Pipe Threaded Connections

1. Cut Pipes: Based on the on-site survey sketch, mark the selected pipe materials and cut them according to the lines.

① Cut pipes using a disc saw by placing the pipe on the saw's clamp, aligning it with the marked line, and securely holding it in place for cutting. Apply even pressure on the handle during cutting; avoid excessive force. After cutting, clean the iron film and burrs from the pipe end section thoroughly.

② To cut pipes with a hand saw, securely fasten the pipe material in the pressure clamp of the pressure saw bench, align the saw blade with the marked line, push and pull the saw with both hands, ensuring the saw blade remains perpendicular to the pipe's axis. Apply even force to the push-pull motion, saw all the way through to the bottom, and avoid twisting or bending to prevent deformation of the pipe end surface.

2. Thread cutting: After cutting the pipe material to length, the pipe is threaded in increments based on its diameter. Typically, pipes with diameters of 15-32mm are threaded twice, those of 40-50mm are threaded three times, and pipes over 70mm should be threaded three to four times.

① To thread with a threading machine, clamp the pipe material in the chuck of the threading machine, leaving an appropriate length and then tighten the chuck. Align the board with the threading number, fit the die, position it correctly according to the pipe diameter, secure the trigger, align the lubricant tube with the thread, start the machine, push the plate, and gently release the trigger once the thread reaches the desired length.

② By hand, use a threading die to thread. First, release the fixed trigger, retract the die plate to zero degrees, align the die plate with the sequential number, tighten the die plate, place the pipe material in the pressure table clamp, leaving an appropriate length to secure, gently thread the die plate onto the pipe material, ensuring it is neither too loose nor too tight. Then, push the die plate with both hands, making 2-3 turns, stand to the side and pull the die plate, applying even force. As the threads are about to be completed, gently release the trigger, activate the machine to retract the plate, maintaining the appropriate taper of the threads.

3. Key Assembly: Assemble pipe fittings onto pre-threaded pipe materials based on site sketch measurements.

When fitting pipe fittings, insert the required fitting into the pipe threads and check the tightness (usually hand-tighten for about 3 turns). Apply soldering paste and wrap it with hemp at the thread, then insert the fitting. Use a pipe wrench to tighten the fitting until 2-3 threads are exposed. Remove the hemp, clean off the soldering paste, and label before placing it in an appropriate location for straightening.

Select the appropriate pipe clamp based on the size of the pipe fitting's diameter.

4. Pipe Segment Straightening: Straighten pipe segments that have already been fitted with pipe fittings prior to installation.

① Apply lead oil to the threaded ends of the pipe sections after assembling the fittings. Connect two or more sections, ensuring not to solely focus on the预留口 direction but also consider the pipe's bendability. After aligning properly, turn the预留口 direction to an appropriate position and maintain it straight.

Prior to straightening, after the pipe sections are joined, it is essential to verify the correctness of the pipe diameter,预留口 direction, and changes in diameter as per the design drawings.

③ Place the pipe section on a straightening stand or platform. Typically, two people are needed for the operation: one to visually inspect at the end of the pipe section, and the other to gently tap with a hammer at the bend. Continue tapping and observing until the pipe section is completely straightened. Mark the connection points between the sections, then remove one or more sections and replace them with another until the adjustment is complete.

④ For rigid bends or pipes with larger diameters at the pipe joints, heat the pipes in an oven or with gas welding to 600-800°C (red hot). Place the pipes on a pipe stand and continuously rotate them to utilize their own weight for straightening, or use wood blocks and gently tap with a hammer to straighten the heated sections. After straightening, keep rotating the pipes before cooling. When the temperature reaches an appropriate point, apply oil to the heated areas.

All threaded pipes that have been heated and straightened must be marked with a serial number, then removed to be re-coated with lead oil and wrapped with fibrous material, and finally, the pipe sections are aligned with the mark and tightened.

⑤ When straightening pipeline sections with installed valves, first remove the valve cover, securely pad the valve area, and then strike to prevent cracking the valve body.

Galvanized carbon steel pipes must not be straightened using the heating method.

Do not damage the pipe sections during straightening.

Section II: Pipe Welding

1. Steam pipes with working pressures above 0.1 MPa, heating pipes with diameters over 32 mm, and fire protection pipes in high-rise buildings can be connected using electric or gas welding, as per design specifications.

2. When welding pipelines, wind and snow protection measures should be in place. The welding area's environmental temperature should be below -20°C. The weld joint should be preheated, with a preheating temperature of 100-200°C and a preheating length of 200-250mm.

3. General pipeline welding is done in butt joint style and in teams.

4. Before welding, align the two pipe axes. First, securely weld the ends of the two pipes together. For pipe diameters under 100mm, three spot welds are recommended, while for diameters over 150mm, four spot welds are preferable.

5. For pipes with wall thickness of 5mm or more, the welding ends should be beveled. If gas welding is used to process the pipe bevels, the oxide scale on the bevel surface must be removed, and the unevenness affecting the welding quality should be ground flat.

6. When welding pipe fittings and flanges, first insert the pipe into the flange, pre-weld 2-3 points, then use a protractor to align and level it before welding. Both sides of the flange should be welded, and the weld seam on the inside should not protrude beyond the flange sealing surface.

Section 3: Pipe Flange Connections (require disassembly, connections with equipment valves, etc.)

For pipe sections connected by flange or pipe sections connected with flanged valves, standard flanges must be selected in accordance with design requirements and working pressure.

2. The diameter and length of the flange bolts should meet the specifications. When tightening the flange bolts, they should be tightened symmetrically. The exposed threads of the tightened bolts should be 2-3 turns, not exceeding half the diameter of the bolt.

3. Flange gaskets: For general cold water applications, a 3mm thick rubber pad is typically used. For heating, steam, and domestic hot water pipelines, a 3mm thick asbestos rubber pad should be employed. The gasket must be centered with the pipe diameter and should not be misaligned.

In building water supply systems, copper pipes are commonly used, with primary connection methods being compression fittings and welding.

The sleeve-style connection is convenient and simple to operate. Choosing the correct accessories ensures a tight fit at the connection point, preventing leaks and withstanding sufficient pressure.

The sleeve-style connectors are divided into two types: non-operational type A and operational type B.

A-Type Connector Connection: The installation process involves selecting a sleeve that matches the pipe specifications, cutting the pipe to the correct length, removing all burrs, and inspecting the pipe ends for cleanliness and the presence of deep scratches or other defects. If the pipe end is elliptical, use appropriate tools to round it substantially, then insert the pipe into the sleeve until it reaches the stopper. Tighten the nut using a hand and a wrench until the retaining ring securely clamps the pipe; at this point, the nut on the sleeve cannot be turned by hand. Now, use two wrenches to tighten the bolt an additional 1/3 to 2/3 turn. This allows the retaining ring to bite into the pipe and causes the pipe to undergo a slight deformation.

Operational Connector Type B: This connector can simultaneously clamp both the inner and outer surfaces of the tube, enabling it to both support and securely grip the copper pipe.

Connection methods include verifying the tube specifications and the correct sleeve specifications used, then cutting the tube to the required length with a fine-toothed saw, cleaning the burrs inside and out, fitting the clamp nut and clamp ring onto the tube end, and tapping the corresponding expansion tool or mandrel into the tube end to expand the opening. Next, the solid tube is properly inserted into the tube end and sleeve, and the clamp nut is tightened. First, hand-tighten, then use a wrench to tighten it for about a turn, resulting in a sturdy and airtight joint.

Welding methods primarily consist of two types: soldering and brazing. The main difference between them lies in the different metal fillers, fluxes, and application areas. Professional personnel with the necessary qualifications must operate the welding methods.

Soldering

Ensure that the specifications and dimensions of the pipes and fittings meet the connection requirements prior to the pipe connections.

② Based on the design drawings, the on-site measured pipe length is accurately cut. Cutting can be done using a rotating pipe cutter or a steel saw or electric saw with no fewer than 13 teeth per centimeter, cutting vertically. After cutting, the burrs at the pipe ends should be removed, and the ends should be rounded.

③ The brazing strength is low, and generally, the butt joint form is used for welds. The overlap length is 6 to 8 times the wall thickness of the pipe. When the outer diameter of the pipe is ≤ 28mm, the overlap length is (1.2~1.5)D (mm).

④ Prior to welding, the exterior surface of the copper tube at the welding joint and the interior surface of the fittings should be abraded with fine sandpaper, steel bristles, or abrasive cloth containing other abrasives to remove surface oxides.

⑤ Apply a uniform coating of paste or liquid soldering flux to the exterior surface of the cleaned pipe and the interior surface of the pipe fittings.

⑥ Insert copper tubes into the fittings, push them down until seated and rotate slightly to maintain even gaps, then wipe away excess solder from the extruded joints.

⑦ Apply gas welding flame to uniformly heat the joint until it reaches the soldering temperature.

⑧ To make contact with the heated joint using solder, it indicates that the joint has reached the soldering temperature when the temperature of the copper tube joint allows the solder to melt rapidly. At this point, continue to heat while adding solder until the solder joint is completely filled.

Remove the flame to allow the joint to cool and crystallize in a stationary state.

Clean the residue at the joint thoroughly.

Fifth, Groove-Type Connection (also known as Clamp Connection)

1. Cut steel pipes to the required length using a steel pipe cutting machine, ensuring the cuts are smooth. Any burrs should be flattened using a grinding wheel, resulting in a flat and smooth end face.

2. Press grooves using a groove rolling machine. Mount the steel pipe to be processed with grooves on the groove rolling machine and its tail frame. Adjust the tail frame of the groove rolling machine with a level to ensure it is horizontally aligned with the machine and the steel pipe. Secure the end face of the steel pipe against the end face of the groove wheel stopper on the groove rolling machine, forming a 90-degree angle. Press the grooves in a gradual and continuous manner.

3. Check if the rubber seal is a proper fit, apply lubricant, and place it on the end of one pipe section. Slide the other pipe section over, positioning the seal in the center of the joint.

4. Place the clamp over the rubber ring and secure the edges into the groove.

Step 5: Insert the bolt with the cam into the bolt hole and tighten the nut.

Section 6: Clamp-type Connections

"Cardan Clamp" connections are a type of clamping connection: The end of a "Cardan Clamp" fitting features a socket with a special rubber seal. During installation, the pipe is inserted into the socket fitting until it reaches the locating step, and then a clamping tool is used to clamp the socket area and apply pressure. The rubber seal exerts a sealing function upon being compressed, causing both the fitting and the pipe material to shrink and deform into a hexagonal shape, thereby providing a locating and fixing function, effectively achieving a pipeline connection.