Effects of Root Opening on Welding Speed, Hardness, Root Penetration and Tensile Strength using E7018 Welding Electrode by Weaving Technique on E250 Plates
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IOE Pulchowk Campus
Abstract
The weldability of E 250 mild steel plates which are extensively used in penstock pipes of
hydropower depends upon different parameters like welding current, voltage, travel speed,
electrode angle and other parameters. Mostly, E7018 electrode is used for welding by
Shielded Metal Arc Welding (SMAW) process. Root opening is the gap between the two
metals in a butt joint that are to be welded. Welding performed in workshops are done in
controlled and qualitative environment but during installation in field due to geological
conditions like high slopes, difficulty in handling pipes in vertical tunnels and inclined
tunnels the welding may not be performed as done in workshop but the design requirement
is same. Four sets of samples are prepared by fitting two samples each of 300 mm length
x 300 mm width x 10 mm thickness with root opening of 2 mm, 4 mm, 6 mm and 8 mm
respectively with bevel angle of 60 degrees, single groove and root face of 2 mm. Welding
has been performed by certified welder, accordance to ASME Section IX, with the use of
E7018 electrode with 2.5 mm diameter by SMAW process and weaving technique.
The welding speed decreased while welding from 2 mm to 8 mm. The welding speed
decreased from 81.31 mm/min to 76.23 mm/min, 66.58 mm/min and 55.54 mm/min at root
opening of 2 mm, 4 mm, 6 mm and 8 mm respectively. Hardness of the material indicates
the changes in property of the material after being welded. The hardness in weld metal
increased from 125.6 HV to 127.3 HV, 136.8 HV and 139.2 HV and hardness in heat
affected zone increased from 104.3 HV to 106.8 HV, 107.7 HV and 108.6 HV at root
opening of 2 mm, 4 mm, 6 mm and 8 mm respectively. Complete root penetration of 10
mm was found while welding in root opening of 4 mm whereas minimum root penetration
of 8.8 mm, 8.1 mm and 6.9 mm was found while welding with root opening of 2 mm, 6
mm and 8 mm respectively. The root penetration decreased with an increase of root
opening. With the increase in root opening, heat input has to be increased. As, the
experiment is carried in constant current and voltage, the heat input required for 6 mm and
8 mm root opening is less causing less root penetration in welds. There is no effect in
minimum required tensile strength of welded zone when welding is performed by E7018
welding electrode in E250 grade materials by weaving technique varying the root opening
from 2 mm to 8 mm. The rupture is found to be in parent metal in all the samples
Description
Welding is the process of joining metals or other materials to form a single set with the
application of heat. Welding is extensively used in production of pressure vessels, pressure
pipes, petroleum storage tanks, petroleum transport pipes, earth moving equipment,
automobiles, turbines. The long route of pipes required for water or petroleum products are
formed by welding the individual pipes. Complex shapes required for specific work are
formed by welding the individual parts