Chemical analysis
Use professional chemical analysis instruments and methods to accurately measure the chemical composition of the pipeline and verify whether the content of various elements meets the requirements and restrictions of API 5L standard for X52 steel grade, such as the content of carbon, silicon, manganese, phosphorus, sulfur and other elements, to ensure that the basic performance of the steel meets the standard.
Tensile test
Test preparation: Cut a sample of appropriate length from the pipeline. Generally, the gauge length and other dimensions of the sample are required to comply with the relevant standards. For example, the gauge length is usually selected to be about 50 mm, and both ends of the sample are processed to ensure that it can be firmly clamped on the test machine.
Test operation: Use professional equipment such as microcomputer-controlled electro-hydraulic servo universal testing machine to clamp the sample on the fixture of the testing machine, and then gradually apply tension until the sample breaks.
Data acquisition and analysis: During the stretching process, stress and strain data are recorded in real time. These data are used to determine important mechanical performance indicators such as yield strength, tensile strength and elongation of the pipe to evaluate whether it meets API 5L X52 Standard requirements.
Flattening test
Specimen selection: Cut a specimen with a length of not less than 10mm but not more than 100mm from a steel pipe that has passed the appearance inspection. Usually, about 40mm is selected, and the edges of the specimen are allowed to be rounded or chamfered by filing or other methods.
Test process: Place the specimen between two parallel plates, and apply uniform pressure to the specimen perpendicular to the longitudinal axis of the tube to flatten it until the distance between the two plates reaches the value specified in the relevant product standards. The speed of the plate movement should not exceed 25mm/min.
Result evaluation: After the flattening test, if no specific requirements are specified, the specimen should be evaluated as qualified if there is no visible crack to the naked eye, and only slight cracks at the edges of the specimen should not be scrapped; if it is a welded steel pipe, the weld position should be placed according to the standard. Generally, if there is no regulation, the weld should be located at 90° to the direction of force.
Water pressure test
Test preparation: Check whether the pressure test equipment is normal, including whether the pressure test pump, pressure gauge, etc. are accurate and reliable, prepare auxiliary tools such as pressure test plugs and water pipes, and ensure that both ends of the pipe body are well sealed.
Test operation: After the steel pipe is filled with water, gradually apply pressure to the specified value through the pressure test pump. Generally, the test pressure is determined according to the calculation formula in the API 5L standard.
Result determination: After keeping the test pressure for a specified time, observe whether the pipe body leaks. If there is no leakage in the pipe body, the pipe is considered to have passed the water pressure test.
Nondestructive testing
Ultrasonic inspection: When ultrasonic waves propagate inside the steel pipe, they will produce reflection, refraction and waveform conversion characteristics when encountering different medium interfaces. The ultrasonic detector receives and analyzes the reflected wave signal to detect whether there are defects such as pores, slag inclusions, cracks, etc. inside the steel pipe. It can detect internal defects of smaller sizes, and has relatively low requirements for the shape and surface of the steel pipe. The detection speed is fast and the efficiency is high.
Magnetic particle inspection: It is suitable for detecting defects on the surface and near the surface of ferromagnetic materials. When there are defects on the surface or near the surface of the steel pipe, it will cause distortion of the magnetic lines of force. By applying magnetic powder on the surface of the steel pipe, the magnetic powder will gather at the defect to form obvious magnetic marks, thereby showing the location and shape of the defect. It is simple to operate and has a low detection cost, but it can only detect ferromagnetic materials, and steel pipes with excessive surface roughness or oil pollution need to be pre-treated.
Radiographic inspection: Using X-rays or γ The rays penetrate the steel pipe, making the film sensitive to light and forming an image. Based on the image, it is judged whether there are defects inside the steel pipe. The shape, size and position of the defects can be intuitively displayed. The detection accuracy of internal defects is high, but the equipment cost is high, the detection speed is slow, and there is a certain radiation hazard to the human body. Corresponding protective measures need to be taken.
Dimension inspection
Use measuring tools such as calipers, micrometers, and calipers to accurately measure the diameter, wall thickness, length and other dimensions of the pipeline to ensure that the size of the pipeline meets the tolerance range specified in the API 5L standard, such as the allowable deviation of the outer diameter and wall thickness, etc., to ensure that the dimensional accuracy of the pipeline meets the use requirements so that it can be correctly connected and installed with other pipe fittings.
