Permissible Water Seepage of Ductile Iron Pipes

When the internal diameter of the pipeline for hydrostatic test is 600mm or larger, the joints at both ends of the test pipe section shall adopt flexible joints. After completion in accordance with Paragraph 2 of Article 9.2.10 of this specification, water injection and pressure supplementation shall be stopped and stabilized for 30 minutes; if the pressure drop does not exceed 70% of the test pressure after 30 minutes, the preliminary test is completed; otherwise, re-inject water to supplement pressure, stabilize for 30 minutes and then observe until the pressure drop does not exceed 70% of the test pressure after 30 minutes. Alternatively, specially made flexible joint blind flanges may be used.

The specifications and installation of equipment and instruments used for hydrostatic test shall comply with the following provisions: When using a spring pressure gauge, during the installation of ductile iron pipes, to insert the spigot into the socket more easily and smoothly, first place the spigot into the socket and press the spigot onto the rubber ring inside the socket, connect the steel wire rope and chain block, and tighten the chain block; until the spigot is fully inserted into the socket, a gap of about 2mm shall be left between the socket and the spigot, and the distance from the outer edge around the socket to the rubber ring shall be consistent.

The accuracy shall not be lower than Class 1.5, and the measuring range should be 1.3～1.5 times the test pressure. Referring to relevant foreign standards, the main purpose of the preliminary test is to check for water leakage, damage, etc. at pipeline joints, fittings, etc. under test pressure; if water leakage or damage is found, the pressure test shall be stopped; and the cause shall be identified and corresponding measures taken before re-testing. The preliminary test is completely necessary to ensure the success of the main test. The nominal diameter of the watch case should not be less than 150mm, calibrated before use and provided with a verification certificate meeting the requirements; the water pump and pressure gauge shall be installed on the branch pipes perpendicular to the pipeline axis at both ends of the test section.

Ductile iron pipe manufacturers produce ductile iron by adding inoculants and nodulizers to ordinary cast iron during pouring. The graphite is vermicular. Although it does not have the obvious defects of graphite structure in gray cast iron and malleable cast iron, due to the long strip and wide thickness characteristics of vermicular graphite, it inevitably splits the matrix structure and causes defects similar to cavities in the structure. Therefore, its performance is slightly higher than that of gray cast iron and malleable cast iron, but lower than that of ductile iron.