Galvanized Welded Pipe

Galvanized welded pipe refers to a steel pipe product made from straight seam welded steel pipe as the base material, which undergoes hot-dip galvanizing (hot-dip galvanizing) or electro-galvanizing (cold galvanizing) processes to form a zinc alloy coating on its inner and outer surfaces.
Welded steel pipe is made by bending hot-rolled or cold-rolled steel plates or strips and then welding them together with a straight seam on welding equipment. The weld seam is parallel to the longitudinal direction of the steel pipe. Galvanizing straight seam welded pipe significantly increases its corrosion resistance and extends its service life.
Galvanized welded pipe, commonly known as "white pipe," is the most widely used pipe type in the low-pressure fluid transportation field.

The core advantages of galvanized straight seam welded pipe are reflected in the following aspects:
1. Excellent corrosion resistance: The galvanized layer forms a physical barrier and electrochemical protection on the surface of the steel pipe, and its corrosion resistance can reach about 20 times that of ordinary steel pipes.
2. High dimensional accuracy: The outer diameter of the straight seam welded pipe substrate has high accuracy, good ovality, and uniform wall thickness.
3. Lower cost: Compared with seamless steel pipes, straight seam welded pipes have a simpler production process, higher raw material utilization, and obvious overall cost advantages.
4. Complete specifications: From small diameters (4 points, 6 points) to large diameters, it can be produced to meet different engineering needs.

Galvanized straight seam welded pipes are mainly classified into the following categories according to the galvanizing and welding processes:
1. Classification by Galvanizing Process

2. Classification by Welding Process

Galvanized welded pipe production process: Plate detection, milling, pre-bending, forming, pre-welding, inner welding, outer welding, ultrasonic inspection. Hot-dip galvanizing involves first picking the steel pipe to remove iron oxide from its surface. After washing, it is rinsed in an ammonium chloride or zinc chloride aqueous solution, or a mixed ammonium chloride and zinc chloride aqueous solution tank, and then sent to a hot-dip coating tank.

Core Performance Characteristics
1. Excellent Corrosion Resistance: The galvanized layer forms a dual mechanism of physical barrier and electrochemical protection on the steel pipe surface. Hot-dip galvanized steel pipes have zinc coatings on both the inner and outer walls, achieving corrosion resistance approximately 20 times that of ordinary steel pipes.
2. Good Dimensional Accuracy: Welded steel pipes have high precision in the outer diameter of the base material, good ovality, uniform wall thickness, and smooth inner and outer surfaces.
3. Strong Coating Adhesion: Hot-dip galvanizing forms a metallurgically bonded zinc-iron alloy layer with excellent adhesion, verifiable by a copper sulfate test.
4. High Cost-Effectiveness: Compared to seamless steel pipes, welded steel pipes have a simpler production process, higher raw material utilization, and a significant overall cost advantage.
5. Usage Restrictions: Galvanized welded pipes should not be exposed to non-neutral environments such as acids, alkalis, or salts.

Application Range of Galvanized Welded Pipe
Galvanized welded pipe has a wide range of applications, mainly in construction, manufacturing, petrochemical, aviation, automobile, pipeline and other fields.
In the field of construction, it is mainly used to construct building frames and building supports, and can also be used to manufacture regulatory pipelines, water conservancy projects, roof drainage systems, etc.
In the field of manufacturing, it is mainly used to manufacture machinery and equipment, auto parts and heavy machinery parts.
In the aviation field, it is mainly used to manufacture brackets and connectors of aircraft structures.

Galvanized welded pipes combine the dimensional accuracy of welded steel pipes with the excellent corrosion resistance of hot-dip galvanizing, offering up to 20 times the corrosion resistance of ordinary steel pipes. They are widely used in low-pressure fluid transportation, construction scaffolding, fire-fighting pipelines, municipal engineering, and agricultural greenhouses. When purchasing, it is important to distinguish between hot-dip galvanized and cold-dip galvanized pipes, and between galvanized straight seam welded pipes and galvanized seamless pipes, and to select the appropriate material and specifications based on the intended use.

The standard of galvanized welded pipe can vary according to different countries and regions. Production and quality comply with country-specific standards to ensure safety and performance in specific applications. The following are the implementation standards of some common countries:

Chinese standard:
GB/T 3091-2015 "Welded steel pipe for low-pressure fluid transmission", GB/T 13793-2016 "Straight seam electric welded steel pipe", GB/T21835-2008 "Welded steel pipe size and weight per unit length"

British Standard:
BS 1387 "Specifications for heavy and ordinary welded carbon steel pipes", BS EN 10255 "Specifications and grades for non-alloy steel pipe threads and corrosion-resistant coated steel pipes"

American standard:
ASTM A53/A53M Standard Specification for Welded and Seamless Steel Pipe, Black Painted or Hot Dip Galvanized, ASTM A795/A795M Standard Specification for Black Painted or Hot Dip Galvanized Steel Pipe for Fire Protection Service

Japanese standard:
JIS G 3442 "Specifications for Galvanized Steel Pipes"

This standard specifies the classification and code, order content, size, shape, weight and allowable deviation of welded steel pipes, technical requirements, test methods, inspection rules, packaging, signs and quality certificates.

Other relevant standards

The specifications of galvanized welded pipes are expressed in "nominal diameter (DN)" or "outer diameter × wall thickness".

1. Small Diameter Specifications (Nominal Diameter System)
The nominal diameter is an approximation of the inner diameter.

2. Large Diameter Specifications:

Standard wall thickness varies depending on the specification, commonly including DN20×2.75, DN25×3.25, etc.

The lower difference range stipulated by the national standard of galvanized pipe refers to the allowable range of dimensional deviations such as pipe wall thickness, length, and outer diameter. According to national standards, the range of galvanized pipes should meet the following requirements:

Length 3m—16m
Outer diameter 20mm—1680mm;
Wall thickness 0.5mm-30mm;

The length deviation of the galvanized pipe shall not be greater than ±5mm.
The outer diameter deviation should not be greater than ±0.15mm.
The wall thickness deviation shall not be greater than 10% of the pipe wall thickness.

Specifications for allowable deviations in wall thickness of galvanized steel pipes:
1. The deviation level is D1, the allowable deviation of the standardized outer diameter is +1.5%, and the minimum is 0.75mm
2. The deviation level is D2, the allowable deviation of the standardized outer diameter is +1.0%, and the minimum is +0.50mm
3. For D3 deviation level, the allowable deviation of the standardized outer diameter is +0.75%

By controlling the drop range of the galvanized pipe, the dimensional stability and quality reliability of the galvanized pipe can be guaranteed. Therefore, when choosing a galvanized pipe, it is necessary to carefully check whether its size meets the requirements of the national standard to ensure the use effect and safety.