JPS6250488A - Descaling method for steel products - Google Patents

Abstract

PURPOSE:To thoroughly remove the scale of a structure consisting of a high- chromium steel and material essentially composed of high chromium at a low temp. in a short period by immersing the above-mentioned structure into an acid soln. contg. a phosphoric acid as an essential component and subjecting the structure to an ultrasonic wave treatment. CONSTITUTION:Intricately shaped parts 5 such as water feed header which are manufactured of the high-chromium steel products and are subjected to annealing and heat treatment after working such as bending and welding are immersed into the acid soln. 4 contg. the phosphoric acid as the essential component in a cleaning vessel 1. The ultrasonic waves of prescribed oscillation frequencies are then generated from respective oscillators 2 in the soln. 4 by an ultrasonic wave generator. The dense scale of a high chromium content on the parts 5 is thus easily and efficiency stripped away by the corrosion of the soln. 4 and the impact of the ultrasonic waves without damaging the base material and decreasing the weight thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for removing scale from high chromium steel.

[Prior Art] For example, heat exchanger tube headers and the like of heat exchangers are increasingly manufactured using high chromium steel such as 9% chromium steel.

Various parts manufactured using the high chromium steel are subjected to heat treatment such as annealing after bending, welding, etc., so scales such as iron oxide are formed on the surface.

In order to remove this scale, the parts are immersed in a suppressive phosphoric acid solution, which is a conventional descaling method for steel materials, and the r! A method is used in which the Ii solution is circulated and heated (approximately 60° C.) for several hours (approximately 6 hours).

[Problems to be solved by the invention] However, since the base material of the scale is high chromium steel,
Its composition is a composite oxide of iron, chromium, and oxygen, with a high content of chromium, and is much denser than the general magnetite scale, so conventional pickling has almost no descaling effect. There are problems such as poor paintability, and residual swamp scale that easily peels off during the oxidation process of the base material.

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, in the present invention, a structure made of high chromium steel and a material mainly composed of high chromium is replaced with a structure made of high chromium steel and a material mainly composed of high chromium. The sample was immersed in an acid solution and subjected to ultrasonication.

1 Effect] The scale of high chromium steel parts becomes brittle due to the impact of ultrasonic waves, making it easy for the acid solution to penetrate into it, and when it is eroded by the acid solution and becomes easy to peel off, the scale is exposed to the impact of the ultrasonic waves. It can be easily removed without damaging or reducing the base material.

[Implementation Example 1] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the implementation state of the present invention, in which the inner surface of a cleaning tank 1 is coated with stainless steel (for example, 5O3304, etc.), and a required number of ultrasonic movers 2 are arranged at required positions in the cleaning tank 1. Then, each ultrasonic transducer 2 is connected to an ultrasonic generator 3. An acid solution 4 containing phosphoric acid as a main component is placed in the cleaning tank 1, and parts 5 such as water supply headers made of high chromium steel, annealed and heat treated after bending, welding, etc. are placed in the acid solution 4. The ultrasonic generator 3 generates a predetermined number of ultrasonic waves from each pregnant child 2 to remove scale on the surface of the component 5.

Here, if necessary, a heating heater may be buried in the cleaning tank 1, and the heating heater may be used to clean the cleaning (acid) mixture 4 at 20 to 60°C. The temperature may be raised within the range of .

The composition of Butyrus'fi4 is 5-25% phosphoric acid, 0.01-
The cleaning effect is further enhanced by using 1% of an amine corrosive agent (IBIT #530) and adding a surfactant such as 0.01 to 1% of a nonionic surfactant (Ribonoxt 1). As the surfactant, in addition to nonionic surfactants, a wide variety of surfactants such as cationic surfactants, anionic surfactants, etc. can be used.

As for the frequency of the ultrasonic waves, H2 is suitable between 10 and 500, and preferably about 36 TLZ.

Although the treatment time varies depending on the treatment temperature, 3 to 6 hours is appropriate for heating treatment, and 6 to 10 hours is appropriate for room temperature treatment.

Example 1 A 9 chromium steel annealed test piece with a scale was treated with 21% phosphorus 1-o.
, i% corrosion inhibitor acid solution and 21% phosphorus 11-0.1
% [Using an acid solution of regular eating suppressant - 0.1% surfactant, ultrasonic wave <36 kHz shown in Table 1 below] Presence of quick burial, processing temperature ('C), processing time (III'), etc. The test piece was descaled under the following conditions and reduced in scale (mg,/cm
), dissolved ions (iron [e, chromium Cr, mg/c
m'), 33 minute (suspended solid content) incidence, descaling status, and corrosion rate (mM cm'-Hr).

The results are shown in Table 1.

By ultrasonication, scale could be completely removed at a lower temperature and in a short time, whereas in the case of no ultrasonication, most of the scale remained. Since the dissolved ions of iron and the corrosion rate are significantly reduced, there is very little wear and tear on the base metal, and the scale removal effect is also high, making it ideal.

In the case of normal temperature treatment, a relatively long time is required, but since the treatment conditions are mild, there is little wear on the base material.

However, the incidence rate of SS is extremely high.

Example 2 By adding a surfactant, the descaling effect is further promoted, so that the processing time can be further shortened. Example 2 MCI (-9) 1 annealed and scaled test piece was prepared from Example 1. Using the same acid solution as above, descaling was carried out under the conditions shown in Table 2 below, and the same test as in Example 1 was conducted. The results are shown in Table 2 below.

In this example, almost the same tendency as in Example 1 was observed, and excellent ultrasonic treatment effects and surfactant addition effects were obtained.

It should be noted that the method for removing scale from steel materials according to the present invention is not limited to the above-described embodiments, and it is of course possible to make various changes without departing from the gist of the present invention.

[Effect 1 of the Invention As explained above, the method for removing scale from steel materials of the present invention exhibits various crushing effects as described below.

(D) Since ultrasonic waves are used in conjunction with acid cleaning, scale that can hardly be removed by pickling can be completely and easily removed by ultrasonic waves.

Therefore, paintability etc. are improved.

<n> Since ultrasonic waves are used in combination, the processing temperature can be low and the processing time can be significantly shortened.

([ID Because the processing conditions are relaxed, wear and tear on the base material is significantly reduced.

(2) When surfactant 8 is added to the acid solution, the acid solution blends well with the surface of the school, promoting the descaling effect and further enhancing the effect of <I[8].

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the implementation state of the method of the present invention. 1 is a cleaning tank, 2 is an ultrasonic wave generator, 3 is an ultrasonic generator, 4 is an acid solution, and 5 is a component.

Claims (1)

[Claims] 1) A method for removing scale from steel materials, which comprises immersing a structure made of high chromium steel or a material mainly consisting of high chromium in an acid solution containing phosphoric acid as a main component, and subjecting it to ultrasonic treatment.