JPS60125391A - Surface treatment of martensitic stainless steel joint for oil well pipe - Google Patents

Abstract

PURPOSE:To improve the seizing resistance of a joint for oil well pipes without deteriorating the mechanical properties of the screw parts by activating the surfaces of the threaded parts of the joint made of martensitic stainless steel having a specified Cr content by treatment in an aqueous alkali soln. and by plating the activated surfaces with Cu. CONSTITUTION:The surfaces of the screw parts of a joint for oil well pipes made of martensitic stainless steel contg. 11-14% Cr are activated by treatment in an aqueous alkali soln. having >=5% concn., and the activated surfaces are immediately plated with Cu to >=5mum thickness. Ni plating may be carried out before the Cu plating. The seizing resistance of the joint can be improved without embrittling the threaded parts.

Description

[Detailed Description of the Invention] The present invention relates to a joint made of martensitic stainless steel used for the connection part of an oil well 'a', and in particular improves the seizure resistance of the threaded part without causing embrittlement of the threaded part. The present invention relates to a surface treatment method for oil country tubular joints.

Generally, a high pressure of about 5,000 to 20,000 psi is applied to oil country tubular goods, so the joints of oil country tubular goods are required to have a high degree of airtightness. In order to ensure sufficient airtightness to withstand such high pressures, it is necessary to apply high surface pressure to the threaded portions, and as a result, the threaded portions of oil country tubular joints are susceptible to seizure and curling.

By the way, recently, the development of oil wells in harsh environments containing C02 or C02 and H2S has progressed, and the use of stainless steel as oil country tubular goods in such harsh environments has increased, especially in oil wells containing only C02. Under environmental conditions, martensitic stainless steel is more likely to attract attention.

Traditionally, in the case of oil country tubular joints made of ordinary steel or low-alloy steel, the surface of the threaded part has been coated with Sodium Sod as a preventive measure against seizure of the threaded part.
A method of plating with Zn or Zn, or a method of forming a chemical conversion coating using phosphate are employed. Among these methods, chemical conversion treatment with phosphate is inexpensive and can provide excellent anti-seizure performance in the case of ordinary steel and low alloy steel.

However, stainless steel has poor chemical reactivity compared to ordinary steel and low alloy steel, so even if it is subjected to phosphate chemical conversion treatment, the bonding strength of the formed coating to the base is low, and therefore when tightening the joint. There is a problem in that the coating peels off, and as a result, it becomes impossible to prevent the occurrence of seizure. Therefore, in the case of oil country tubular joints made of stainless steel, anti-seizure measures must be taken by plating, as described in, for example, Japanese Patent Laid-Open No. 58-31097. However, when applying anti-seizure measures using conventional plating methods to martensitic stainless steel, there are the following problems.

In other words, when plating ordinary carbon steel, hydrochloric acid or sulfuric acid is used to activate the surface.
Further, in the above-mentioned Japanese Patent Application Laid-Open No. 58-31097, when plating alloy steel containing 10% or more of Cr, i''#J1iA#J1iA is electrolytically plated in an acidic aqueous solution containing chloride. If activation treatment is performed in an acidic aqueous solution in this way, hydrogen will penetrate into the steel.In the case of ordinary steel or low-alloy steel, the penetration of hydrogen will not be so deep, but especially in martensitic stainless steel. Steel is highly susceptible to embrittlement due to the intrusion of H. Therefore, in the case of oil country tubular joints made of martensitic stainless steel, plating is performed after activation treatment in an acidic aqueous solution according to the conventional method. , the problem arises that the threaded portion becomes brittle and its mechanical properties are significantly deteriorated.

This invention was made in view of the above circumstances, and when surface treatment is applied to the threaded part of an oil country tubular joint made of martensitic stainless steel to improve seizure resistance, the deterioration of the mechanical properties of the threaded part is prevented. The object of the present invention is to provide a surface treatment method that can significantly improve seizure resistance without causing damage.

In order to achieve the above-mentioned purpose, the present inventors carried out various experiments and
As a result of repeated studies, the surface of the threaded part of an oil country tubular joint made of stainless steel was pretreated in an aqueous alkaline solution for surface activation, and then plated with one layer of Cu or two layers of Ni and Cu. It was discovered that by plating, the seizure resistance could be significantly improved without deteriorating the mechanical properties of the threaded portion, and this invention was achieved.

That is, the surface treatment method of the first invention activates the surface of the threaded portion of an oil country pipe joint made of martensitic stainless steel containing 11 to 14% Cr by weight in an alkaline aqueous solution of 5 or more. It is characterized in that Cu plating with a thickness of 5 μm or more is applied immediately after the treatment.

In addition, in the surface treatment method of the second invention, after the surface of the threaded portion of the oil well pipe joint similar to the above is activated in an alkaline water bath solution with a concentration of 5% or more, KNi plating is immediately applied, and the thickness is further increased. It is characterized by applying Cu plating with a thickness of 5 μm or more.

The surface treatment method of the present invention will be explained in detail below.

The oil well pipe joint to which this invention is directed is made of martensitic stainless steel containing 11 to 14 Cr. If Cr is less than 11, it is difficult to cause seizure, so there is no need to apply this invention.On the other hand, if Cr exceeds 14, activation in an alkaline aqueous solution becomes difficult, so Cr of the target material is 11-14
%.

The threads of such oil country tubular joints made of martensitic stainless steel are first activated using an alkaline aqueous solution, and then immediately coated with Cu plating or two-layer plating of Ni plating and Cu plating. By this,
A plated layer that is free from hydrogen embrittlement and has high bonding strength can be obtained. That is, since the method of the present invention performs the activation treatment using an alkaline aqueous solution instead of the acidic water bath solution conventionally used for the activation treatment, hydrogen is not absorbed into the base material made of martensitic stainless steel during the activation treatment. There is no penetration, therefore no embrittlement due to hydrogen occurs, and the activation treatment also increases the bonding strength of the plated layer. However, if the concentration of the alkaline aqueous solution used in the activation treatment is less than 5%, the activation of the martensitic stainless steel surface will be insufficient, the degree of bonding of the plated layer will be low, and as a result, the excellent seizure resistance will be reduced. I can't get it. Therefore, it is necessary to use an alkaline water bath solution with a concentration of 5% or more.

The alkaline aqueous solution is typically a NaOH aqueous solution, but it is also possible to use KOH or the like.

Further, in the method of the present invention, Cu plating is applied after activation with an alkaline aqueous solution, or Cu plating is applied after Ni plating, and the reason for selecting such a plating metal is as follows. In other words, Cu plating has superior seizure resistance compared to the conventionally used Zn plating and Sn plating, and in particular, if Ni plating is applied and then Cu plating is applied on top of that, the seizure resistance is further improved. . However, if the thickness of the Cu plating layer is less than 5 μm, the anti-seizure effect of the Co plating layer will not be sufficient, so the thickness of the Cu plating layer must be 5 μm or more. Further, in the case of two-layer plating of Ni + Cu, the thickness of the Ni plating layer is not particularly limited, but it is usually preferably about 1 to 20 μm.

Examples of the present invention will be described below along with comparative examples.

Steel pipes are manufactured using martensitic steel with the three types of compositions shown in Table 1, and are further threaded to form the oil country tubular goods 1 shown in Figure 1.
And a coupling joint 2 was obtained.

In addition, here the joint is ``API 5pec 5AX: )
Iigh-8 strengthCasing, Tubi
"External-upset" specified in Table 6.5 of ng and DrIll Pipe'
The outer diameter of the part of the oil country tubular body is 35" and the plate thickness is 0.
．． 254", the outside diameter of the upset part is 3.75", and the outside diameter of the coupling joint 2 is 4.5", and the length is 537".
It is 4″.

The threaded portion of such a coupling joint 2 was plated by the method shown below. That is, first degrease by boiling at 90°C for 15 minutes with a commercially available alkaline degreasing solution, wash with water, and then
80°C in a solution in which 5 g of a chelating agent was added to an aqueous solution of O and NaOH, and in some cases, 5 g of H2O2 was added.
Activation treatment was carried out for 10 minutes as a comparative example.
H2804 water bath solution at 60℃XtO for minutes or l
Activation treatment was performed for 50"CX10 minutes in an O% MCI aqueous solution. Immediately thereafter, Cu plating, Ni+Cu two-layer plating, Zn plating, or Sn plating was performed. Here, Cu plating was performed by electroplating, and the bath composition was are CuCN 40t/II, NaCN 8Wll
, temperature is 70°C, current density is 1-2.5 A/d
m2. In addition, in the case of two-layer plating, Ni plating on the F base is performed by immersion plating, and the bath composition is Ni 9 Wll.
1, hypophosphite 28 Wll1.

The temperature was 90°C. On the other hand, Zn plating is performed by electroplating, and the bath composition is Zn l 79y'il, C6
180f! 7/l, temperature is 2o'c, current density is 2
A/dm.

In addition, Sn plating is performed by electroplating, and the bath composition is 5
nSO440Wll, H2So460 ElA, cresol sulfonic acid 40'if/l, bath temperature 2
The temperature was 0°C and the current density was 2A7dm2.

The coupling joint 2 and the oil country tubular goods 1 each have a plating layer formed on their threaded portions as described above. Next, the coupling joint was removed and the surface of the threaded part was visually inspected to check for the occurrence of seizure. (The roughness of the surface of the stainless steel is 0.05W or less).On the other hand, if seizure occurs, the plating on the burned part will peel off and the surface of the stainless steel will be exposed, and the surface roughness will be 0.
111111 or higher, and therefore it was possible to clearly distinguish whether or not burn-in occurred. In addition, for coupling joints that have not been heat treated (that is, those that have not been subjected to activation treatment and plating treatment) and coupling joints that have been plated, 2111 + V
Collect a Nocchi Charbee impact test piece (full size),
A Charpy impact test was conducted to measure the absorbed energy value at 0°C. The degree of embrittlement was determined based on the difference between the energy absorbed in the joint as heat treated and the energy absorbed in the joint after plating.

The results of these tests are shown in Table 2. In addition, in the second front opening, examples 1 to 5 of the present invention and comparative examples 6 to li? 'iAll of these tests were carried out on the three steel buildings shown in Table 1.
The difference between steel and German steel was not significant.

Table 2 * Degree of embrittlement = (Charpy absorbed energy of material as heat treated (at 0°C)) - (Charpy absorbed energy of material after plating (at 0°C)) As is clear from Table 2, alkaline aqueous solution Cu plating with a film thickness of 5 μm or more after activation with Ni, or CU with a film thickness of 5 μm or more after Ni base plating
It was confirmed that in Examples 1 to 5 of the present invention ψ, which were plated, there was very little embrittlement of the threaded portion of the plated screws, and there was no occurrence of warp or burnout, showing excellent resistance to burn marks. On the other hand, in Comparative Example 6, the surface was activated with sulfuric acid, so it became brittle due to hydrogen. However, because Cu plating was applied,
No burn-in occurred. Further, in Comparative Example 7, the surface was activated with hydrochloric acid, so it became brittle due to hydrogen, but since Cu plating was applied, no seizure occurred. In Comparative Example 8, embrittlement due to hydrogen occurred because the surface was activated with sulfuric acid, but no seizure occurred because Cu plating was applied after Ni plating. In Comparative Example 9, embrittlement due to hydrogen did not occur because the surface was activated with an alkaline aqueous solution, but seizure occurred because Zn plating was applied. Comparative Example 1O was also activated at night with alkaline aqueous C, so no embrittlement due to hydrogen occurred; Horsetail 1〆2-″l・Black-・--Shi5do41zu11ku++L-
Since the surface was activated by alkaline water, embrittlement due to hydrogen did not occur, but seizure occurred because the thickness of the Cu plating was as small as 2 μm.

As is clear from the above description, according to the surface treatment method for oil country tubular joints of the present invention, the threaded portions of oil country tubular joints using martensitic stainless steel as the base material do not become brittle.
It is now possible to rely on Yui WGI, which has excellent seizure resistance.

[Brief explanation of the drawing]

FIG. 1 is a schematic exploded sectional view showing the state when the oil well 'R vertical joint is connected in an embodiment of the present invention. l...oil country pipe, 2...coupling joint, 3...
screw part. Applicant: Kawasaki Steel Co., Ltd. Agent: Taketo Toyota, patent attorney (and one other person)

Claims (1)

[Claims] (1) After activating the threaded surface of an oil country tubular joint made of martensitic stainless steel containing 11 to 14% Cr by weight in an alkaline aqueous solution with a concentration of 5% or more, + A method for surface treatment of oil country tubular joints made of martensitic stainless steel, characterized by applying Cu plating with a thickness of 5 μm or more. (After activating the surface of the threaded part of the oil well I# vertical joint, which is made of martensitic stainless steel containing 2J Cr in an Mt ratio of 11 to 14 cm, in an alkaline aqueous solution with a concentration of 5 cm or more, 1a immediately Ni-plated and further thickened to 5μ
A method for surface treatment of martensitic stainless steel JN oil country pipe fittings, characterized by applying Cu plating of m or more.