GB2149321A - Coated steel - Google Patents

Abstract

A hydrogen absorption-controlling coated steel article has a metal layer from 0.05 to 1 mu m thick between the steel surface and a coating or lining.

Description

SPECIFICATION Coated steel The present invention relates to steel having a coating for preventing hydrogen embrittlement, i.e. the cracking arising from hydrogen absorption.

Steel articles exhibit stress corrosion cracking in the presence of hydrogen sulfide or carbonic acid gas. It is believed that atomic hydrogen formed by reaction of hydrogen sulfide with the steel are absorbed, and diffuse, into the steel, and cause hydrogen embrittlement.

In order to prevent hydrogen embrittlement, a coating or lining has been used to isolate corrosive reagents such as hydrogen sulfide from the steel. It has been proposed to add to a coating composition an ion-exchange resin or a metallic powder (pigment) reactive with hydrogen sulfide. The additives' reactivity prevents hydrogen sulfide passing to the surface of the steel, but the reaction cannot continue indefinitely. The initial effect of the additive decreases rapidly, and the corrosion reaction increases, in use. In the given cases, the corrosion reaction generally begins to increase, often after 30 hours and usually within 100 days, from application of the coating composition. Such a period is very short in comparison with the actual use term of the steel (50-60 years).

According to the present invention, a steel article has a coating or lining and, in between, a metal layer from 0.05 to 1 ssbm thick.

The metal layer used in the pesent invention can be formed on the steel surface by electroplating, electroless plating, composite plating of a mixture of a metal with an organic material such as a polymer resin, melt plating or sputtering. Examples of suitable metals are aluminum, nickel, chromium, cadmium, copper, lead and the like. These metals can react with hydrogen sulfate and carbonic acid gas to form an inert film. Preferred merals are nickel, chromium, cadmium, and copper.

Thickness of the metal layer is from 0.05 to 1 ym, preferably from 0.08 to 0.5 ,um. Less than 0.05 lim is not desirable because a technical effect for controlling the hydrogen absorption by the corrosion becomes small. Above 1 ,um, the technical effect for controlling the hydrogen absorption can become high, however it becomes difficult that hydrogen absorbed into the steel is emitted to outside the steel.

According to the present invention, a coating or lining is applied to the metal layer in order to prevent hydrogen sulfate and carbonic acid gas from transmitting to the steel. Examples of these coating and lining can be those which can be used for an anticorrosion paint. Examples of the resin used in the anticorrosion paint a polymerized oil, a natural and synthetic resin.

Typical example of the polymerized oil is a boiled oil. Examples of the natural or synthetic resin are an epoxy resin, an epoxy-urethan resin, an epoxy coal tar resin, a melamine resin, a rubber chloride, a phenol resin, a polyester resin, a polyurethan resin, a silicone resin, a fluororesin, and the like.

A process for coating can be any conventional process such as flow, dipping, spray, brush, or powder coating.

The steel to be employed is one which can form or forms easily the stress corrosion, the hydrogen embrittlement, the hydrogen induced cracking, the hydrogen blister and the like.

Typical examples of the steel are a carbon steel, an alloy, a high tensiled steel and the like which are used for an oil field pipe, a transfer line pipe, a bolt, an assembly of a ship and the like.

The coated steel of the present invention hardly absorbs the atomic state hydrogen formed by the corrosion of the steel under the atmosphere containing hydrogen sulfate. Accordingly, the metal layer of the present invention controls effectively the hydrogen embrittlement. It is believed that the reason why the metal layer of the present invention prevents the hydrogen embrittlement is that the corrosion potential of the surface of the steel is kept noble by the metal layer or a reaction product layer of the metal layer of the present invention (an absorption of the atomic state hydrogen would be accelerated if the corrosion potential of the steel surface is a less-noble potential).

The present invention is illustrated by the following examples, which, however, are not to be construed as limiting the invention to their details. All parts and percentages in the examples are by weight unless otherwise specified.

Example 1 A metal layer and a coating was formed on the a cold rolled steel (thickness 0.8mm, JIS G 3141) by the method as shown in Table-1. In stead of the cold rolled steel, an use of a high tensiled steel is naturally required for an evaluation of the hydrogen embrittlement crack, but since the technical effect of the present invention can be evaluated by whether the hydrogen absorption reaction is good or not, the cold rolled steel was used in the present example. The method of coating was a spray coating.

For the purpose of comparison, a metal layer of 0.02 ym and 10 pm formed on the above steel by the method as shown in Table.

In order to evaluate the controlling property of hydrogen absorption, a change on standing of the current based on the reaction H H + + e - which is an extract reaction of hydrogen on the hidden side of the steel was measured. The measurement is based on the method described in Japanese Patent No. 1018241, the portion of which are hereby incorporated by reference.

The method of the evaluation is illustrated with referring to Fig. 1. The curve X of Fig. 1 shows a change on standing of a reaction current for an extract of hydrogen with the coated steel not containing the metal layer of the present invention, and the curve Y of Fig. 1 shows a change on standing of a reaction current for an extract of hydrogen using the coated steel having the metal layer. Increase of the current shows that the hydrogen disolved in the steel by the corrosion reaction of the steel surface under the coating is extracted from the opposite side of the steel. Accordingly, the latter build up shows the better corrosion control. The evaluation of the present invention shows as ty/tx which indicates a rate of build up times of the both. The result and the condition of the corrosion is shown in Table 1.

Table 1

Example thickness thickness ty/tx number metal of plate name of the paint drying condition of film ratio corrosion condition ( m) ( m) Hydrogen sulfide and carbonic 1 Ni 1 SUPERLAC DIF, F-80, N-23 190 C/10sec. 20 23 acid was continuously blowed to (plating) (epoxy polyurethan paint) 3% NaCl solution. Temp. 50 C Hydrogen sulfide and carbonic 2 Ni 1 COPON MASTIC PRIMER natural drying 60 12 acid was continuously blowed to (plating) (epoxy resin paint) 10days 3% NaCl solution. Temp. 70 C EPOTAR S Hydrogen sulfide and carbonic 3 Ni 1 (JIS K-566) natural drying 70 31 acid was continuously blowed to (plating) (epoxy coal ter pait) 10days 3% NaCl solution. Temp. 50 C Hydrogen sulfide and carbonic 4 Ni 1 Hi-RUBBER E PRIMER natural drying 40 25 acid was continuously blowed to (plating) (rubber chloride paint) 10days 3% NaCl solution. Temp. 30 C Hydrogen sulfide gas of 100% 5 Ni 1 SULPHOTITE 10 natural drying 25 46 relative humidity.

(plating) (phenol resin paint) 10days Temp. 70 C Hydrogen sulfide gas of 100% 6 Ni 1 SUNFTAL 20 natural drying 25 14 relative humidity.

(plating) (phthalic acid paint) 10days Temp. 70 C Hydrogen sulfide gas of 100% 7 Ni 1 ORGA 100-2 natural drying 20 36 relative humidity.

(plating) (melamine resin paint) 10days Temp. 30 C Hydrogen sulfide and carbonic 8 Ni 1 CYANAMID HELGON QO PRIMER natural drying 35 9 acid was continuously blowed to (plating) (JIS K-5625-2) 10days 3% NaCl solution. Temp. 30 C Hydrogen sulfide was conti9 Ni 1 INTERGARD GLASS FLAKE natural drying 2000 28 ously blowed to 3% NaCl (plating) (epoxy resin paint) 10days solution. Temp. 60 C NIPPE ZINKY 1000P Hydrogen sulfide was conti10 Ni 1 (zinc powder containing natural drying 20 24 ously blowed to 3% NaCl (plating) paint) 10days solution. Temp. 20 C Table 1 (continued)

Example thickness thickness ty/tx number metal of plate name of the paint drying condition of film ratio corrosion condition ( m) ( m) Hi-CR PRIMER WHITE Hydrogen sulfide was continu11 Ni 1 (JIS K-5506) natural drying 2016 ously blowed to3% NaCl (plating) (synthetic resin paint) 10days solution. Temp.50 C Hydrogen sulfide and carbonic 12 Ni 1 POWDAX P natural drying 50 11 acid was continuously blowed to (plating) (powder coating) 10days 3% NaCl solution. Temp.70 C Hydrogen sulfide was continu13 Al 0.5 ORGA 100-2 natural drying 10 23 ously blowed to 3% NaCl (sputtering) (melamine resin paint) 10days solution. Temp.40 C Hydrogen sulfide was continu14 Cr 1 ORGA-2 natural drying 10 47 ously blowed to 3% NaCl (plating) (melamine resin paint) 10days solution. Temp. 40 C Hydrogen sulfide was continu15 Cd 0.5 ORGA 100-2 natural drying 10 32 ously blowed to 3% NaCl (plating) (melamine resin paint) 10days solution. Temp.40 C Ni Hydrogen sulfide gas of 100% 16 (vapor phase 0.5 POWDAX P natural drying 30 13 relative humidity.

plating) (powder coating) 10days Temp.70 C Hydrogen sulfide gas of 100% 17 Cu 0.8 EPOTAR S (JIS K-560) natural drying 40 19 relative humidity.

(plating) (epoxy coal tar paint) 10days Temp.70 C Ni Hydrogen sulfide gas of 100% 18 (plating WEISBERG 1 EPOTAR S (JIS K-560) natural drying 40 29 relative humidity.

BATH) (epoxy coal tar paint) 10days Temp.70 C Ni Hydrogen sulfide + carbonic acid 19 (plating saccharin 1 EPOTAR 5 (JIS K-560) natural drying 40 26 was continuously blowed to containing grose bath) (epoxy coal tar paint) 10days ion-exchange water. Temp.60 C Hydrogen sulfide + carbonic acid 20 Ni 1 EPOTAR S (JIS K-560) natural drying 40 38 was continuously blowed to (plating WATT BATH) (epoxy coal tar paint) 10days ion-xchange water. Temp.60 C Table 1 (continued)

Example thickness thickness ty/tx number metal of plate name of the paint drying condition of film ratio corrosion condition ( m) ( m) Comparative Hydrogen sulfide + carbonic acid Example Ni 0.02 SUPERLAC DIF, F-80, N-23 natural drying 20 3 was continuously blowed to 1 (electrolytic plating) (epoxy polyurethan paint) 10days ion-exchange water. Temp.50 C Example Hydrogen sulfide + carbonic acid 21 Ni 0,05 SUPERLAC DIF, F-80, N-23 natural dryin 20 18 was continously blowed to (electrolytic plating) (epoxy polyurethan paint) 10days ion-excahange water. Temp.50 C Hydrogen sulfide + carbonic acid 22 Ni 0.1 SUPERLAC DIF, F-80, N-23 natural drying 20 20 was continously blowed to (electorlytic plating) (epoxy polyurethan paint) 10days ion-exchange water. Temp.50 C Hydrogen sulfide + carbonic acid 23 Ni 1 SUPERLA DIF, F-80, N-23 natural drying 20 23 was continously blowed to (electrolytic plating) (epoxy polyurethan paint) 10days ion-exchange water. Temp.50 C Comparative Hydrogen sulfide + carbonic acid Example Ni 10 SUPERLAC DIF, F-80, N-23 natural drying 20 81 was continuously blowed to 2 (electrolytic plating) (epoxy polyurethan paint) 10days ion-exchange water. Temp.50 C Since this measurement is conducted by an electrochemical method, it is 100 times sensitive rather than a conventional gas measurement. Accordingly, measuring time of ty is stopped up to 1,000 hours, ty is regarded as 1,000 unless the ty point is observed. It is possible that the coating layer is thick enough to reduce the value of ty/tx as the result of the big value of tx, in spite of the exsistence of the metal layer of the present invention, (for example, the coated steel with super-high thickness of coating layer in order to improve the interruption-effect as lining).

The value of ty/tx, however, is not less than 4 or so, in the examples of the present invention, so that the metal layer in this invention is enough to be effective.

Example II This example indicates that the metal layer of the present invention holds the potential of the steel surface noble by measuring a corrosion potential on the side of the coating.

The paint containing 100 parts by weight of melamine alkyd resin, 10 parts of titanium oxide(X-1) and 10 parts of iron oxide red(X-2) was applied to the cold rolled steel as described in Example I to compare with the coated steel of the present invention having the metal layer. A saturated solution of 3% NaCI + H2S(gas) was contacted with the coating. A silver-silver chloride electrode was put into the saturated solution with a salt bridge. The potential difference between this salt bridge electrode and the steel was measured. The result is shown on Fig. 2.

As indicated in Fig. 2, when the steel did not have the metal layer or when the paint contained the substance which can react with hydrogen sulfide, the corrosion potential of the steel was not kept noble and changed to less-noble on standing. On the other hand, in the present invention, the corrosion potential was held noble to control hydrogen absorption by an electrochemical reaction.

Example 111 In this example, a degree which hydrogen disolved in the steel is emitted is measured.

Determination was carried out by using an apparatus of Fig. 3. A container (3) and a container (4) was installed on the both sides of a steel (1) with using a fastening (not shown) through a packing (2). The container (3) was filled up with a corrosive liquid such as water and the like. Inside of the container (4) was made a vacuous to from 10-2 to 10-7 Torr by a vacuum pump which was connected by opening a valve (6) through a pipe (5) and then the valve (6) was closed. A constant electric current (1 mA) was sent between the steel (1) and a platinum counter electrode so that hydrogen was absorbed into the steel (1) at a constant rate through the surface in corrosive side of the steel (1). The hydrogen in the steel is evolved into the vacuum inside of the container (4) through the surface that is the opposite side of corrosive side by means of the above-mentioned operation. The hydrogen is introduced into mass-spectro meter (9) through the pipe (5). The peak height of mass-spectrum with 1 or 2 in mass number (m/z) is indicated in voltage. The peak height in case that mass number is 2, is shown in table 3 in examples 21 to 23 and comparative examples 1 and 2.

Table 3 Example Peak height of mass (comparative example) spectrum (mV) 1 840 21 4900 22 5100 23 4800 2 290 The coated steel without the metal layer indicated 250 mV in peak height of mass spectrum.

Accordingly, coated steels of comparative examples showed that the emission property was very low.

Claims (6)

1. A steel article having a coating or lining and, in between, a metal layer from 0.05 to 1 ,xm thick.

2. A steel article according to claim 1, in which the metal of the layer is aluminium, nickel, chromium, cadmium or copper.

3. A method for producing a coated steel article, which comprises (a) forming a metal layer from 0.05 to 1 ,um thick on a surface of a steel article, and (b) applying a coating or lining to the metal layer.

4. A method according to claim 3, in which the metal of the layer is aluminium, nickel, chromium, cadmium or copper.

5. A method according to claim 3 or claim 4, in which the metal layer is formed by sputtering.

6. A method according to claim 3, substantially as described in any of the Examples.