![]() ![]() Table 1 Chemical Composition of Stainless Steel Pipe Materials (Mass Fraction (%) Element C Si Mn P S Cr Ni GB/T4237-2015 ≤0.07 ≤0.75 ≤2.00 ≤0.045 ≤0.030 17.50~19.50 8.0~10.5 Base metal 0.07 0.39 0.99 0.033 0.011 17.36 10.14 Weld bead 0.07 0.40 1.00 0.030 0.013 16.85 10.03 (2) Metallographic microscopic analysisįirstly, the specimen was mechanically polished, and the distribution of non-metallic inclusions in the specimen was observed under a microscope without etching. If the content of Cr is low, the corrosion resistance of stainless steel will decrease. It can be seen from Table 1 that the chemical composition of the stainless steel pipe purchased by the company is lower than that of the standard in the base metal and weld metal, and the content of other elements meets the standard requirements.Ĭr is the main corrosion-resistant element in stainless steel. Table 1 shows the chemical composition of base metal and weld of stainless steel pipe. Results and discussion (1) Chemical composition analysis Tear the sample along the crack with hydraulic pliers, scan and observe the crack surface of the sample with Hitachi S-3400 thermal field emission scanning electron microscope, and conduct energy spectrum analysis with EDAX energy spectrometer. Observe the structure of the sample under the metallographic microscope (see Fig. Then, use ferric chloride hydrochloric acid aqueous solution to etch it. Use OLYMPUS-GX51 metallographic microscope to observe the non-metallic inclusions in the sample. The sample includes base metal, weld and heat-affected zone.Ĭarry out pre-grinding, rough grinding, fine grinding and polishing on the sample. (2) Metallographic microscopic analysisĬut the sample from the liquid penetration point (see Fig. Test method (1) Chemical composition analysisĪRL-4460 direct reading spectrometer is used to detect the chemical composition of the base metal and weld of stainless steel pipe to determine whether the chemical composition meets the standard requirements. In order to find out the cause of corrosion cracking failure of stainless steel pipe and avoid the risk of reoccurrence, this article plans to analyze the chemical composition, metallographic microscope and scanning electron microscope of the failed steel pipe, so as to find out the cause of failure and propose preventive measures. 1 Cracking Position and Morphology of Sulfuric Acid Pipe ![]() TDC Flange Forming Machine to Make TDC Flange for Rectangular Duct ConnectionĪccording to the original data, the steel pipe is made of 304 stainless steel, the pipe diameter is DN50, and the wall thickness is 3.5mm.Īfter welding, the penetration test was carried out, and the result was acceptable.Īfter cutting and sampling the steel pipe, it is found that the seepage is located in the weld area and cracks are found.įig. ![]()
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