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Common Test Methods of Stainless Steel 304 Pipes

Ⅰ. The importance of stainless steel 304 pipes quality


Stainless steel 304 pipes from raw materials to finished products will be used nondestructive testing. Materials such as sorting, size measurement, specific physical and mechanical performance contrast, stress and the dynamic response analysis, internal bad structure or anomaly detection, detection of defects and to give evaluation, which can guarantee the quality of stainless steel 304 pipes, safety and reliability, reduce the manufacturing cost, and enhance the role of economic and social benefits.


Ⅱ. The detection method for stainless steel 304 pipes


In the production of various industrial departments of 304 stainless steel pipe, the commonly used methods are: visual inspection, liquid penetration testing, magnetic powder testing and eddy current testing.


1. Visual detection

Visual inspection is a method to detect defects by observing the surface of stainless steel 304 pipes inspected by the naked eye or by appropriate instruments. The principle of this method is simple, easy to understand and master, and it is not or rarely affected by the material, structure, shape, size and other factors of the stainless steel 304 pipes tested. However, due to the limited ability of human eyes to distinguish, it can only open on the surface of defects and other details.


2. Penetration detection

Osmotic detection is a detection technology based on capillary action principle. In testing, it will be dissolved with fluorescent dyes or colored dye penetrant applied to surface of stainless steel 304 pipes. Due to capillary action, the penetrating fluid will penetrate into the tiny surface defect. Remove excess penetrant, and then apply imaging agent after it is dry. Infiltration liquid of the defects under the action of capillarity is adsorbed to the parts on the surface, which forms the amplified defects, thus detecting the state of the morphology and distribution of defects.


3. Magnetic powder detection

Magnetic particle detection means that after the ferromagnetic material is magnetized, due to the discontinuity on the workpiece, the magnetic field lines on the surface and near the surface of the workpiece will be locally distorted to generate a leakage magnetic field, which will adsorb the magnetic powder applied on the surface. Under proper lighting conditions, visible magnetic marks will be formed, which will show the size, location, shape and severity of the discontinuities.


4. Eddy current testing

Eddy current testing is a nondestructive testing method based on electromagnetic induction. During the test, the stainless steel 304 pipe is put into or close to the coil with alternating current, then the coil produces a time-varying magnetic flux, which can make the tested part induce electromotive force and produce eddy current. If there is a defect in the tested part, the normal flow of eddy current will be changed and the coil impedance or coil voltage will be changed and the corresponding electrical signal can be obtained, thus the amplitude and phase of the signal can be used to determine the existence and extent of the defect.

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