JPS6179797A - Oil well pipe joint having excellent resistance to galling and corrosion - Google Patents

Abstract

PURPOSE:To provide a titled high chromium content oil well pipe joint which is made low in cost by constituting said joint of screw parts which are plated on the surface with Zn, Sn, Pb, the alloy thereof, etc. and metal sealing parts which are plated on the surface with gold, platinum group metal, the alloy thereof, etc. CONSTITUTION:This oil well pipe joint is constituted of the box of a coupling pipe 2 and the pin of an oil well pipe 1 and is provided with the metal sealing parts 4, 4' and screw parts 3, 3' consisting of the high chromium content steel contg. >=10% Cr. The surfaces of the screw parts 3, 3' of such joint are plated with 1 kind among Zn, Sn, Pb, Cu and the alloy thereof having galling resistance and the surfaces of the metal sealing parts 4, 4' consisting of the above- mentioned main sealing parts 5, 5' and sub-sealing parts 6, 6' are plated by 1 kind among gold, platinum group metal and the alloy thereof having excellent corrosion resistance. The above-mentioned plating layers are preferably formed to about 0.1-20mum thickness. The noble metal plating layers may be thin but the parts 3m 3' are preferably thickly plated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides an oil country tubular joint made of high chromium-containing steel, particularly comprising a threaded portion and a metal seal portion, each of which is plated with a different type. , relating to an oil country tubular joint with excellent galling resistance and corrosion resistance.

(Prior art) Stone 7Tl] With the progress of resource development, oil wells have become deeper in recent years, forcing crude oil extraction under high temperature, high pressure, and even highly corrosive environments. Under such conditions, pipe joints with extremely high connection strength and airtightness are required. Figure 1 shows a cross section of a part of pin 1 and box 2 that make up the pipe joint, pin 1 is part of an oil country pipe, while box 2 is part of a coupling pipe. It is. As shown in Fig. 1, each of the pin l and the box 2 is provided with threaded parts 3, 3° and a metal seal part 4.4°, which constitute a joint part, and this metal seal part further has a sub-seal part. It is divided into 5.5゛ and main seal part 6,6゛.

In order to increase the connection strength and airtightness of such pipe joints, the area of the metal seal portion (sub-seal portion and main seal portion) is increased, or the shape of the thread is made square.

However, oil country tubing for deep wells usually weighs 8-5 to 14.0 kg.
/m? Since a high pressure of n (5,000 to 20,000 ρsi) is applied, oil country tubular joints are required to have a high degree of airtightness.

Therefore, in general, in order to achieve airtightness sufficient to withstand such high pressure, high surface pressure must be applied to the metal seal and threaded parts, resulting in galling (seizure) at the metal seal and threaded parts. Its occurrence was unavoidable.

On the other hand, in the past, common steel or Cr-Mo steel containing several weight percent of chromium (Cr) and molybdenum (Mo) was used as the material for oil country tubular goods, but as mentioned above, in recent years,
As oil well conditions become increasingly severe, H2S and C
Based on the demand for oil country tubular goods that exhibit sufficient performance such as corrosion resistance even in a corrosive environment accompanied by O2, oil country country tubular goods made of high chromium-containing steel containing 10% or more of Cr are being used. However, such high chromium-containing steels have poor heat dissipation properties, and the occurrence of galling is particularly noticeable, and improvements are desired.

Therefore, in order to prevent the occurrence of galling in oil country tubular joints, especially oil country tubular joints made of high chromium-containing steel,
The surface of the metal seal part is chemically treated with phosphate, oxalate, etc., or an activated metal layer such as Fes Nt, Co, etc. is provided on the surface of the metal seal part and/or the thread part surface, and the upper layer is coated with CuSPb, Sn, etc. It is also known that metals with good ductility can be tempered to improve galling resistance and airtightness (see JP-A-58-31097).

(Problems to be Solved by the Invention) However, in the conventional chemical conversion treatment using phosphate, oxalate, etc., a sufficient treatment film is not formed, and the activated metal layer and its upper layer are coated with Cu, Pb, Known techniques for plating Sn, Zn, etc. require a large number of processing steps and are not easy to work with.

In addition, in the case of products plated with ductile metals such as Cu, Pb, and Sn, Cu, Sn, and Pb will deteriorate under high-temperature, high-pressure environments containing sour gas (H2S, CO2 + water), where high-alloy oil country tubular goods are used. It is easily corroded, which can lead to seal failures in joints and leakage accidents.

Therefore, it may be considered to plate the entire joint joint with a noble metal such as Au, PL, or Pd, which has excellent ductility and corrosion resistance, but this would be extremely expensive and impractical.

(Means to Solve the Problems) In order to solve the problems of the conventional method, the present invention aims to replace only the metal seal portions (sub-seal portions and main seal portions) exposed to the corrosive environment after screw tightening of oil country tubular joints with precious metals. The other threaded parts are plated with Cu, Sn, and P.
The plating treatment was carried out in step b, and the plating layer was used differently depending on the required function, such as where only galling resistance of the oil well pipe fitting is required and where both galling and corrosion resistance are required. It is.

Therefore, the gist of the present invention is to provide an oil country tubular joint comprising a metal seal portion and a threaded portion made of high chromium-containing steel containing 10% or more of chromium, in which the surface of the threaded portion is made of Zn or Sn. , Pb, Cu, and alloys thereof, and the surface of the metal seal portion is plated with gold, platinum group metals, and alloys thereof. This is an oil country tubular joint with excellent galling resistance and corrosion resistance.

That is, in the present invention, Zn, which has excellent galling resistance, is used in the threaded portion of an oil well pipe joint where occurrence of galling is a problem.
Sn, Pb or Cu plating is applied, and the metal seal parts, which are exposed to sour gas environments and are subject to corrosion, are plated with Au, Pd or PT, which have excellent corrosion resistance and ductility. Note that it is sufficient to perform such plating treatment on at least one of the so-called pin side or box side of the oil country tubular joint.

Note that the thickness of each plating layer is not particularly limited, but is preferably about 0.1 to 20 μm. From the viewpoint of corrosion resistance, the thickness of the noble metal plating layer may be relatively thin, but from the viewpoint of galling resistance, it is preferable that the plating layer of Zn, Sn, Pb, Cu, and their alloys be thick.

(Example and operation) As a plating treatment method, electroplating method, ion blating method, etc. are applied, but the usual electroplating method (immersion method) and ion blating method have complicated masking methods and require a large number of steps. There are so many that it is not practical.

However, by employing an electroplating method using a brush electrode, it is possible to easily apply a different type of plating layer to the threaded portion and metal seal portion of an oil country tubular joint.

The attached FIGS. 2 to 4 are schematic diagrams of its implementation, and FIG. 2 shows the brush electrode 12 being brought into contact with the threaded part of the rotating oil country tubular goods 11 (on the bottle side), and the plating liquid being pumped through the pump 13. By applying current between the electrodes, Zn is applied only to the threaded part.
, Sn, Pb, Cu, etc. are plated, and Figure 3 shows the situation in which gold or gold is plated only on the metal seal part of the pin example.
An example of plating with one type of metal in the platinum group, as shown in Figure 4, is a coupling pipe 16 (box side) of an OCTG, in which brush electrodes 12 are separately applied to the threaded part and the metal seal part in the same way as on the bottle side.
This shows a situation in which a different type of plating layer is applied by contacting the two. In each figure, reference numeral 15 is a plating solution storage pan, which serves to collect the plating solution that falls from the brush electrode 12 along the pins or boxes.

By the plating method using the brush electrode described above, Zns, Sn, Cu, ^U, which is limited to the present invention, can be applied to the pin side or box side screw part and metal seal part of the oil well pipe joint part.
Various types of metal plating were applied to a thickness of approximately 10 μm, and a power tight test was conducted on oil country tubular goods (pin side) and campling pipes (box side). The results are summarized in the table below. In the table below, "Cut 1!i113 μm" means that the surface roughness due to cutting surface finish is 3 μm, and "Shot 10 μm" means that the surface roughness due to finishing shot peening is 10 μm. It shows that it was.

The test procedure at this time was as follows.

Outer diameter of tube: 73. Omm Material: 25Cr-5ONi-6Mo-Fe (Strength?
? kgf/mI! l) Main seal taper: 1
/10 Tightening/untightening speed: 0.5 rpm /I2I slipping compound was used. Also, for examination of corrosion resistance, high chromium alloy steel oil country tubular goods (20Cr-35Ni-5Mo-Fe) containing 20% Cr were used.
, strength 77 kgf/m! , outer diameter approximately 60.3mm,
7.1 mm thick) and plated with various metals.
The metal seals were coated with a thickness of μm, and the coupling tube (box) made of the same type of alloy steel was treated in the same manner. After they were screwed together,
20% NaCl aqueous solution, loatm CO2+0.1a
The test was carried out in an environment of tmH2S for 500 hours under the conditions of an additional stress of 0.9 σy and an internal pressure of 600 atm.

The results are shown in Table 2, and it is known that although the Zn and Cu plated metal seal parts are corroded, the precious metal plated parts are not completely corroded.

Table 2 shows the corrosivity (g corrosion rate) of various metal materials, H2
The results of investigating the relationship with changes in the partial pressure of S are shown in FIG.

From this result, it can be seen that Au and Pt have very good corrosion resistance (and it is good to apply them to the metal seal part.

From the above results, it is preferable that the metal seal part, which comes into contact with sour gas in particular, be plated with one of Au, Pt group metals, and their alloys, which have excellent corrosion resistance as well as galling resistance. In addition, the threaded part with little contact with sour gas is made of Sn, which has excellent galling resistance.
It can be understood that plating with metal such as , Pb, Cu, etc. is sufficient.

Therefore, by using different plated metals for each part of an oil country tubular joint according to the requirements for galling resistance and corrosion resistance, it is possible to impart the necessary and sufficient performance to the oil country tubular joint. It is.

(Effects of the Invention) According to the configuration of the present invention, the problems of galling and corrosion of oil country tubular joints can be solved by performing plating to the minimum necessary extent without performing unnecessary surface treatments.

Therefore, for example, when mining from a deep offshore oil field, a large number of oil well pipe joints used can be constructed at low cost, making a great contribution to industry.

[Brief explanation of the drawing]

Figure 1 is a cross section of an oil country tubular joint; Figures 2 to 4 are schematic diagrams of plating by electroplating using brush electrodes on oil country tubular goods; and Figure 5 is a diagram showing the H2S resistance of various metals. It is a graph showing corrosivity. Oil country pipe (bottle) 2; Coupling pipe (box) 3.3': Threaded part 4.4": Metal seal part 5
．． 5': Main seal section 6. 6': Sub-seal section 11: Oil country pipe (pin side) 12: Brush electrode 13: Mechanical liquid pressure pump.

Claims (1)

[Claims] Made of high chromium-containing steel containing 10% or more of chromium,
In an oil country tubular joint having a metal seal portion and a threaded portion, the surface of the threaded portion is plated with one of Zn, Sn, Pb, Cu, and alloys thereof, and the surface of the metal seal portion is plated with gold, platinum group metal. An oil country tubular joint with excellent galling resistance and corrosion resistance, characterized by being plated with metal or one of their alloys.