Welding and jointing procedure

Document No.:Page 4 of 4 Date Prepared: 9th May 2007

Revision No. 00 Date Revised:

PVC WELDING, JOINTING AND FRP COATING PROCEDUREPrepared by:

TSK / MQ

Reviewed by:

Unit Manager Maintenance

Approved by:

Technical ManagerPVC Welding and Jointing Procedure

To ensure efficient welding of the fittings to avoid any failure, the following welding and jointing procedure is to be followed:

1. Roughen the surfaces for better adherence. Do this by rubbing the surfaces with coarse emery paper.

2. Thoroughly apply jointing solution to wet both surfaces that will mate.

3. After applying the solution, wait for about 30 seconds so that the solution is partially dry. This will ensure a tight joint. Now slide the surfaces onto each other. When fittings have mated, prepare for welding.

4. For welding, first turn on the PVC welding machine. This will turn on the integrated blower on the machine, which will send high velocity air to the welding gun.

5. Turn open the air valve at the base of the welding gun to set the desired airflow.

6. Next, set the voltage according to the schedule of the fittings that are to be welded. Use the following voltage ranges for common fitting schedules:

a. SCH 10:40-50 V

b. SCH 40:60-80 V

c. SCH 80:80-100V

7. Once the required voltage level has been set, wait for the air heater to raise the temperature of the discharge air to an appropriate level. This takes up about 30 seconds.

8. Check that the discharge air is adequately hot by directing air onto a naked hand. Keep a safe distance (about 10) as the air is hot and may cause a burn.

9. Once the welding equipment has been set up, pick up the filler wire and prepare for welding. The filler wire must be the same material as the base metals.

10. Before welding, preheat the base metals using the hot air from the welding gun.

11. After preheating, start welding by melting the filler wire to fill in the welding groove. Keep a smooth pace; making sure that the base metal is also melted along with the filler wire. This will ensure a strong joint.

12. Continue around the circumference of the fitting, making sure that enough passes are applied so that the weld deposit forms a right-angled triangle.

Reinforcing procedure for welded joints

Use the below described reinforcing procedure to add strength to the joints earlier welded. This will ensure that the joints do not fail when exposed to pressures while in service.

1. Pour polyester resin (Cabasol powder) in a container.

2. Then pour in an adequate amount of epoxy resin. Stir vigorously to form a paste.

3. Pour in 4-5 drops of accelerator (Cobalt). Continue stirring to thoroughly mix.

4. Now pour 4-5 drops of hardener (MEKP Methyl Ethyl Ketone Peroxide). This will harden the paste so that it sets quickly.

5. Now apply the thick paste thus produced onto welded joints.

6. Form a tapered profile to prepare a flat inclined surface where FRP will be later applied.

7. Leave the paste to dry out. This process normally takes about an hour.

8. Now grind off any protrusions and make a smooth surface on which FRP will be applied.

FRP Coating ProcedureUse the following procedure to apply Fiber Reinforced Polyester (FRP) coating to piping. This coating is meant to provide strength to PVC piping.

1. Pour epoxy resin in container.

2. Add 4-5 drops of accelerator (Cobalt) and mix.

3. Pour 4-5 drops of hardener (MEKP Methyl Ethyl Ketone Peroxide) and mix.

4. Now place a woven fiberglass mat on a cardboard / wooden plank.

5. Using a paintbrush, apply the solution made in step 3 to the mat on both its top and bottom side.

6. Place the wet fiberglass mat on the pipe / fitting where it is to be applied.

7. Using a roller set the mat into place.

8. Continue circumferentially and cover the length of the pipe or fitting with these mats.

9. Apply a second coat to add further strength.

10. Now leave the FRP coating to dry out. The drying step can take up to 24 hours depending upon the amount of hardener used.

Fitting A

Fitting B