A treatment method for pit defects in continuous rolling carbon steel or low alloy steel pipes

Abstract

The invention discloses a method for treating inner pit defects inside a continuous rolling carbon steel tube or a low-alloy steel tube. The method comprises the following steps: pickling by using an acid liquid which is prepared from the following components in parts by volume for the first time: 10-15 parts of 33% technical hydrochloric acid, 1-3 parts of nitric acid and 20 parts of water, subsequently performing grinding wheel polishing on the continuous rolling carbon steel tube with inner pit defects or inner pit areas of the low-alloy steel tube, and further pickling for a second time by using another acid liquid which is prepared from the following components in parts by volume: 10-15 parts of 33% technical hydrochloric acid and 20 parts of water, wherein the concentration of FeCl2 in the acid liquids for pickling is controlled to be 35-75g / L each time. By adopting the method of twice pickling and once grinding wheel polishing, the inner pit defects distributed in the inner surfaces of the continuous rolling carbon steel tube and the low-alloy steel tube are eliminated, the quality of the inner surfaces of cold-drawn steel tubes is improved, and the purpose of completely eliminating oxidized iron skin on inner surfaces of steel tubes is achieved.

Description

technical field [0001] Embodiments of the present invention relate to the field of metal materials produced in the metallurgical industry, and more specifically, embodiments of the present invention relate to a method for treating pitting defects in continuous rolling carbon steel or low alloy steel pipes. Background technique [0002] Pitting defects in continuous rolling carbon steel or low alloy steel pipes refer to pitting spots in the form of bands or flakes that appear in a certain area on the inner surface of continuous rolling carbon steel or low alloy steel pipes. The occurrence of inner hemp pit defects is mainly related to the scavenging agent used for descaling of the waste pipe. When the scavenging agent with incompatible ingredients and damp agglomeration is sprayed into the inner hole of the capillary, it cannot completely react with the slag, but will form a lump instead. Similarly, when the injection amount of the oxidizing agent is unreasonable, the reactio...

AI Technical Summary

Problems solved by technology

To completely remove the iron oxide scale in the area where the inner hemp pit defect is located, it is necessary to further increase the pickling time, which will cause the following three adverse results: 1. When the iron oxide scale in the area where the inner hemp pit defect is located is cleaned, other parts will appear degree Different over-corrosion phenomena will affect the inner surface quality of the steel pipe after cold drawing

2. Pickling time will be greatly increased

3. Since the surface of the inner hemp pit is covered with the product of incomplete reaction between the oxidizer and the iron oxide scale, crevice corrosion will occur inside the inner hemp pit during pickling, resulting in a significantly accelerated corrosion rate at the bottom of the inner hemp pit, resulting in The depth of the inner hemp pit is significantly deepened, which affects the quality of the inner surface of the steel pipe after cold drawing