The following steps are being followed for laying PE pipeline;
1) Route Selection Survey: It is done by the PNG team. Different routes are proposed by this team.
2) Final route selection: Simulation for Network Hydraulics is done in the SYNERGY software. This is basically required to derive the diameter of the pipeline in such a way that the required pressure at all locations can be achieved. Gas supply requirements & Pressure drops are taken into consideration for the best route.
3) Right of Use (ROU): Permission from concerned authorities (Municipal Corporation, Gram Panchayat, State highway authority, etc.) is taken by the ROU department.
4) Route Survey: Marking is done on the final route by the PE-PNG project team of individual GA. Pipe size selection is also determined during the survey. The numbers and locations of SR are also decided by the team.
5) PE Laying: PE Network is divided into two-part,
a) MP (Medium Pressure) Network &
b) LP (Low Pressure) Network.
a) The MP PE network starts from downstream of DRS/CPRS and distributes the Natural Gas till the different Service Regulator located nearby a cluster of domestic customers or a main commercial customer or Industrial Customers up to MRS/IMS. The PE mains are subdivided into sections by means of adequately located manually operated valves (Note: As per PNGRB in MP network minimum one at every 1 Km)
b) The LP Network in PE starts from the downstream of the Service Regulator (SR) and brings natural gas to domestic customers.
c) PE laying process for open cut excavation:
- Trench depth to maintain 1.0-meter cover.
- To check underground utilities with a minimum clearance of 25cm from the PE pipe. If not maintain minimum clearance distance to cover pipe by using RCC half-round / PVC sheet.
- When two PE pipelines (MP & LP) to be laid in the same trench then a minimum 300mm distance to be maintained between two pipes. Also, the MP pipeline is to be laid at Roadside and LP pipeline to be laid at extreme side of the road.
- Pipe laying at the center of the trench for proper sand padding surrounding PE pipes.
- 75 mm sand bedding below pipe in case of normal soil and 150 mm in case of rocky terrain and 75 mm sand padding above the pipe.
- Stone free soil backfilling above sand padding up to 0.5 meters. of PE pipes.
- Laying of Warning tape at 0.5 meters depth from ground level.
- Backfilling entire Trench, Watering and Compaction, Excess soil scrapping.
d) PE Laying Process for Crossing of River/Water Canal/ National Highway / Four-lane state Highway and Railway
- No EF (electrofusion) joints shall be allowed in PE pipes in major crossings as mentioned above. If the pipe diameter requirement is higher than 90mm then the steel pipeline shall be used in major crossings by providing Transition Fittings at both ends.
- 90 mm dia. PE pipes can be used without any EF joint in between if the crossing length is less than 100 meters.
e) Installation of PE valve:
- Isolation valve to be installed at every 1.0 km on a 90mm diameter and above PE pipeline Medium Pressure network. Where tapping of 90mm and above on Medium Pressure PE network is used, PE isolation valve to be provided immediately after tapping.
- Isolation valve to be installed before 2.0 meters of an end cap for 125mm and higher diameter Medium Pressure PE pipeline.
f) PE pipeline marker
Pipeline marker shall be installed at every 200 meters distance on sizes of 63mm diameter and above PE pipelines. Also, pipe line marker shall be installed at both sides of the Main road crossing, river crossing, railway crossing, and any other locations as specified by the entity.
g) Ground connection: Ground Connection required to a joint additional piece of PE pipe as per individual connection. Two-part of PE pipe are joined together through Electrofusion joint.
1. The pipes end to be welded must be cut at a right angle by using proper pipe cutters.
2. Mark the scraping area with an indelible marker pen. The scraping area must be 10mm larger than the insertion depth of the fittings.
3. The oxidized surface is removed from the pipe, by scraping it
4. The scraped surface is cleaned using isopropyl alcohol.
5. The coupler is inserted up to the location mark and the pipe is fastened into the aligning clamp.
6. The plugs are connected to the control unit to the terminals on the fittings and proceed with the set-up of the welding parameters, strictly following the instructions of the welding unit
7. When the fusion cycle is completed, fusion indicators are verified
8. Cooling the joint, in order to avoid possible stresses on the jointing
Transition Fitting Joint: From here Galvanized Iron/ Copper Pipe is jointed with PE Line. RCC Guard is placed on it to protect this joint from external factors.
Industrial Metering Station (IMS)/MRS: They are used to measure the gas supplies to industrial customers. The main components in IMS are a filter, Isolation Valves, RPD Meters, Regulators (if low-pressure requirement) and Non-Return Valve.
Inlet Pressure Range – 1.5 Bar to 4 Bar,
Outlet Pressure – As required by customer.
Main Components of IMS”
- Filter -It is also a cartridge type filter with a pore size of 5 microns.
- Gas meter -Volumetric gas meter is used here mostly RPD meter.
- NRV -It allows one-way flow as discussed above.
- CRV -It is used here to relieve excess pressure in line in case of overpressure.
- PRV in customer premises -Same as PRV in CGS skid, it reduces pressure as required. It operates without a pilot valve.
h) Domestic and Commercial / Non-Commercial PNG Connection
- The connection between consumer meter set assembly and gas appliance may be made by GI Pipes or Copper Tubing or Steel Rubber Hose.
- Commercial Connection has the same components as a domestic connection but some customers may have larger diameter GI Pipeline and higher pressure meter.
- The quantity of gas consumed by an average domestic consumer will remain almost the same for all customers
i) Design of vertical risers: Apartment connections can be classified into the following category:
½‟‟GI pipe riser up to 7 floors for one connection on each floor.
½” GI pipe riser up to 3 floors for two connections on each floor.
1” GI pipe riser for connecting more than seven floors and up to sixteenth floor from single riser & single connection on each floor.
6) Testing of Installed piping connection
|Sr.no,||Type of testing||Test pressure||Test duration|
|1||Pneumatic Pressure test||3.5 kg/cm^2||30 minutes|
|2||Mano-Metric Test||Gas pressure||15 minutes|
|3||Riser PPT||7 kg/cm^2||1 hour|
Pneumatic Pressure Test medium is inert nitrogen/air
- Conversion of Burner: Gas flow rate & pressure are different for LPG & PNG so nozzle sizes are set according to PNG requirement. The jet diameter of 110 mm / 125 mm should be used in PNG.
- Meter Job Card: Meter Job card to be prepared duly signed by Contractor, Customer & Third Party Inspector, and to be submitted to the entity immediately on completion of the conversion.