|
WELDING
The success of electric welding the range of Tubemakers pipes depends upon:
a) correct choice of electrodes
b) adequate preparation of the joint;
c) arc current, arc length and electrode angle;
d) work held firmly while welding
CHOICE OF ELECTRODES
Mild steel electrodes are suitable for welding the Tubemakers range of mild steel galvanised pipes and Galtube* Ultra (thin walled pipe).
Some electrodes are easier to start, have a smoother arc, and an easier slag removal than others. Some electrodes are designed for all positions welding (type 12) while others are more suitable in one direction (type 13). The type of electrode is given by the last two numbers of the code, i.e E4112, E4113.
An ideal electrode for general welding of thin walled pipe and other galvanised products is Austarc 16TC by WIA.
WELD JOINT PREPARATION
The joint preparation determines the ease with which the misfit between two parts can be successfully welded.
NO JOINT PREPARATION
The misfit in the joint is difficult to weld without sacrificing strength. It results in the need to patch up the weld leading to an untidy weld with a high risk of slag inclusion. It usually takes longer to obtain a successful weld.
FLATTENED END
The fit is easier and neater to weld along a flat surface. However, it places all the stresses in a confined area of the joint.
NOTCHED END
This permits a snug fit at the joint with an even gap for welding, making control of the weld metal pool easy with good deposition and a neat appearance.
JOINT CLEANING
Galtube* Ultra does not require the removal of galvanised coating prior to welding. Standard galvanised pipes may need removal of excess zinc around the pipe as galvanising can cause excess spatter. As fumes from welding can be noxious it is recommended that any welding be done in a well ventilated area.
HAND MOVEMENT (Welding Technique)
Thin walled pipe has to be welded with sufficient current (amps) to penetrate, enough weld metal to fill the gap and the correct speed of travel to shape the weld.
Remember when welding thin walled pipe, the side of the pipe is the more difficult area to heat, not the end.
CORRECT CHOICE OF WELDING CURRENT
Too little current:
1. sticking electrode
2. penetration is shallow
3. weld bead rounded
Excess Current
1. melting holes
2. excess spatter
3. overheating electrode
Suggestion: for Galtube* Ultra try 3.2mm electrode at 110-120 amps on high setting.
4 STEP WELDING OF NOTCHED JOINT
STEP 1 Start at top middle, weld across to right and half way down, maintain correct angle of electrode.
STEP 2 Chip slag from the weld of step 1. Restart at top middle and weld half way down left side.
STEPS 3 and 4 Turn the work over and repeat above steps 1 and 2. Remove slag before restarting.
CLEAN UP
Remove slag by chipping and brushing. Paint the welded joint and adjacent heated area with a zinc rich paint, for example, a cold galvanising paint (GALMET) or WATTYL equivalent =Cold Galv.
MIG WELDING
All the above techniques for joint preparation, welding technique and joint protection apply to MIG welding, except for the slag removal.
Galtube* Ultra is easily welded by the MIG process as the galvanising does not affect the weld other than cause spatter to accumulate on the welding shroud. |
