How to Distinguish the Materials of Seamless Pipes and Galvanized Steel Pipes?

To distinguish the materials of seamless pipes and galvanized steel pipes, it is necessary to observe and judge from multiple angles. Although "galvanizing" is a surface treatment process that can be applied to seamless steel pipes or welded steel pipes, what we usually call "galvanized pipes" refers more to galvanized welded steel pipes. Therefore, the key to distinguishing is to distinguish seamless steel pipes from ordinary galvanized pipes (i.e. galvanized welded steel pipes).
 
Six common methods to distinguish seamless steel pipes and galvanized steel pipes
 
1. Appearance observation
Weld: This is the most direct way to distinguish. As the name suggests, seamless steel pipes have no welds on the surface and are generally circular or in other cross-sectional shapes. Galvanized pipes (usually welded pipes) have obvious welds on the surface. The welds of straight seam welded pipes are linear, and the welds of spiral welded pipes are spiral. This is the simplest and quickest way to distinguish.
Surface state: The surface of seamless steel pipe can be a rough surface after hot rolling, or a smooth surface after cold drawing or cold rolling. The surface of galvanized steel pipe has a zinc layer, showing the unique luster of zinc, and the color is usually silvery white or slightly yellow. The new galvanized steel pipe has a strong luster, which may become dull after a period of use.
Wall thickness: Generally speaking, the wall thickness of welded steel pipes used for galvanizing is relatively thin, while seamless steel pipes can be produced in various wall thickness specifications, including thick-walled pipes, but this is not absolute. There are also cases of galvanized thick-walled seamless pipes, but they are relatively rare.
 
2. Marking and Stamping
Steel stamp: Regular steel pipe manufacturers will roll or spray steel stamps on the surface of steel pipes to indicate the brand (material), specifications, production batch number and other information of the steel pipe. The steel stamp can be used to preliminarily judge the material of the steel pipe. The steel stamp of seamless steel pipes usually includes the material brand, such as 20#, 45#, Q345B, etc., while the mark of galvanized pipes may include the type of galvanizing (such as hot-dip galvanizing or electro-galvanizing) and the implementation standard.
Marking: In addition to steel stamping, some manufacturers will also spray or paste labels on the surface of steel pipes to indicate relevant information.
 
3. Chemical composition analysis (professional method)
The most accurate way to judge the material is to detect the content of various elements in the steel pipe, such as carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), zinc (Zn), etc. through chemical analysis methods.
If zinc is detected, it can be determined that the steel pipe has been galvanized. By analyzing the content of other elements, the material of the steel pipe can be further determined.
Chemical composition analysis requires professional equipment and technicians, and generally needs to be entrusted to a professional testing agency.
 
4. Mechanical properties test (professional method)
Through tensile test, impact test, hardness test and other mechanical performance tests, the yield strength, tensile strength, elongation, impact toughness, hardness and other mechanical performance indicators of steel pipes are tested. Different materials have different mechanical properties. Mechanical properties testing can help determine the material of the steel pipe. Mechanical properties testing also requires professional equipment and technicians, and generally needs to be entrusted to a professional testing agency.
 
5. Magnetic test
Some seamless steel pipes made of stainless steel are non-magnetic, such as austenitic stainless steel (such as 304, 316, etc.) Ordinary seamless steel pipes and galvanized pipes are magnetic and can be simply tested with a magnet. However, it should be noted that some cold-processed austenitic stainless steels may produce weak magnetism, so magnetic testing can only be used as an auxiliary judgment method.
 
6. Spark identification (empirical method, somewhat dangerous, not recommended for non-professionals)
Grinding the steel pipe with a grinding wheel and observing the sparks produced. The spark shapes, colors and quantities produced by steel pipes of different materials are different. Experienced personnel can use spark identification to preliminarily determine the material of the steel pipe, but this requires a wealth of experience and is somewhat dangerous, so it is not recommended for non-professionals to operate.
 
Summarize
 
In practical applications, it is usually necessary to use the above methods in combination to distinguish the materials of seamless steel pipes and galvanized pipes. First, make a preliminary judgment by observing the weld and surface condition. Then check the stamps and markings for more information. If you have any doubts about the material, you can conduct a magnetic test or entrust a professional testing agency to conduct chemical composition analysis and mechanical properties testing. It should be noted that if very precise material identification is required, chemical composition analysis is the most reliable method.