Defects of seamless steel pipe pickling

　　In addition to stripping iron oxide scales, hydrogen diffuses into the billet matrix and aggregates at impurities or pores during pickling of seamless steel pipes, resulting in increased internal stress, reduced plasticity and increased brittleness of the steel. This effect is called hydrogen embrittlement. Hydrogen embrittlement is mainly affected by the diffusion rate of hydrogen atoms. The diffusion rate of seamless steel pipe is related to the following factors:

　　1) the diffusion rate of seamless steel pipe in sulfuric acid solution is higher than that in hydrochloric acid solution.

　　2) With the increase of pickling temperature, the diffusion rate of hydrogen increases sharply, but seamless steel pipe with the increase of acid concentration, the diffusion rate of hydrogen does not increase much. Therefore, it is best not to pickle at low temperature and high temperature.

　　3) Some inclusions in pickling, such as arsenic (As), antimony (Sb), hydrogen sulfide (H2S) and sulfur dioxide (SO2), API 5L X46 Seamless Steel Pipe increase the diffusion rate of hydrogen atoms, that is, increase the possibility of hydrogen embrittlement.

　　4) seamless steel pipe of chemical composition of steel also affects the diffusion of hydrogen atoms. The measures to prevent hydrogen embrittlement are to operate according to the prescribed acid concentration and temperature, to shorten the pickling time as far as possible, and to add corrosion inhibitors on time and in quantity.