JP2007105574A - Local corrosion-control method of steel pipe inner surface in steel pipe manufacturing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of preventing a local corrosion of a steel pipe inner surface in a steel pipe manufacturing process. <P>SOLUTION: The Method of preventing the local corrosion of the steel pipe inner surface in the steel pipe manufacturing process comprises the local corrosion-control method of the steel pipe inner surface in the steel pipe manufacturing process characterized by the following. A steel pipe is cut to 7,000 mm or less immediately after a cold work; the steel pipe inner surface is air-blown; after a keeping inclination angle of the steel pipe being held to 1° or more, a dipping to a degreasing liquid is carried out 4 times or more; and a processing oil supplied to the steel pipe inner surface in cold-working is degreased. Thus, the processing oil of the steel pipe inner surface after the degreasing process can be completely removed to prevent the local corrosion of the steel pipe inner surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for preventing local corrosion on the inner surface of a steel pipe in a steel pipe manufacturing process.

  Conventionally, in a steel pipe manufacturing process, local rust may be generated on the inner surface of a steel pipe with a small diameter pipe having an inner diameter of approximately φ30 or less, and internal flaws due to corrosion have occurred from this. In particular, the cold pilger manufacturing process involves cold rolling, degreasing, annealing, straightening, cutting and edge treatment, and pickling. It was not specified what caused this to occur.

  On the other hand, in cold pilger rolling, the hot-rolled base metal is cold-rolled to reduce the wall thickness and outer diameter, and the wall thickness is inserted into the inner diameter side of the main pipe to finish the target product. It is determined by the mandrel made and finished as a product. In such rolling, since it is rolled in the cold, heat generated by processing heat and friction is generated between the mandrel and the mother pipe. In order to cool the processing heat, an inner surface lubricating oil and an outer surface lubricating oil are supplied.

  However, the outer surface lubricating oil used for this cooling is removed by an outer surface air blower after rolling, and the inner surface lubricating oil is scraped off by rubber or the like. In order to remove this lubricating oil, as disclosed in, for example, Japanese Patent Laid-Open No. 2000-167607 (Patent Document 1), an apparatus for removing the cold pilger mill product inner surface oil has been proposed. As a result, the inner surface lubricating oil is removed cleanly, and the amount of lubricating oil taken out of the cold pilger mill is greatly reduced.

JP 2000-167607 A

  However, as described above, local rust is generated on the inner surface of the steel pipe in the manufacturing process of the small-diameter pipe, and wrinkles due to corrosion are generated starting from the local rust. Since the cause of the inner surface rust is unknown, even if an apparatus for removing the cold pilger mill inner surface oil as described above has been proposed, the countermeasures against flaws due to corrosion have not always been perfect. Therefore, the present invention is to elucidate the generation mechanism of inner surface rust seen in small diameter pipes in these steel pipe manufacturing processes and to provide countermeasures.

In order to solve the above-mentioned problems, the inventors have intensively developed, as a result of elucidating the mechanism of local rust generation on the inner surface of the steel pipe, resulting in the invention, which is the gist of the invention Is
(1) In the method of preventing local corrosion of the steel pipe inner surface in the steel pipe manufacturing process, the steel pipe is cut to 7000 mm or less immediately after cold working, air blow is performed on the inner surface of the steel pipe, and the storage inclination angle of the steel pipe is 1 ° or more. A method for preventing local corrosion on the inner surface of a steel pipe in a steel pipe manufacturing process, wherein the process oil supplied to the inner surface of the steel pipe during cold working is degreased by performing immersion in a degreasing solution four or more times after being held in the steel.
(2) In the steel pipe inner surface local corrosion prevention method in the steel pipe manufacturing process, the air blow is performed on the inner surface of the steel pipe described in (1) within 10 minutes after cutting the steel pipe.

  As described above, according to the present invention, the processing oil on the inner surface of the steel pipe after the degreasing process can be completely removed, and as a result, the steel pipe inner surface local corrosion can be prevented.

Hereinafter, the present invention will be described in detail.
First, the local rust generation mechanism, which is the rust inside the steel pipe found in small diameter pipes in the steel pipe manufacturing process, is because the processing oil supplied to the steel pipe inside during cold working cannot be completely removed in the degreasing process. Processing oil from cold working remains on the inner surface. When this steel pipe is annealed in an annealing furnace with this processing oil remaining, when the remaining oil burns, especially in small diameter pipes, the oxygen required for complete oil combustion becomes scarce, and this is not possible. The oil is burnt and solidified and remains in a state where it adheres to the inner surface of the steel pipe.

  After that, when exposed to cooling water on the exit side of the annealing furnace, raindrops during transport in the next process, condensation, etc. in the state described above, the location where the oil is baked and solidified on the inner surface of the steel pipe is exposed to such a humid environment. Then, moisture is easily held there, and a macro corrosion battery is formed on the inner surface of the steel pipe, and as a result, local corrosion occurs on the inner surface of the steel pipe. Therefore, it was found that the phenomenon as described above does not occur if the processing oil on the inner surface of the steel pipe after the cold working is completely removed. In other words, it was found that it was necessary to remove the oil on the inner surface of the product in order not to cause local corrosion on the inner surface of the steel pipe.

  Therefore, as a means for completely removing the working oil on the inner surface of the steel pipe after the cold working, firstly, in the degreasing process after the cold working, the immersion in the degreasing liquid is performed at least four times or more. As a result, it was found that the degreasing treatment on the inner surface of the steel pipe was performed satisfactorily. However, if it is less than 4 times, the degreasing effect is insufficient. On the other hand, if it is 12 times or more, the work cost increases and the effect becomes saturated, so it is preferably 4 to 12 times.

  Secondly, in the cold working step, it is desirable to cut the steel pipe to 7000 mm or less immediately after working and to blow air from one end face of the steel pipe to the inner face within 10 minutes. However, an air blow exceeding 10 minutes is set to be within 10 minutes because the processing heat of the steel pipe is reduced, the viscosity of the processing oil is increased, and the effect of discharging the processing oil is reduced. In this way, the steel pipe immediately after processing has a high temperature due to processing heat and the viscosity of the processing oil is small, so that it is easily discharged from the inside of the steel pipe by air blow. However, when the length of the steel pipe exceeds 7000 mm, even if air blow is performed in the cold working process, the effect is not sufficient, so the length is set to 7000 mm or less.

  Thirdly, the cold-worked steel pipe is stored at an angle of at least 1 ° until it enters the degreasing process. The larger the inclination angle, the more processing oil in the steel pipe is discharged by gravity. However, if the angle is less than 1 °, the effect cannot be sufficiently achieved. Since the effect of saturation exceeding 10 ° is saturated, it is preferably 3 ° or more and 10 ° or less. However, when the length of the steel pipe exceeds 7000 mm, it is difficult to ensure a sufficient inclination angle because the steel pipe is bent by its own weight. Accordingly, the condition is that the length of the steel pipe is 7000 mm or less.

Hereinafter, the present invention will be specifically described with reference to examples.
Using a cold pilger mill to cold-roll a tubular element tube made of bearing steel to an inner diameter of 30 mm to produce a small-diameter pipe, degrease, anneal, straighten, cut, end treatment, pickling, water washing, drying Let the product get. Here, cutting after cold pilgering was performed with a tip saw. Subsequent tilting was performed by dropping the steel pipe into a tilted frame immediately after air blowing, and the steel tube was placed in a tilted storage frame after being rolled for one rod and sent to the degreasing process. The degreasing solution uses dichloromethane, and about 150 steel pipes are hung on a wire with a crane, immersed in the degreasing solution for 30 seconds, and then lifted with a crane. Degreasing 4 times means repeating this immersion and pulling up 4 times continuously.

  The steel pipe was held on the immersion tank for about 30 seconds from the time it was pulled up to the next soaking, and most of the degreasing liquid in the pipe was poured out and then immersed. The annealing conditions were 800 ° C. and 1.2 hours. For correction, rough correction was performed with a multi-roll correction machine, and then finish correction was performed with a two-roll correction machine. The cutting edge treatment was performed with a tool after emery cutting. The pickling was dipped in 13% sulfuric acid for 15 minutes, dipped in a water washing tank once, then dipped in an alkali tank once, neutralized, and naturally dried.

  In these processes, the air blowing time for the immersion treatment in the degreasing process as shown in Table 1, the cutting of the steel pipe to a certain length immediately after the cold working, and the removal of the oil adhering to the inner surface after the cutting of the steel pipe, The storage inclination angle at that time is also shown. Table 1 shows the state of adhesion of processing oil on the inner surface of the steel pipe and the results of local corrosion on the inner surface of the steel pipe when the respective conditions are changed. The adhesion of the processing oil in this case was evaluated as follows: ◎: complete removal, ◯: almost removed, △: slightly incomplete, ×: poor removal. In addition, as a result of the evaluation, the steel pipe inner surface local corrosion status was evaluated as follows: ◎: No inner surface local corrosion, ○: No inner surface local corrosion was visually observed, △: Inner surface local corrosion was observed, ×: Inner surface local corrosion occurred. evaluated.

  As shown in Table 1, no. 1 to 10 are examples of the present invention. 11-17 show a comparative example. Comparative Example No. No. 11 was incomplete in removing the deposits of processing oil because the number of immersions was small, and as a result, local corrosion on the inner surface of the steel pipe was observed. Comparative Example No. No. 12 has a long steel pipe length immediately after machining, so even if air blow was performed in the cold working process, removal of deposits on the processing oil was incomplete, and as a result, local corrosion of the steel pipe inner surface was observed. Comparative Example No. No. 13 has a small storage inclination angle, so even if air blow is performed in the cold working process, the drainage of the working oil in the steel pipe is poor, and the removal of the deposits of the working oil is incomplete. Local corrosion was observed.

  Comparative Example No. In No. 14, since the number of immersions was small and the length of the steel pipe immediately after processing was long, the removal of the deposits of the processing oil was poor, and as a result, many occurrences of local corrosion of the steel pipe inner surface were observed. Comparative Example No. No. 15 has a long steel pipe length immediately after processing and a long time until air blow after cutting the steel pipe, and therefore, the removal of the deposits of the processing oil was poor, and as a result, many occurrences of local corrosion on the inner surface of the steel pipe were observed. Comparative Example No. No. 16 has a long steel pipe length immediately after processing and no storage inclination angle. Therefore, even if air blow is performed in the cold working process, the discharge of the working oil in the steel pipe is bad and the removal of the deposits of the working oil is bad. As a result, many occurrences of local corrosion on the inner surface of the steel pipe were observed.

Comparative Example No. No. 17 has a small number of immersions and no storage inclination angle, so even if air blow is performed in the cold working process, the drainage of the working oil in the steel pipe is bad, and the removal of the deposits of the working oil is bad. Many occurrences of local corrosion on the inner surface of the steel pipe were observed.
On the other hand, No. which is an example of the present invention. It can be seen that all of 1 to 10 have good removal of deposits of the processing oil, and as a result, local corrosion on the inner surface of the steel pipe is not observed.
As described above, by completely removing the processing oil on the inner surface of the steel pipe after the degreasing process according to the present invention, as a result, when exposed to cooling water on the subsequent exit side of the annealing furnace, raindrops during transportation, condensation, etc. However, local corrosion on the inner surface of the steel pipe could be prevented.


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (2)

In the method for preventing local corrosion of the inner surface of the steel pipe in the steel pipe manufacturing process, the steel pipe is cut to 7000 mm or less immediately after cold working, air blow is performed on the inner surface of the steel pipe, and the storage inclination angle of the steel pipe is maintained at 1 ° or more. A method for preventing local corrosion of a steel pipe inner surface in a steel pipe manufacturing process, wherein the process oil supplied to the inner surface of a steel pipe is degreased by performing immersion in a post-degreasing solution four or more times. The method for preventing localized corrosion of a steel pipe inner surface in a steel pipe manufacturing process, wherein air blow is performed on the inner surface of the steel pipe according to claim 1 within 10 minutes after cutting the steel pipe.