JPS59177383A - Structure for preventing stress corrosion cracking of stainless steel - Google Patents

Abstract

PURPOSE:To prevent the stress corrosion cracking of a stainless steel member by plating the surface of the member contacting with a corrosive medium with a platinum group metal. CONSTITUTION:A member for an apparatus for the chemical industry is made of stainless steel, and the surface of the member contacting with a corrosive medium such as chlorine ions or bromine ions is plated with a platinum group metal having small ionization tendency, preferably rhodium. The stress corrosion cracking of the stainless steel member can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the prevention of stress corrosion cracking in stainless steel.

(Prior art) Stainless steel has excellent high-temperature strength, workability, weldability, and corrosion resistance, so it is widely used in chemical industry equipment such as acetic acid manufacturing plants and petrochemical plants. Due to the I%A effect of corrosion, cracking occurs even when the working stress is sufficiently high (hereinafter, this cracking is referred to as stress corrosion cracking).
These cracks caused problems such as failure of each glazing device and leakage of dangerous liquids.

As shown in Fig. 1, stress corrosion cracking of stainless steel is caused by, for example, welding, at the interface with a solvent containing halogen ions (particularly chlorine ions or bromine ions). When tensile stress exists as residual stress inside, local corrosion occurs due to halogen ions such as chlorine ions, and this corrosion occurs because the corroded parts are expanded by the action of the tensile stress. In addition,
Reference numeral 4 is a welded portion.

Stress corrosion cracking of stainless steel occurs when the load stress is only 2~
3P, 9/m2, it cracks within 2 to 3 months to 1 year after the start of practical use, and may crack after several years to 10 years, so it is difficult to predict the occurrence of stress corrosion cracking, and It is also virtually difficult to reduce the stress generated within each member of the device.

Therefore, we decided to use stainless steel as a cand.1. There is a cand corrosion protection method in which a separately provided insoluble electrode is used as an anode in direct contact with a DC power source, and the stainless steel is cathodically polarized to its corrosion protection potential range to prevent corrosion.However, it cannot be used in all locations and is expensive. Therefore, there has been a need for a means to reliably prevent stress corrosion cracking that is convenient and low cost.

As a result of experiments, the inventors have confirmed that local corrosion can be avoided by applying platinum group plating to stainless steel, which is susceptible to attack by chlorine ions or bromide ions, and have achieved the present invention.

(1:1 aspect of the invention) The present invention was made in view of the above-mentioned drawbacks of the prior art, and its purpose is to prevent stress corrosion cracking by cutting off contact with a corrosive medium of a frame made of stainless steel. There is a particular thing.

(Structure of the Invention) The present invention applies a plating treatment to the interface with corrosive media such as chlorine ions or bromide ions of a frame made of stainless steel used in various devices for chemical T millet. It is a stainless steel structure that prevents stress corrosion cracking. This configuration achieves the above objective.

Figure 2 is a cross-sectional view of a stainless steel plate 2 that has been subjected to rhodium plating 6. Chlorine ions, which cause local corrosion on stainless steel, come into contact with the rhodium layer, but rhodium has a small ionization tendency and is not corroded. The surface is not exposed to chlorine or ions.

A stainless steel plate (SUS304) having a welded part is plated with ruthenium, platinum, rhodium 16, and palladium to a thickness of 3 to 6 μm each, and is then plated with dissolved oxygen of approximately 8 p, p, m using an autoclave. Tables 1 and 2 show the results of a stress corrosion cracking experiment conducted by immersing the sample in water containing 50p, p, m2 of Br- at a temperature of 250°C for 240 hours.

(Table 1) (Table 2) The thickness is 6 μIn) Table 1 shows the results of the first experiment, and Table 2 shows the results of the second experiment. Even with ruthenium plating and varnish plating treatments, stress corrosion cracking occurred, similar to stainless steel sheets with no surface plating treatment. therefore,
Ruthenium plating and palladium plating have no effect on preventing stress snacking cracking.

In the case of platinum plating, the length in the first experiment was perpendicular to the plating surface],
A small number of extremely small stress corrosion cracks of Q 3 mm occurred. However, in the second experiment, stress corrosion cracking did not occur at all in both cases of thin plating with a plating thickness of 3 μm and thick plating with a plating thickness of 6 μm.

When rhodium plating is applied, the first and second
Stress corrosion cracking did not occur at all in either case of thinning or thickening.

(Example) In Figures 3 and 4, the present invention is applied to a flange portion of a chemical plant piping made of stainless steel.

The matching surfaces of the flange portions 12A and i3A of the tube body 12, ]3 are plated with rhodium 14 having a thickness of 4 μm.

Reference numeral 16 is a casket for preventing the internal solution from leaking, reference numeral 18 is a bolt/nut for tightening the tubes 12 and 13, and reference numeral 20 is a bolt insertion hole.

Since the flange parts 12A and 13A are in contact with the outer periphery of the end of the six pipes 12.13, the flange parts 12A and 13A are easily susceptible to stress corrosion; Wow, the transformation of tube body 12.13! ! 8. In the county, the flow tends to stagnate, and the concentration of chlorine ions can be falsified, making it easy for eclipses to occur.

Since the matching surfaces of the flange parts 12Δ and 13A are completely rhodium plated, the inner surfaces of the flange parts 12A and 13A are completely cut off from contact with chlorine ions, so that the matching surfaces of the flange parts 12A and 13A are locally coated. Partial corrosion does not occur and stress corrosion cracking is prevented. Furthermore, crevice corrosion is also suppressed.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, since platinum group plating is applied to the silver surface of stainless steel, stainless steel is not exposed to corrosive media and stress corrosion can occur. Local corrosion, which is one of the necessary elements, does not occur,
the! 1.Near flattened tail and force corrosion cracking are prevented.

Although the present invention can be applied to places 79i where the flow of the corrosive medium is fast, it is recommended to apply it to places where the flow is relatively slow and fast since the plating layer is likely to be peeled off due to flow friction. J lever is also desirable.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a stainless steel plate with stress corrosion cracking, Fig. 2 is a cross-sectional view of a stainless steel plate with rhodium plating, and Fig. 3 is a cross-sectional view of a stainless steel plate with stress corrosion cracking. The cutaway view and FIG. 4 are perspective views thereof. 2... Stainless steel plate, 4... Welded part, 6... Rhodium plating layer.

Claims (2)

[Claims] (1) A structure for preventing stress corrosion cracking of stainless steel, characterized in that a platinum group plating treatment is applied to the interface between the frame made of stainless steel and the corrosive medium. (2) A structure for preventing stress corrosion cracking of stainless steel according to item 1 of the scope of Patent No. 874, wherein the platinum group metal is rhodium.