
Table 1 Convexity and Differences in Weld Toe Lengths
Convexity Difference in Weld Toe Lengths
0.13 ± 0.005 mm 0.35 ± 0.01 mm
Conclusion
The convexity and the differences in weld toe lengths of carbon steel welded conical butt joint seem to satisfy the requirements as stated in the standard. The convexity of the butt joint is within an acceptable range, which is 0.1 to 0.2mm and the difference in weld toe lengths is also within the acceptable range, which is 0.3 to 0.4 mm. It can be concluded that the process of the welding of the carbon steel conical butt joint is successful.
