Code of practice for laying asbestos cement pressure pipes
1972 Edition

According to the guidelines, pipes weighing up to 60 kg should be handled manually by two persons using a hand-passing technique. For pipes exceeding 60 kg without mechanical aids, two ropes are used to form loops around the pipe, which is then slid down rigid planks inclined at no more than 45 degrees. Only one pipe should be unloaded at a time, and ropes must be secured on the opposite side to control the descent. Pipes must be inspected during unloading for any visible damage such as cracks or broken edges, and damaged pipes should be segregated for repair or disposal. This approach ensures safe and damage-free handling.

Trenches must be excavated precisely along the required alignment and depth, maintaining a minimum width that provides at least 300 mm clearance on each side of the pipe for jointing. If hard or rocky soil is encountered, the excavation should extend 150 mm below the pipe grade, removing all hard materials and replacing them with fine earth, sand, or fine murum, which must be compacted to form a smooth bedding. For slopes exceeding 30 degrees, pipes must be anchored to prevent movement. These measures guarantee stable bedding and adequate space for pipe installation.

The standard specifies the use of asbestos cement couplings conforming to IS 1592-1970, which feature internally machined ends and incorporate three rubber rings seated in grooves for sealing. The rings are cleaned, lubricated using compatible lubricants, and positioned before assembly, which is performed with a crow-bar or pipe puller. Cast iron fittings are plain-ended to match the pipe diameter and class and are joined using detachable cast iron joints or flange adaptors for flanged specials. Proper lubrication and assembly are critical to ensure leak-tight and durable joints.

Thrust blocks are designed to transfer hydraulic thrust forces generated at pipe fittings to a wider soil bearing area, thereby preventing pipe displacement. They should be located at points of pipeline directional changes, size transitions, pressure line changes, dead ends, and optionally at valves. The design takes into account pipe diameter, operating pressure, fitting type, slope gravity effects, and soil bearing capacity. The required bearing area of the thrust block is calculated by dividing the thrust force by the allowable soil bearing pressure, ensuring soil stresses remain within safe limits.

Pipeline sections must be filled with water either manually or using a low-pressure pump, ensuring all entrapped air is vented from high points to avoid erroneous pressure readings. The test pressure should be 1.5 times the operating pressure but must not exceed maximum values specified in the standard’s pressure class table. Testing should be conducted progressively as installation proceeds to detect any defects early. After successful testing, the trench is refilled, and the pipeline is disinfected prior to commissioning to ensure safety and integrity.