China’s seamless pipe network society reports:
For the chemical composition testing of steel pipes, precision pipe is a kind of high-precision steel pipe material after cold drawing or hot rolling.
Because the inner and outer walls of precision steel pipes have no oxide layer, high pressure and no leakage, high precision, high smoothness,
no deformation of cold bending, flaring, flattening and no cracks, magnetic particle detection or penetration testing can effectively find surface cracks, folds and weights.
Surface defects such as skin, hairline, and pinhole.
For ferromagnetic materials, the magnetic particle detection method should be preferred because of its high detection sensitivity; for non-ferromagnetic materials, such as stainless steel seamless steel pipe, the penetration test method is used.
When the cutting margin is reserved at both ends, due to the structure of the detecting device, the ends of the two ends are sometimes not effectively detected, and the tip is the portion most likely to have cracks or other defects. If there is a potential for cracking in the tip, the thermal effects of soldering during installation may also cause potential crack propagation. Therefore, attention should also be paid to the detection of certain areas of seamless steel pipe after welding, and the extension of the end defects of steel pipes should be discovered in time.
For the use of austenitic seamless steel pipes online, when the insulation layer is damaged or there may be rainwater infiltration, the penetration test should be carried out to find defects such as stress corrosion cracking or pitting corrosion.
However, magnetic powder or penetration testing can only detect the outer surface of the steel pipe, and there is nothing to do with the defects on the inner surface. The detection of the inner surface, in particular the detection of crack defects, must be carried out by ultrasonic testing. Therefore, products mainly used to produce pneumatic or hydraulic components, such as cylinders or cylinders, can be seamless tubes or welded tubes. The chemical composition of the precision steel pipe includes carbon C, silicon Si, manganese Mn, sulfur S, phosphorus P, and chromium Cr.
China’s seamless pipe network society reports: the difference between precision tubes and seamless steel tubes
1. The main feature of seamless steel pipe is that it has no welded joint and can withstand large pressure. The product can be a very rough cast or cold-draw.
2. Precision tubes are products that have appeared in recent years, mainly due to strict tolerances and roughness of inner and outer wall sizes.
The main purpose is to judge whether the finished product of the batch meets the product standard of the steel grade, and the result of this analysis is used as the basis for determining the finished pipe of the batch. At present, the Steel Tube Research Institute has completed the large-scale analysis of the chemical composition of the finished tube. The direct use of the direct reading spectrometer and the carbon and sulfur analyzer have completed a large number of production inspection tasks for the online finished tube. The two instruments are now briefly introduced:
Direct Reading Spectrometer
Spectral analysis is a technique for judging the composition of matter by using light emitted by a substance excited by external energy. Its progress is inseparable from the development of physics and chemistry. A substance consists of molecules and atoms and has its properties. By using a property distinction, the components of a substance can be determined. A substance emits a characteristic spectrum under certain conditions, and this property of the spectrum is used to determine the presence of a substance. The measurement results obtained by spectral analysis can only give the type and content of the elements of the substance composition, and cannot show the structure of the substance. Three ways of spectral analysis: linear, banded, and continuous. 188.8.131.52 Characteristics of the spectrum
The direct reading spectrometer is mainly used for C, Si, Mn, P, S, Ni, Cr, Mo, Cu, Al, V, Ti, Nb, B, Zn and five harmful elements (Pb, Sn, As, Sb). , Bi) quantitative analysis tasks, the current instrument for the detection of finished products is ARL4460, this type of analytical instrument has the following characteristics:
1 、High analytical sensitivity, can be used for micro analysis and trace analysis. Instrumental analysis has a relative sensitivity of up to ppm, and instrumental analysis is suitable for micro and trace analysis;
2 、high sensitivity to changes in content;
3、 The light source has good stability and reproducibility;
4 、The line excited by the light source has no background or Beijing is very low;
5、 The results of the analysis are not affected by the different tissue structure of the sample;
6、 Pre-combustion and short exposure time;
7 、The damage to the sample during analysis is small, and the so-called micro-loss or non-destructive analysis is performed;
8 、Fast analysis: Instrument analysis can complete one analysis cycle (about 1 minute) in a short time, suitable for batch analysis and automatic analysis;
9 、Less sample required for analysis: The instrument analysis only needs to be based on the analysis of steel grades, and the selection of suitable steel can be analyzed.
10、 Instrumental analysis is widely used. In addition to the analysis of iron-based samples, nickel-based and chromium-based samples can be tested.
Spectral quantification is a comparative method. The analysis relies on the working curve made by applying the standard sample, and then the content of the unknown sample can be found in the working curve. The standard sample is quite important. Therefore, the following basic requirements must be met:
1、 should have a high degree of uniformity;
2 、The chemical composition should be close to the analytical sample; the structural state should be as close as possible to the structure of the analytical sample; the content range should be slightly larger than the analytical sample to ensure the reliability of the analytical results; there should be a stable state and can be maintained for a long time; The results should be given by several analytical units, preferably with a standard steel with a certificate.