Polyethene Pipes for the Supply of Gaseous Fuels
2001 Edition

Polyethylene compounds used in gas supply pipes must be cadmium-free and free from visible moisture, with certified test results confirming compound classification, physical characteristics, and tensile properties per batch. Long-term hydrostatic strength is verified via a type approval test at 206C over 10,000 hours, with a design coefficient of 2.0. Hydrostatic strength at elevated temperatures requires PE-80 to withstand 4.6 MPa and PE-100 to withstand 5.5 MPa at 806C for 165 hours. Additionally, elongation at break must be at least 350% post-testing, with density and melt flow rate tests aligned with IS and ISO standards. Thermal stability and weather resistance are also mandated to ensure pipe durability.

Pipe outside diameter for sizes up to 25 mm is measured by averaging two Vernier caliper readings taken at 90 degrees, while larger pipes use a flexible Pi tape or circometer with at least 0.1 mm accuracy. Measurements are taken at a distance equal to the greater of one nominal diameter or 300 mm from the pipe end, with pipes conditioned at room temperature before measurement if required. Wall thickness is gauged using dial verniers or ball-ended micrometers, recorded to the nearest 0.1 mm. Tolerances depend on nominal wall thickness, ranging from +0.4 mm for 2.0–3.0 mm thickness to +3.1 mm for 29.0–30.0 mm. Pipe end squareness tolerances vary with outside diameter, for example, 2 mm maximum for diameters 16 to less than 90 mm, increasing up to 7 mm for diameters 315 mm and above.

To ensure long-term hydrostatic strength, the standard mandates several tests: The squeeze-off test involves conditioning the pipe at 06C for at least 10 hours, then compressing the pipe center by a minimum of 30%, maintaining this for 60 minutes, and testing under sustained internal stresses of 4.6 MPa for PE-80 and 5.5 MPa for PE-100 at 806C over 165 hours. Hydrostatic pressure resistance tests are conducted at 806C for 1000 hours every four years and at 206C for 100 hours every two years, using three random samples per pipe size and pressure class. Type tests are performed biannually or when material or process changes occur, with test specimens approximately 200 mm long, marked for axial orientation.

Resistance to gas constituents and environmental factors is assessed through the squeeze-off test, where pipes conditioned at 06C are compressed by at least 30% and held for 60 minutes, then subjected to 806C under specified stresses for 165 hours. Following weathering exposure, test samples from the pipe's outer layer (after removing 0.2 mm) undergo hydrostatic strength testing at 806C for 165 hours, must maintain a minimum elongation at break of 350%, and are evaluated for thermal stability via oxidation induction time (OIT) at 2006C. Additional evaluations include visual inspection, marking validation, pigment dispersion, and periodic hydrostatic testing for both plain and notched pipes, ensuring material integrity over time.

Marking on polyethylene pipes must be permanent, clearly legible, and impressed to a depth not exceeding 0.2 mm to avoid structural damage. Pipes with nominal sizes up to 32 mm require a single marking strip, while larger pipes must have two marking strips on opposite sides. Markings must include manufacturer name or trademark, material grade (PE-80 or PE-100), the IS standard number (IS 14885), nominal diameter, SDR value, pressure rating, manufacture date or batch number, and flow direction if applicable. These markings must remain legible throughout storage, weather exposure, processing, and installation to ensure traceability and quality assurance.