Quality Inspection Measures for Stainless Steel Welded Elbows

In a pipeline system, elbows are used to change the direction of pipes. The most commonly used elbow angles are 45°, 90°, and 180°, although non-standard angles like 60° can be included based on project requirements. Here are the quality inspection methods for stainless steel welded elbows:

1. Non-Destructive Testing:

– Radiographic Testing (X-ray): This method involves using X-rays to create images of the weld seam, helping to identify the presence, size, and type of defects such as inclusions, porosities, and cracks. The evaluation of weld quality is based on the technical requirements of the product.
– Ultrasonic Testing: Ultrasonic testing is based on the principle of sending ultrasonic waves through the material. When ultrasonic waves encounter interfaces between metal and air or other materials, they reflect back to the receiver. The reflected waves are then analyzed to determine the size and location of defects.
– Magnetic Particle Testing: Magnetic particle testing is used to detect surface and near-surface defects and small cracks. It involves creating a magnetic field around the weld area and applying magnetic particles that will accumulate at the defect locations, making them visible.

2. Visual Inspection:

Visual inspection is conducted with the naked eye or using magnification tools such as a 5-20x magnifying glass. It helps identify surface defects on the weld seam of the elbow, including undercut, weld beads, surface cracks, porosities, slag inclusions, and fusion depth. The shape and dimensions of the weld seam can also be measured using welding joint gauges or templates.

3. Mechanical Property Testing of Elbows:

While non-destructive testing can detect defects within the weld seam, it cannot explain the mechanical properties of the base metal within the heat-affected zone. Mechanical property tests such as tensile, impact, and bending tests are carried out on test plates. The tests are preferably performed with the weld joints of test plates aligned with the longitudinal weld of the elbow to ensure consistency with construction conditions. Typically, mechanical property tests are conducted on weld joints of new steel during actual production.

4. Hydrostatic and Pneumatic Testing:

For pressure vessels that require a tight seal, hydrostatic and/or pneumatic tests are necessary to inspect the sealing and pressure-bearing capabilities of the weld seam. In these tests, clean water or gas at a pressure equal to the working pressure (typically air) is introduced into the container at 1.25 to 1.5 times the working pressure. The container is held at pressure for a specified period, and any pressure drop is observed. Leakage from the outside of the container is also checked to evaluate the weld seam’s quality.

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