Key Points of Pipeline Engineering Construction

Pipeline engineering is a comprehensive project that applies a variety of modern scientific and technological methods. It includes a large number of general construction and installation projects, as well as some professional engineering buildings, professional equipment and construction technologies. Today we have summarized the key points of pipeline engineering construction. Let's take a look.

Pipeline network connection

Flange connection

(1) The diameter and length of the connecting bolts should meet the requirements of the specifications. After the bolts are tightened, the exposed threads should be 2 to 3 threads and should not be greater than 1/2 of the bolt diameter.

(2) When tightening the bolts with hydraulic or pneumatic tools, be careful not to exceed the specified torque.

(3) To avoid adhesion between the gasket and the thread when tightening the bolts and nuts at high temperatures, apply anti-sticking agent to the threaded parts during operation.

(4) For high-temperature valves above 300°C, the flange connection bolts, valve cover tightening bolts, pressure seals and packing gland bolts must be tightened again after the temperature rises.

Welding

(1) When the ambient temperature of the welding area is lower than -20℃, the weld should be preheated, the residual heat temperature should be between 100 and 200℃, and the length should be between 200 and 250mm.

(2) When the wall thickness of the pipe is greater than 5mm, the weld should be beveled. If the pipe bevel is processed by gas welding, the oxide layer on the surface of the bevel should be removed and the uneven parts should be smoothed.

(3) The electrode coating should not fall off or have obvious cracks. It should be dried at 350~400℃, and the drying should not exceed 2 times.

(4) When welding multiple layers, the root of the first layer of weld should be welded through and should not be burned through; the thickness of each layer of weld should be 0.8~1.2 times the diameter of the electrode, and the arc starting point and arc extinction point of each layer should be staggered; the starting point of the weld between adjacent layers should be staggered by 20~30mm.

(5) The number of times an unqualified weld should be repaired should not exceed 3 times.

Socket-and-spigot connection

(1) Note that the pipe spigot should be in the downstream direction and the socket should be in the reverse direction.

(2) The protruding mortar parts squeezed out during the installation of the two pipe interfaces must be dealt with in a timely manner. The protruding mortar can be smoothed by pulling straw bags, or a smaller worker can be sent into the pipe to smooth the mortar, fill the loose joints with mortar, and remove the debris in the pipe.

Clip-type connection

(1) When connecting pipes, ensure that the pipe deformation margin is sufficient to prevent damage caused by tensile stress; avoid multiple disassembly to ensure the sealing effect of the pipe.

(2) When connecting pipes, excessive lateral force will lead to poor sealing, so it should be avoided that it is subjected to lateral force.

(3) Fillers such as sealants shall not be added to improve the sealing performance. If the sealant is flushed into the hydraulic system, the damping hole of the hydraulic component will be blocked.

Groove connection

(1) The appearance of large-diameter clamps should be sampled and inspected to ensure its accuracy. The inspection contents include: 1) Whether the diameter of the circle on the flexible clamp plate is too large or too small, whether the gap between the two clamps is about 2mm, and whether the out-of-roundness exceeds the standard; 2) Whether the flange height and thickness of each clamp inserted into the groove meet the requirements; 3) Whether the radial deformation of each clamp exceeds the standard.

(2) When installing the clamp, attention should be paid to the pipe material, external dimensions, pipe mouth deformation size, groove quality and clamp quality, and size deviation size, and each clamp must be fully inserted into the groove.

Pipeline connection

New pipeline positioning

Before positioning the new pipeline, the specific location of the old pipeline must be found out, and try not to occupy the original location of the old pipeline (it is best to ensure that the net distance between the new and old pipelines is more than 1.5m). This ensures that the old pipeline can supply water normally until the connection to the user is completed, and then the old pipeline is completely abolished. However, in the old urban area, if the planned location has been occupied by various underground pipelines, there is no other suitable location for the new pipeline, and it has to occupy the original location of the old pipeline, then temporary water supply measures must be taken.

Construction principles

(1) Connect large users first, then small users. First connect the branch lines of large water users (daily water consumption greater than 500m³), and then connect the branch lines of small users. This can minimize the losses caused by water outage and reduce the impact.

(2) Connect key users first, then general users. For some users with greater impact from water outage (such as hospitals, schools, key factories and mines, etc.), the household pipes should be connected first to restore water supply as soon as possible, while for general users with less impact from water outage, the work can be delayed as appropriate.

(3) Connect the easy first, then the difficult. For users with less construction difficulty, the branch lines can be connected in advance, while for branches with more construction difficulty due to other issues such as unknown pipeline location and burial depth or obstruction by other surrounding underground facilities (such as drainage pipes, cables, etc.), they can be concentrated at the end and solved at once.

Water-tightness test

The water-tightness test of drainage pipes is a comprehensive inspection of construction quality. The main reasons for failure of the water-tightness test are as follows.

(1) The drainage pipe itself is of substandard quality, causing leakage during the closed water test;

(2) The uneven settlement of the pipe foundation causes cracks in the pipe interface and leakage;

(3) Water seepage occurs in the inspection well;

(4) The sealing of both ends of the pipe is not tight enough during the test.

Key points for pipeline leakage prevention

(1) If the concrete construction joint is not properly left or cleaned, it will cause concrete seepage.

(2) Leave the construction joint at the specified position and add water stop strips inside it. It should be noted that the construction joint should not be left in the weak waterproof parts and the bottom plate in principle; leave the construction joint on the wall board, and try to make it consistent with the deformation joint. A special person should be assigned to clean the construction joint and check it to eliminate hidden dangers.

(3) Before pouring, a special test for the preparation of impermeable concrete should be carried out to determine the mix ratio; coarse and fine aggregates can also be used to prepare concrete in two levels to enhance the impermeability; after the concrete is poured, it must be cured within 12 hours, and covered and watered during final setting. Strengthen water replenishment in summer and insulation in winter.

(4) If the embedded parts are not properly treated, leakage may occur. Attention should be paid to strengthening the vibration of the concrete around the embedded parts and strengthening the fixing of the embedded parts; flexible connection water stop sleeves should be installed for through-wall pipes.

(5) Before the waterproof coating is applied, it is necessary to ensure that the strength of the base layer meets the requirements and the surface is clean and tidy. When applying, it is advisable to apply vertically first and then horizontally, and first the details and then the whole. After the waterproof coating is cured and dried, the waterproof membrane can be laid, and the joints can be sealed and strengthened with adhesive tape and sealing materials.

(6) The incomplete weld of the water stop plate of the through-wall bolt is very likely to cause leakage. When supporting the formwork, the water stop plate should be fully welded on both sides of the through-wall bolt, and a water test should be carried out; after removing the formwork, waterproof cement mortar should be used to seal the mouth.