Four quality inspections of stainless steel elbow welding

1. Appearance inspection: Generally, it is mainly observed with the naked eye, sometimes with a magnifying glass 5-20 times. Through visual inspection, surface defects of welded stainless steel elbow welds can be found, such as undercuts, welding tumors, surface cracks, pores, slag inclusions, and weld penetration. The overall dimensions of the weld can also be measured using a weld detector or a template.

2. Non-destructive flaw detection: detection of slag inclusions, pores, cracks, and other defects hidden inside the weld. At present, the most common use is to use X-ray inspection, as well as ultrasonic flaw detection and magnetic flaw detection. X-ray inspection is to use X-rays to take pictures of weld seams, and judge whether there are internal defects, the number and types of defects according to the negative film images. Then evaluate whether the weld is qualified according to the product’s technical requirements. The basic principle of ultrasonic flaw detection is shown in the figure below. The ultrasonic beam is emitted by the probe and transmitted to the metal. When the ultrasonic beam reaches the interface between the metal and the air, it is refracted and passes through the weld. If there is a defect in the weld, the ultrasonic beam is reflected in the probe and accepted, and reflected waves appear on the fluorescent screen. According to the comparison and identification of these reflected waves with normal waves, the size and location of the defect can be determined. Ultrasonic flaw detection is much simpler than X-ray photography, so it is widely used. However, ultrasonic flaw detection often can only make judgments based on operating experience, and cannot leave inspection evidence. Magnetic flaw detection can also be used for internal defects that are not deep from the weld surface and extremely small cracks on the surface.

3. Hydrostatic test and air pressure test: For pressure vessels that require airtightness, a water pressure test and/or an air pressure test must be carried out to check the tightness and pressure-bearing capacity of the weld. The method is to inject 1.25-1.5 times the working pressure of water or gas equal to the working pressure (mostly air) into the container, stay for a certain period, then observe the pressure drop in the container, and observe whether there is any leakage outside, According to these can be assessed whether the weld is qualified.

4. Mechanical performance test of stainless steel elbow: Non-destructive testing can find the inherent defects of the weld, but it cannot explain the mechanical properties of the metal in the heat-affected zone of the weld. Therefore, tensile, impact, bending, and other tests are sometimes performed on the welded joint. These tests are performed with test panels. The test plate used is preferably welded together with the longitudinal seam of the cylinder to ensure consistent construction conditions. The test panels were then subjected to mechanical performance tests. In actual production, this test is generally only carried out on welded joints of new steel types.

Post time: Jun-16-2023