Butt Welding Procedure: Applicable for Machine Welding

1. Butt Welding Preparations
1. Preparation of welding surfaces:
1. The pipes to be butt-welded should be cut square (perpendicular to the pipe axis). To achieve this correct holding and positioning of the pipe while sawing necessary.
2. Pipe ends should be planed after cutting either by mechanical means or manually using sharp knife.
3. Inspect before welding for damages, wall thickness variation, ovality and cleanlinessof pipe ends surfaces.

The difference in wall thickness of pipes to be welded should not exceed 5% of nominal wall thickness with a maximum of 0.5 mm for pipes upto 200mmOD and 3% with a maximum of 1 mm for pipes upto 400 OD. Follow recommended instructions of pipe and welding machine supplier for 400 OD above pipes.

The maximum permissible ovality in the pipe is 2.5% of pipe outer diam. In case of higher ovality external means should be used to heat up pipe to bring pipe ends ovality in specified range.


2. Heating of Mirrors and temperature control:
1. Check and maintain heating mirror temperature from minimum 190°C to maximum210°C but within ±5°C of the setting . Recommended welding temperature is 200°C.
2. Always keep the mirror surface clean.
3. Protect the heating element from wind, damage and soiling during the intervals between making fusion joint.

The contact surfaces of the heating mirror should be covered with PTFE cloth which is commercially known as “Teflon” PTFE covered mirrors has the advantage that the molten material does not stick to its surface.

The mirror should be provided with a temperature control device so that during welding the surface temperature is automatically maintained within the required limit. Moreover, it is recommended to check the temperature of the mirror before starting heating the pipe ends, by a thermo crayon. An instantaneous change of colour is indication of overheating and a delay in change of colour more than 3 seconds means that insufficient heat has been attained by the mirror.


3. Check Wall Alignment and Gap:
1. The alignment of the two parts should be checked at the same time. In case of mis- matching, a better clamping position is to be sought by rotating pipe etc.


4. laning and Subsequent Checking:
All the pipe ends clamped into the fusion jointing machined are planned. If not it should be planed using planer. After planing the fusion surfaces should not be touched by hands under any circumstances. In case of change ofposition of surfaces the surface must be re-planed.

After planing the pipes should be brought in axial alignment. For this purpose, the prepared of the pipes should be brought in contact with each other ( face to face). The gap, if any, should nowhere round the peripheryexceed the limits recommended by pipe and welding machine supplier.


5. Setting the Fusion Pressure:
1. The specific jointing pressure required for the equalization and fusion can be found in the below table with heating and cooling period. The table lists the times for various wall thicknesses. Interpolate for intermediate values. While calculating the machine pressure it is important to know the cylindrical area.
2. The force needed for the equalization and jointing is given by the product of the fusion area and the specific jointing pressure. This latter force includes the intrinsic resistance of the machine and the resistance of the axially mobile pipe or fitting clamped into (Drag Force). The resistance of longer pipe should be reduced as far as possible by placing the rollers beneath them.
3. Determine the values to be set for equation and jointing on the basis of the information given in table.


2. Butt Welding Operation

1. General:
Before starting the welding operation, the following points have to be taken care of in order to obtain an optimum welding.
1. The two pipes to be butt–welded have to be brought face-to-face to check the alignment.
2. The welder should note down the pressure indicated by the pressure gauge on welding machine, required for the movement of the platform on which pipe is mounted, i.e. to bring the pipes face to face. This pressure should late be added to the required welding pressures. The pressure required for the movement of the platform depends upon the size of the pipe i.e. weight of the pipe and the method of support of the pipe (drag pressure). The As per worldwide practice, the desired pressure to be generated at surface should be 1.5 to 1.8 Kg/cm2 .
3. The pipe surfaces and the welding faces must be cleaned before welding.
4. The hitting mirror must be clean. Any plastic residues or traces of thermo crayon should be removed with clean cloth.


2. Warming –up of pipe ends:
1. The heating mirror should be heated to the nominal temperature of 205°C.
2. The required welding temperature must be checked and having ensured the welding temperature attained by the heating surfaces of the mirror, it is placed between the pipes to be welded. For the proper formation of molten material ring around the periphery of the pipes being heated, the weight of the heating mirror should be taken by the platform of the welding machine.
3. The pipe ends are simultaneously brought in contact with the heating surfaces of the mirror applying initial contact pressure of about 0.4 Kg/cm2 . Then the contact pressure is reduced to about 0.2 Kg/cm2 until proper fusion takes place and a peripheral ring of molten material is clearly visible. This will help a better heat transmission in the pipe wall along axis.


3. Mirror removal:
When sufficient molten material ring around the pipe periphery has been formed, the contact between the fused pipe surfaces and the mirrior is discontinued momentarily for the quick removal of the mirror. Then the plasticized surfaces are immediately brought in contact with each other. The heating mirror must be removed without damage to the welding surfaces .During mirror withdrawal special care should be taken to prevent the welding surfaces from cooling or being contaminated. In the case of bad weather conditions protective measures should be taken. The time of the heating mirror removal should be as short as possible, depending on the welding machine and size of the pipe being welded.


4. Welding of pipe ends:
After removal of mirror, pipes are brought immediately in contact with each other under initial welding pressure of about 0.6 Kg/cm2 and this pressure is gradually raised to 1.5 Kg/cm2 . The pressure must be increased in gradual manner and not like jerk. The pipe welder must also continually watch the formation of the weld bead at the weld line at the beginning should be slowly pushed towards the outside and diminished.


5. Cooling of welded joint:
The weld should be allowed to cool down completely (atmospheric cooling) at the elevated welding pressure and then the welded pipes can be taken out of clamps. It is to be noted that the weld joint should not be subjected to any external stresses for a period of at least twice the welding time. The cooling time depends on the heat input in the pipe for fusion, welding cross-section and the atmospheric temperature.

1. General recommendations for Butt Welding:

The removal of the weld beads is not desirable. If however for special reasons the bead removal is essential it has to be done very carefully so as not to damage the pipe surface.

In case of thick pipe walls it must be remembered that the temperature in the centre may still be high after cooling because of the low thermal conductivity of PE material.

The weld is allowed to get cooled down completely at atmospheric cooling rate. Rapid cooling by water or cloth is not allowed.

2. Recommendations for site conditions for Butt Welding:

The welding machine and accessories should be protected from unfavorable weather conditions such as rain, storm, snow etc. For this purpose a tent or wind –shelter should be used at site.

The place of welding should be spacious enough to accommodate the welding team and the required tools and equipments.

The welding machine and the supports of the pipes must be erected firmly so that they cannot move in any direction during welding. In case of welding on unleveled grounds, the artificial support is recommended to facilitate the welding operation.