The construction process of galvanized seamless pipe, especially the connection method, is different from that of ordinary galvanized steel pipe. Special attention should be paid to protecting the galvanized layer and avoiding damage to the weld (if any). Although the seamless steel pipe itself has no weld, its galvanized layer still needs to be properly protected during the installation process. The following is a careful summary of the relevant information on the construction process of galvanized seamless pipe.
Characteristics and construction considerations of galvanized seamless pipes
The advantage of galvanized seamless pipe is its excellent corrosion resistance, but the zinc layer is relatively soft and easily damaged during construction. The main construction considerations include:
Galvanized layer protection: Avoid scratching or abrasion of the galvanized layer during transportation, handling and installation. Once the galvanized layer is damaged, the corrosion resistance of the steel pipe will be greatly reduced and it will be prone to rust.
Connection method selection: Welding is not recommended for galvanized steel pipes because welding will burn the zinc layer in the weld and surrounding areas, produce toxic zinc fume, and may cause weld embrittlement.
Cutting and repairing: The pipe ends and damaged parts of the galvanized layer after cutting need to be subjected to secondary anti-corrosion treatment.
Main construction technology (connection method)
There are several main ways to connect galvanized seamless pipes:
1. Threaded Connection
Threaded connection is one of the most commonly used and recommended connection methods for galvanized steel pipes, especially for small diameter pipes.
Process flow:
Threading: Use a threading machine to make standard tapered pipe threads on both ends of the steel pipe. Make sure the pipe end is flat before threading.
Cleaning: Clean burrs and debris inside and outside the pipe mouth, and remove iron filings generated during the threading process.
Anti-corrosion treatment (key step): Since threading will destroy the galvanized layer on the end of the steel pipe and expose the pipe mouth after cutting, the threads and the inside and outside of the pipe mouth must be treated with anti-corrosion. The commonly used method is to apply zinc-rich paint, epoxy zinc yellow primer or other special anti-corrosion coatings.
Connection: Wrap PTFE tape around the threads or apply sealant (such as anaerobic adhesive), then use a pipe wrench to tighten the two steel pipes or fittings.
Inspection: Check whether the threaded connections are tight and leak-free.
Advantages: Quick and easy connection, relatively easy disassembly and maintenance, and adaptable to a wide range of pipe diameters (especially small diameters).
Disadvantages: Relatively low strength, unsuitable for high-pressure or high-vibration applications. The threading process damages the galvanized coating, requiring secondary corrosion protection.
2. Grooved Coupling Connection
Clamp connection (also known as groove connection) is a fast and reliable connection method, especially suitable for medium and large diameter galvanized steel pipes and fire protection pipes.
Process flow:
Grooving/pressing grooving: Use a grooving machine or a grooving machine to press out uniform annular grooves on both ends of the steel pipe.
Anti-corrosion treatment (critical step): Similar to threaded connections, the grooved area and pipe ends also require anti-corrosion treatment to compensate for damage to the galvanized layer.
Install the sealing ring: Put the rubber sealing ring on the joint of the two steel pipes.
Install the clamp: Put the clamp over the outside of the sealing ring, align it with the groove, and tighten it with bolts.
Inspection: Check whether the clamps are installed in place and the bolts are tightened.
Advantages: fast connection speed, easy installation, low technical requirements for workers; has a certain degree of flexibility and can absorb a small amount of thermal expansion and contraction and vibration of the pipeline; good sealing performance.
Disadvantages: Special grooving equipment is required; the groove processing will also damage the galvanized layer, requiring secondary anti-corrosion.
3. Flange Connection
Flange connections are suitable for large-diameter pipelines, parts that require regular disassembly and inspection, and interfaces connecting to other equipment.
Process flow:
Flange installation: Put the flange on the end of the steel pipe.
Flange welding (not recommended for galvanized pipes): Although flanges can be connected to steel pipes by threads or welding, on-site welding of flanges is not recommended for galvanized steel pipes because it will seriously damage the galvanized layer and produce toxic fumes. Galvanized flanges with pre-threaded or special clamp connection interfaces should usually be purchased, or slip-on flanges should be used to allow the steel pipe to pass directly through the flange and flanging it, and then the flanging surface and the flange surface should be sealed.
Sealing gasket: Place a suitable sealing gasket (such as rubber gasket, asbestos gasket, etc.) between the two flanges.
Bolt tightening: Align the flange holes and tighten evenly with bolts and nuts.
Advantages: High connection strength and reliable sealing; easy pipe removal, cleaning, and replacement.
Disadvantages: Complex construction and high cost; requires high flange installation precision.
Other construction precautions
Cutting: Galvanized steel pipes should be cut with a grinding wheel saw or cutting machine to minimize damage to the galvanized layer. After cutting, the pipe ends must be polished and smooth.
Secondary corrosion protection: Any cut surface, thread, groove, or damaged part of the galvanized layer must undergo a thorough secondary corrosion protection treatment. Common methods include applying zinc-rich paint, epoxy anti-corrosion paint, or using a galvanized layer repair agent. This is the key to ensuring the overall corrosion resistance of galvanized steel pipes.
Handling and storage of pipes: Handle with care, avoid dragging and impact, prevent damage to the galvanized layer, keep pipes elevated during storage to avoid direct contact with the ground, and keep them away from moisture and rain.
Pipe supports and hangers: The supports and hangers should avoid direct contact with galvanized steel pipes and should be isolated with insulating gaskets or rubber liners to prevent electrochemical corrosion.
Pressure test: After the pipeline is installed, a water pressure or air pressure test should be carried out in accordance with the specifications to check the sealing of the connection parts.
