METHOD STATEMENT UNDER GROUND FIRE FIGHTING WORK

Contents:

1. Objective
2.  Scope
3. References
4. Material
5. Material Procurement, Handling and Storage
6. Trenching & Bedding
7. Backfilling
8. Assembly & Laying
9. BUTT WELD PROCESS
10. Pressure Testing Outside The Trench
11. Testing In The Trench

1. Objective

This method statement provides information concerning the method of construction to ensure compliance with contract requirements, drawing, technical specification and quality control to provide a successful installation, testing, and commissioning of the Installation of U/G HDPE Pipes.

• Scope

HAC shall complete installation of HDPE pipes including excavation and backfilling, testing, witness testing at the site by the engineer, testing and commissioning of the underground fire fighting work.

• References

• Contract Specifications.
• Material Submittal.
• Technical Literature for Manufacturer.
• Design Drawings.
• Shop Drawings.

• Material

• HDPE pipes (HEPEISH)-SDR11-PE100 as per approved one.
• Fittings are HDPE-PE100 (NTG) injection Fittings
• Joints are BUTT welding Joints

• Material Procurement, Handling and Storage

• Upon approval of the material and shop drawing submittals, Contractor shall survey the QTY including fittings as per approved shop drawing and purchase the material as per project schedule.
•   Upon delivery to site, all pipes and fittings shall be stored indoor, in a clean, dry and ventilated place.

• Trenching & Bedding

• Prior to start of excavation, make sure that the pipe line coordinates and elevation has been checked and verified by the surveyor.
• Excavation and sand bedding shall be done mainly by equipments (excavators and loaders).
• Manual excavation is required in cases where equipments are not possible or are not allowed due to safety reasons or where manual excavation is more convenient in a specific area.
• Excavated materials shall be placed at a suitable distance from the edge of excavation so that materials do not fall back into the trench or excavated materials will be put directly to a dump truck and will be unloaded to a designated area away from the trench.
• Loaders shall be used for placing sand bedding materials into the trench while labors will spread manually to meet the correct elevation and slope throughout the trench.
• The minimum trench width from the bottom to 300 mm above the top of the pipe shall be 300 mm for pipe size 90 mm & below and 300 mm + Outside Diameter for pipe size 100 mm & above.
• Depth of trench shall be dug deep enough to provide a ground bed of at least 150 mm from the bottom of the pipe.
• Clean sand bedding layer of 150 mm thickness shall be compacted to at least 70% relative density or 95% Proctor density.
• The trench bottom shall be continuous, smooth, and free of rocks and to the line and grade shown on the approved installation drawings.

• Backfilling

• Make sure that Inspection & Testing has been done and approved before any backfilling works starts.
• Protect top 30 cm of the pipe by backfilling using sand.
• Backfill the remain trench by backfilling material (25 cm max. thickness)
• Backfilling shall be done mainly by equipments (loaders & compactors) while some labors spreading manually the sand and backfill materials wherever required.

• Assembly & Laying
• Before assembly, each pipes and fittings shall be examined from damages.
• Pipe inside surfaces shall be cleaned by rags or by purging air from an air compressor before assembly.
• HDPE piping shall be socket fusion welded in accordance with the manufacturer’s instruction (see attachments) in conjunction with the project specification.
• HDPE piping shall be cut square using pipe cutter or fine toothed hand saw.
• Chamfer or deburr pipe using files or sand papers before jointing.
• HDPE pipes and fittings mating surfaces shall be clean and dry before welding.
• For Underground Piping:
• 250 mm nominal pipe size and less may be assembled next to or in the trench.
• Piping larger than 250 mm nominal pipe size shall be assembled in the trench.
• Crane and (or) labors shall be used for placing pipes into the trench using proper tools and equipments such as ropes, straps and slings to control and maintain proper handling procedure.
• Before start of the pipe laying, the bottom of the trench shall be dry, continuous, smooth, free of rocks and to the line and grade shown on the installation drawings.
• Pipe location, elevation and slope shall be maintained by a surveyor. A survey report shall be made after final installation.
• Sand bags shall be placed at the bottom of pipes to meet the exact elevation and slope of the pipe being installed. The sand bed shall be then adjusted accordingly to maintain the pipe on the ground is on a firm bed for its entire length.
• Excavation a little deeper on the place where the pipe is to be joined shall be done to allow access for the installer for proper joining method.
• Pipe shall be installed continuously downhill without low points and high points.
• Pipe is to be anchored by partial sand covering of the pipe to prevent floatation and to maintain its alignment and level.
• At the end of every work shift, personnel performing the pipe installation shall ensure that the pipe ends are capped to prevent entry of foreign materials.

• BUTT WELD PROCESS
• Butt welding process is a hot-weld type of welding. However, there are technical limitations for both diameter and wall thickness in this kind of linking. Linking by this kind of welding is done from minimum 5 mm wall thickness to 100 mm wall thickness for 50 mm radius to 1600 mm radius.
• During the butt weld process, the pipe butt surfaces are heated by a hot plate until they reach the welding temperature. After the heater plate is removed, the pipe butt surfaces are linked under pressure.
• Equipment Used for Butt Weld, Clamps, Trimming unit, heating unit, Hydraulic unit.
• The following processes are carried out before butt welding:· 
• The temperature of heating unit plates must be checked. 10 minutes stand-by time is required for the heat to be dispersed homogeneously
• The hot plate surface must be cleaned before every process
• The pipes must be fixed vertically and horizontally in the welding machine
• The surfaces of the trimmed pipes to be welded must not be contaminated 
•  Carrying out the Butt Weld Process
•  The environment where the welding will be done must be protected against unfavorable weather conditions (moisture, dust, low temperature, etc). Precautions can be taken such as heating the welding area beforehand or blocking the wind, the welder must be well-trained.
• The pipes to be welded must have the same properties (same type of material, same pressure, same wall thickness).
• Hot plate temperature must be between 200-220oC. Temperature must be checked periodically.
• The pipe butt surfaces must be leaned against the hot plate under low pressure. Heating pressure is kept at P<0,02 N/mm level.
• Heating time is pipe wall thickness x 10 seconds. The thickness that is formed as a result of leaning between hot plate and pipe butt surface under P=0,15  N/mm2 pressure is called lip height.
• Changing time is the time elapsed while the pipe butt surfaces are removed away from hot plate after heating process is over. Without changing time, the hot pipe surfaces get cold and welding quality decreases.
• Linking time, pipe surfaces must be linked in a very short time after changing time is over. The pressure required is P=0,15 ± 0,01 N/mm2. Cooling time under pressure must be kept at the same level under linking pressure cooling time.  

  Table: Base values under 20o ambient temperature 

1. Pressure Testing Outside The Trench
2. If specified by the engineer, pressure testing may be conducted prior to pipe installation.
3.  After the pipe has been joined, fill it with water; carefully bleed off any trapped air.
4. Subject the pipe to a hydrostatic test pressure that is 1.5 times the system design pressure for a maximum of 3 hours. During this time, add water periodically to maintain the test pressure; this compensates for the initial stretching of the pipe. The line pressure tightness is determined by visual observation; therefore, it is not necessary to measure the make-up water.
5. Examine every joint; any leakage must be repaired and then retested.

1. Testing In The Trench:
3. Fill the pipeline with water after it has been laid; bleed off any trapped air.
4. Subject the lowest element in the system to a test pressure that is 1.5 times the design pressure, and check for any leakage.
5. The test procedures consist of two steps; the initial expansion and the test phase. When test pressure is applied to a water filled pipe, the pipe expands. During the initial expansion of the pipe under test, sufficient make-up water must be added to the system at hourly intervals for 3 hours to maintain the test pressure. After about 4 hours, initial expansion should be complete and the actual test can start.
6. When the test is to begin, the pipe is full of water and is subjected to a constant test pressure of 1.5 times the system design pressure. The test phase should not exceed 3 hours, after which time any water deficiency must be replaced and measured. Add and measure the amount of make-up water required to return to the test pressure and compare this to the maximum allowance in the table below.
7. An alternate leakage test consists of maintaining the test pressure (described above) over a period of 4 hours and then dropping the pressure by 10 psi (0.69 MPa). If the pressure then remains within 5% of the target value for 1 hour, this indicates there is no leakage in the system.