Inspection of steel oil storage tank welds and microcracks primarily focuses on the visual quality of the welds. Inspections typically include weld leg height, undercut, weld distortion, weld bead, arc crater, weld straightness, and other characteristics, as well as the internal quality of the welds, such as slag inclusions, porosity, incomplete penetration, cracks, and lack of fusion. The steps for inspecting steel oil storage tank welds and microcracks are as follows:
Visually inspect the interior and exterior surfaces, welds, and heat-affected zones of the steel oil storage tank to gain a basic understanding of where cracks may exist. Carefully inspect any suspected areas, using a magnifying glass if necessary. Any areas suspected of microcracks should be marked and recorded.
The surface morphology of the steel oil storage tank being inspected directly affects inspection sensitivity, and a clean surface is a prerequisite for effective inspection. Numerous container failure incidents have demonstrated that dangerous defects arising during use are mostly located on the inner surface in contact with the medium. Therefore, any internal medium stains, rust, and scale must be cleaned and inspected by the inspector. 100% magnetic particle inspection can be used. Considering that the welds on the inner and outer surfaces of the gas tank need to be inspected in all positions, including horizontal, horizontal, vertical, and upward, the instrument needs to be calibrated with an A1-30/100 standard test piece before testing. The test piece should be attached to the upward position where the operating conditions are the worst and the detection sensitivity has the greatest impact (such as the upper plate weld in a spherical container and the top weld on the inner surface of a horizontal container) to calibrate the overall performance sensitivity to ensure that no defects are missed. It is worth noting that: for magnetic particle testing of container welds of general media, a water-based magnetic suspension prepared with magnetic paste is usually selected, and the color of the magnetic powder needs to have a large contrast with the surface being inspected. When preparing a water-based magnetic suspension with magnetic paste, it is important to note that: first, mix the magnetic paste with a small amount of water and grind it into a paste, and then add the specified amount of water agent to the gas tank as required. The concentration of the magnetic suspension thus prepared is more uniform, the magnetic powder in the suspension does not clump, and the detection sensitivity is higher. When conducting magnetic particle inspection on containers containing oily media, if the oil film on the weld surface is difficult to remove or fails the water break test, an oil-based magnetic suspension must be used. This should be prepared with high-flash-point, low-concentration kerosene, or a mixture of 50% kerosene and 50% transformer oil. When preparing the oil-based magnetic suspension from magnetic paste, it is important to first mix the paste with a small amount of oil and grind it into a paste, then add the specified amount of oil. For inspecting smooth surfaces or welds in vertical locations, a magnetic suspension prepared with a more viscous oil carrier (such as 30% kerosene and 70% engine oil) should be used to prevent missed defects due to the rapid flow of the magnetic suspension during magnetic particle inspection.
Steel oil storage tank butt welds are subjected to 100% ultrasonic testing or 100% penetrant testing.
Defects (within the welds and microcracks of steel oil storage tanks) discovered using 100% magnetic particle inspection, color flaw detection, 100% ultrasonic testing, or 100% penetrant testing should be re-inspected using radiographic testing to ensure the accuracy of the test results. For suspected cracks discovered using any of the testing methods, a cautious attitude should be maintained and conclusions should not be drawn hastily. Instead, a consultation approach should be adopted, with various testing methods used for further focused review. This also allows for the testing personnel to speak freely, express their opinions on the test results, and pool their wisdom. Through the above work, the location, direction, and burial depth of microcracks in steel oil storage tanks can be determined, and then a repair plan can be determined to ensure the safe operation of the steel oil storage tanks.
