Code of Practice for Laying of Electrically Welded Steel Pipes for Water Supply
1994 Edition

The standard recommends excavating trenches with a minimum width allowing at least 200 mm clearance on either side of the pipe to prevent damage to coatings. The trench bottom must be trimmed to provide a uniform bedding surface. For pipes exceeding 1200 mm in diameter, the bottom curvature should match the pipe's curvature, subtending approximately 120 degrees. If rock or boulders are present, the trench bottom should be excavated 100 mm below the pipe barrel level and filled with lean cement concrete or non-compressible material like sand to create a curved support. Adequate shoring and drainage are essential to maintain a dry and safe trench environment. Additionally, for welding operations within the trench, pits of 600 mm depth and 900 mm length must be excavated around joints to provide sufficient workspace.

Welded joints must be tested following the procedures outlined in IS 3600 (Part 1):1985. At least one test specimen is required for every ten field welds. For pipelines subject to internal pressures exceeding 1.5 N/mm², non-destructive testing methods such as radiographic inspection per IS 4853:1982 or ultrasonic testing as per IS 4260:1986 should be employed, based on agreement between the user and manufacturer. Pressure testing of the pipeline utilizes the highest value among the maximum sustained operating pressure, maximum static pressure, or the sum of static plus surge pressures. The pressure should be incrementally increased at approximately 0.1 N/mm² per minute, with tests lasting at least 24 hours if the pressure is below two-thirds of the design test pressure. Welds not directly pressure tested due to sectional testing must be manufactured with care and monitored throughout commissioning.

For buried steel pipes, appropriate external coatings compliant with IS 10221:1982 are mandatory. These coatings may comprise cementitious, plastic, or other protective materials but do not contribute to the structural strength of the pipe. Above-ground pipelines require protection against atmospheric corrosion through the application of paints, bituminous coatings, or plastic wraps as specified in the code. The selection of coatings must consider environmental conditions and follow modifications outlined in Clause 168.3, aligning with international standards such as BS CP 8010-1981 and BS CP 2010 (Part 2) to ensure durability and protection.

Expansion joints should be installed approximately every 300 meters or at shorter intervals where leakage is unacceptable, positioned between two fixed supports or anchorages. Pipeline installation commences at restrained ends and progresses inward towards the expansion joint which is fitted last. These joints accommodate thermal expansion and contraction through telescopic movement, with some frictional resistance calculated by the formula: F_e = m × d × B × P, where m is the friction coefficient (0.3), d the pipe diameter, B the packing width, and P the internal pressure. Anchorages are installed at strategic points such as valves, blank flanges, tapered sections, and midpoints between expansion joints to resist axial forces arising from hydraulic pressure, friction, and support reactions, thus safeguarding the pipeline from axial stresses.

Following pressure testing, pipelines should be flushed with water at sufficient velocity (typically exceeding 1.5 m/s) to remove debris and foreign materials. Disinfection must be performed using chlorine-based agents such as liquid chlorine, sodium hypochlorite, or calcium hypochlorite, applied through continuous feed or batch chlorination methods. During disinfection, precautions must be taken to avoid contamination sources and prevent backflow of concentrated chlorine solutions. After a contact period of at least 24 hours maintaining a chlorine residual between 2 and 5 mg/L, the pipeline should be flushed until the chlorine residual matches that of the supply system. Bacteriological testing must be conducted to verify disinfection efficacy; if results are unsatisfactory, the process must be repeated until standards are met.