In addition to anticorrosion, the municipal water supply pipeline and
spiral steel pipe need internal anticorrosion treatment. At that time, most cement mortar fabrics were used for anticorrosion treatment. The method was to uniformly spread a layer of cement mortar on the steel pipe wall and protect it from the pipeline. The cement mortar in the coating can not only avoid the corrosion of the inner wall of the pipeline, prolong the service life of the pipeline, protect the water quality, adhere to or improve the water supply of the pipeline, and have obvious economic and social benefits.
The common knowledge of spiral steel pipe in making cement mortar inside the coating is as follows:
(1) the need for spiral steel pipe material
Cement should be used over 42.5 grade silicate, usually Portland cement or slag Portland cement. Sand should be used to consolidate, clean, have good natural sand and no sundries. The fuzzy quantity is not more than 2%, the maximum size is not more than 1.2 mm. The gradient should be determined according to the construction technology, diameter and site construction conditions. Mixed water is essential for cleanliness, and does not possess the strength of soil cement, acid, alkali and other cement mortars, and the durability of materials, usually using drinking water.
(2) construction conditions of spiral steel tube coating
The construction of cement mortar fabric should be completed under the pipeline, and the test pressure should be compacted and compacted according to the planning needs. During the construction of the fabric, the pipeline must be in a stable state. If the first layer of fabric is treated with the next layer of anticorrosion, the tube wall will be thinner, the stiffness is small, and the soil will be hoisted during construction, and the soil will also deform and destroy the coating during transportation. Before the construction of the fabric, the inner wall of the pipe must be cleaned to remove soft oxides, rust, dirt, grease, welding slag and other accessories; the penetration of the steel tube wall must not be greater than the 1/3 of the coating program; the vertical deformation shall not exceed the planning rule and should not exceed 2% of the pipe diameter.
(3) construction of spiral steel tube coating
Cement mortar spraying can be constructed by mechanical spraying, manual pressure relief, drum drumming or centrifugal precasting. If the internal coating is to be made by precast method, the spiral steel pipe should be used for transportation, installation and backfilling to protect the protective coating. In construction, the main mixing cement mortar, cement sand quality mix ratio is 1: (1-2), cement mortar slump of 60-80mm, cement mortar compressive strength should not be less than 30MPa. The inner surface of cement mortar with mechanical coating method is smooth and delicate, with uniform thickness and good effect. Foreign countries began to use mechanical spraying construction in 1930s. Since 60s, China has successively built in cities such as Shanghai, Qingdao and Dalian. When mechanical spraying is applied, elbow, three way, special pipe, gate valve near pipe section, etc. can be smeared with hands, and the smooth split section is connected with the mechanical spray cloth. In addition, towels or centrifuge prefabrication methods are widely used. No matter what construction method is adopted, the protection technology of spiral steel pipe is the key link to ensure that the cement mortar coating does not crack and hollowing. Therefore, after the inner coating of cement mortar is formed, the pipe should be blocked immediately and the air convection is not formed. After the condensation of water, the protection time of Portland cement should not be less than 7d, and the slag cement should not be less than 14 d; the water should continue to keep wet before the water should be blocked.
(4) construction quality of spiral steel tube coating
The quality of coating in cement mortar shall meet the following requirements.
1) crack width should not exceed 0.8mm, not longer than pipe length, and should not be greater than 2.0m.
2) the thickness error and pitting of the coating, the surface defects such as empty points should conform to the depth of the rules, and the defect area of the spiral steel pipe should not exceed 5cm2.
3) the flatness needs a gauge of 300 millimeters long. The gap between the coating surface and the ruler should be less than 2mm along the vertical axis of the tube wall.
4) the hollow area of every 1 square meters should not exceed 2 square meters, and not more than 100 square centimeters per square metre.
