First, what are the preparatory steps before detecting the wall thickness of precision steel pipes?
(a) Sample pretreatment: Remove oil, rust, coatings, and other impurities from the steel pipe surface to avoid affecting measurement accuracy. For bent or deformed steel pipes, straightening treatment is required first to ensure that the measurement section is perpendicular to the pipe axis.
(b) Tool calibration:
Mechanical measuring tools: Calibrate with standard gauge blocks to ensure the error is within the allowable range.
Non-destructive testing equipment: Calibrate using standard thickness test blocks, check the deviation between the equipment display value and the standard value, and correct if necessary.
Environmental control: Maintain the testing environment temperature at 20±5℃ to avoid excessively high or low temperatures causing thermal expansion and contraction of the steel pipe, affecting the measurement results; keep away from vibration sources, strong magnetic fields, and other interference factors.
Second, what are the core methods for detecting the wall thickness of precision steel pipes?
(1)Mechanical measurement method: Suitable for precision steel pipes with high accuracy requirements, it is a commonly used arbitration testing method in the industry.
(a) Tool Selection: A wall thickness micrometer is preferred. For large-diameter steel pipes, a combination of an inside gauge and an outside micrometer can be used.
(b) Measurement Procedure:
Select the test sections: Select one section at each end and one in the middle of the steel pipe, for a total of three sections; evenly distribute eight measurement points along the circumference of each section.
Single-point Measurement: Vertically attach the measuring head of the wall thickness micrometer to the inner and outer walls of the steel pipe, ensuring complete contact between the measuring surface and the pipe surface without tilting; when reading the value, keep the line of sight perpendicular to the scale line and record each measurement result.
Repeated Verification: Repeat the measurement three times at each point, and take the average value as the actual wall thickness at that point.
Deviation Calculation: Wall thickness deviation = Actual measured wall thickness – Nominal wall thickness. The result must meet the requirements of relevant standards such as GB/T 3639 and ASTM A1011.
(2)Ultrasonic Testing Method: Suitable for batch testing, scenarios where samples cannot be damaged, or where direct contact with the inner wall of the steel pipe is difficult. The testing accuracy can reach ±0.02mm.
(a) Equipment and Coupling Agent: A digital ultrasonic thickness gauge is used with a coupling agent to ensure no reflection loss of ultrasonic waves between the steel pipe surface and the probe.
(b) Measurement Procedure:
Equipment Calibration: Calibrate the equipment using a standard test block with a similar material and nominal wall thickness to the steel pipe, and set the sound velocity parameters.
Measurement Point Arrangement: Similar to the mechanical measurement method, select 3 cross-sections, with 8 measurement points on each cross-section, avoiding areas with defects such as welds and scratches on the steel pipe.
Data Acquisition: After applying the coupling agent to the probe, press it vertically onto the measurement point. Record the data after the displayed value stabilizes. For measurement points with abnormal values, repeat the measurement and mark them. If necessary, combine with other methods for verification.
Advantages and Precautions: Fast detection speed, non-destructive, and can penetrate coatings; however, it is important to note that the surface roughness of the steel pipe must be ≤Ra3.2μm, otherwise the coupling effect will be affected.
(3) Optical Inspection Method: Suitable for precision steel pipes with ultra-high precision requirements, such as those used in aerospace and high-end machinery.
(a) Equipment Selection: Laser thickness gauge, optical microscope, or X-ray thickness gauge.
(b) Measurement Principle and Procedure:
Laser Thickness Gauge: A laser beam is used to illuminate the outer and inner walls of the steel pipe. The wall thickness is obtained by calculating the time difference of laser reflection. During measurement, the steel pipe must be fixed and stable to avoid vibration.
Optical Microscope: After polishing the steel pipe cross-section, it is placed under a microscope. The wall thickness is directly measured through an image analysis system, allowing for direct observation of wall thickness uniformity.
Applicable Scenarios: High-precision inspection of small-diameter precision steel pipes and thin-walled steel pipes. It can effectively identify problems such as localized wall thickness unevenness and eccentricity.
Third, How to Process and Determine the Wall Thickness Data of Precision Steel Pipes:
Data Statistics: The wall thickness deviation at all measuring points is statistically analyzed. The maximum, minimum, average, and standard deviation are calculated to assess wall thickness uniformity.
Result Determination:
1.If the wall thickness deviation at a single measuring point exceeds the standard allowable range, and the absolute value of the deviation is greater than 8% of the nominal wall thickness, it is considered unqualified.
2.If the difference between the maximum and minimum wall thickness within the same cross-section exceeds 10% of the nominal wall thickness, it is considered uneven wall thickness, requiring further investigation into production process issues.
3. During batch testing, if the percentage of non-conforming test points exceeds 5%, the testing scope needs to be expanded, and full inspection may be necessary.
Fourth, what are the key precautions for wall thickness testing of precision steel pipes?
1. Measuring tools must be calibrated regularly to ensure reliable accuracy.
2. For welded precision steel pipes, two additional test points should be added on each side of the weld. Wall thickness deviation at the weld should be evaluated separately.
3. After testing, a test report must be completed, clearly specifying the steel pipe specifications, material, testing method, test point data, deviation results, and judgment conclusions, for record-keeping and traceability.
Post time: Jan-12-2026