Jointing Manual

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Butt Fusion Welding : Ref IS7634 Part 2 2012.

Butt Welding Procedure : Applicable for Hydraulic welding machine preferably with data logger to record the parameters of fusion welding

  1. Preparation of welding surface :
    1. The pipes to be welded should be cut square;
    2. Pipe ends should be planed after cutting;
    3. Inspect before welding for damages, wall thickness variation, ovality and cleanliness of pipe ends surfaces.
    4. Re-rounding tools shall be use specially for the coils to prepare the pipe ends ready for fusion jointing.
  2. Heating Mirrors :
    1. Check and maintain heating mirror temperature from minimum 190 deg C to maximum 210 deg C but within +/- 5 deg C of the setting. The temperature indicator must be in valid calibrated condition.
    2. Always keep the mirror surface clean.
    3. Protect the heating element from wind, damage and soiling during the intervals between making fusion joints.
  3. Check Wall Alignment and Gap
    1. The alignment of the two parts should be checked at the same time. In case of mismatching , a better clamping position is to be sought by rotating pipe etc.
  4. Planning and Subsequent Checking
    1. All the components clamped into the fusion jointing machine are planed .If not it should be planned using planer. After planing the fusion surfaces should not be touched by hands under any circumstances. In case of change of position of surfaces the surface must be re-planed.
  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 time for various wall thicknesses. Interpolate for intermediate values.
    2. The force needed for the equalization and jointing is given by the product of the fusion area and the specific jointing pressure. The force required to move the pipe must be added to this. This latter force includes the intrinsic resistance of the machine and the resistance of the axially mobile pipe or fitting clamped in it (Drag Force ) .The resistance of longer pipes 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 the table.
  6. Fusion Jointing Procedure :
    1. After attaining the fusion temperature , position the heating element in the fusion jointing machine. Press the parts to be jointed against the heating element with the force required for equalization until the entire circumference of each jointing face rests completely against it and a bead has formed. Reduce the equalization pressure almost to 0.The heating time listed in the table is measured from this movement. No external lubrication adhesives, jointing solutions have to be used in this process.
    2. Once the heating period has lapsed , remove the parts from the heating element which should be removed without touching the jointing surfaces and push the parts together immediately. The changeover time must not exceed the values listed in the table. Precaution should be taken during jointing that the parts removed together swiftly the surfaces are about to touch.
    3. The welding surfaces should be moved together so that they are in contact along the entire circumference. Next the pressure should be increased rapidly to the present jointing pressure within the period of time specified in the table. This pressure should be maintained during the entire cooling period.
    4. The jointed parts must stay in the fusion jointing machine under jointing pressure until the end of the cooling period specified in the table.

Note :

In case of hand welding ( usually preferred for the sizes below 90 mm ) , the pressure vs time diagram will be followed; however instead of machine , it will be done manually through skilled technicians.

Visual Inspection :

All the joints will be visually inspected for the alignment and perfectness of the bid. The bead should form around the entire circumference of the pipe.

Field Hydro Testing :

  1. All pipe work, fittings and appliances shall be inspected and tested hydraulically after the completion of installation. Before starting any test the system shall be visually inspected to ensure that the recommendations for the correct installation procedure have been complied with and that the pipeline together with appliances, valves and fittings are laid in the prescribed manner.
  2. All control valves shall be positioned “Open” for the duration of the test and open ends temporarily closed with water-tight fittings. The testing pressure should not be less than one and half times the rated pressure of the pipe under use.
  3. Polyethylene pipelines shall be pressure tested at ambient temperature. After filling with water the pipeline shall be left to stabilize for a period of 1 h.
  4. Fusion joints may be covered during testing. Flanged joints shall be kept open for visual inspection. The pipeline shall be filled with water and pressure tested from the lowest point.
  5. During the test period, make-up water is continuously added to maintain the pressure.
  6. Under no circumstance, air is to be used instead of water for testing.
  7. Tests should be performed on reasonable lengths of pipelines. Long lengths more than 2 000 m may make leak detection more difficult.
  8. If the test is not complete because of leakage or equipment failures, the test section shall be depressurized and allowed to relax for at least 8 h, before starting the next testing sequence.
  9. Testing outside the trench is to be avoided, as pipe rupture may involve safety issues.
  10. Pressure should be applied either by hand pump or power driven pump.Pressure gauges should be correctly positioned and closely observed to ensure that at no time are the test pressures exceeded. The system should be slowly and carefully filled with water, to avoid surge pressure of water hammer. Air vents should be open at all high points so that air may be expelled from the system during filling.
  11. When the system has been fully charged with water and air displaced from the line, air vents should be closed and the line initially inspected for seepage at joints and the firmness of support under load. Pressure then may be applied until the required test pressure is reached.
  12. Acceptance Criteria : After attaining the steady test pressure of 1.5 times the rated pressure of , the pipeline shall be tested for one hour test duration. The test pressure should not fall more than 5%. end of one & half hour duration.