JPH07332550A - Processing method for improving seizure resistance of oil well pipe screw joint - Google Patents

Abstract

PURPOSE:To provide a method capable of solving a problem of seizure or the like, caused when tightened, by surface treating a contact surface at least with an oil well pipe in an oil well pipe screw joint. CONSTITUTION:In an oil well pipe screw joint 2 provided with a screw part consisting of stainless steel to be screwed to a screw part of an oil well pipe 1 to be connected and a seal part 4 brought into metal-to-metal contact with an end surface in a part beyond a screw part 3 of the oil well pipe 1, at least one of connecting parts of the connected oil well pipe is heat treated in the 18% or less oxygen concentration atmosphere in a condition at 700 deg. or lower heating temperature and for a 5 min or more heating time, to produce an oxidized scale.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving seizure resistance of oil well pipe threaded joints. More specifically, in order to improve seizure resistance, at least the contact surface of the oil well pipe threaded joint with the oil well pipe is provided as a surface. The present invention relates to a method for processing and solving a problem such as seizure that occurs during tightening.

[0002]

2. Description of the Related Art The depth of an oil well reaches several thousand meters, and in recent years,
It is about to reach 10,000 meters. An enormous number of oil well pipes are vertically inserted into such oil wells. All of these oil country tubular goods are used while being connected in series by pipe joints.

In this pipe joint, an axial tensile force due to the weight of the oil well pipe and the pipe joint itself, a ground pressure exerted from the periphery to the outer peripheral surface, a pressing force to the inner peripheral surface by an internal fluid, etc.
Various harsh forces act.

It goes without saying that these forces become more severe as the oil well depth increases. A pipe joint that can be used under such severe conditions is required to withstand a large tensile load and at the same time have reliable sealability.

Therefore, in order to meet the above demand, many proposals have been made in the past.

That is, an oil well pipe threaded joint is generally constructed in a structure that can withstand these loads, and the threaded portion of this screw joint is screwed into the oil well pipe threaded portion, and is screwed where the threaded portion of the threaded joint exceeds the threaded portion. A metal seal portion is formed in contact with the end surface of the thread portion of the oil country tubular good.

Further, referring to FIG. 2, regarding the tensile load resistance, the shape and pitch of the threaded portion 32 of the threaded joint 2 and the threaded portion 31 of the oil country tubular good 1 are improved, and good results are obtained by this improvement. Has been.

On the other hand, regarding the sealing property, when the screw portion 32 of the threaded joint and the screw portion 31 of the oil well pipe 1 screwed with the screw portion 32 are abutted against each other, the metal-metal contact causes the metal seal portion to come into contact with each other. It is formed and the sealing property is secured.

However, particularly in the case of stainless steel, there is a problem of seizure at the time of tightening at the threaded portion and the metal-to-metal contact seal portion.

That is, the seal portion is usually 100 to 2
A high surface pressure of 00 kg / mm ² is applied, and if lubrication at the time of tightening is insufficient, seizure easily occurs at the seal portion.

When this seizure occurs, the seal performance is impaired, and an accident such as a crude oil or gas leak often occurs.

As one of the measures, conventionally, as a method of improving seizure resistance of a seal portion by metal-to-metal contact, as disclosed in Japanese Patent Publication No. 12995/1990, copper, zinc, etc. Coating is performed, or as described in JP-A-63-50462, a seal is produced by irradiating the metal-to-metal contact seal with ionized particles. The surface of the part is modified. With respect to stainless steel, it is generally performed that one of the threaded portion of the threaded joint and the threaded portion of the oil country tubular good is shot-pinned and the other is coated as described above.

However, although such a measure can prevent a fatal accident such as seizure, the seizure resistance of the entire threaded joint is still insufficient. Further, the above-mentioned countermeasures still have the problem that the processing steps are complicated and expensive.

From this point of view, the present invention provides an inexpensive and simple surface treatment method which is excellent in seizure resistance.

[0015]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned drawbacks. Specifically, the seizure resistance of an oil country tubular goods threaded joint largely depends on the surface condition of the threaded portion or the seal portion. If the surface treatment is insufficient, seizure frequently occurs.

However, this surface treatment process is complicated and expensive.

Based on these points, the present invention proposes a surface treatment method for improving seizure resistance in oil country tubular goods joints, and moreover, a surface treatment method which can be easily implemented at a low cost.

[0018]

That is, the method of the present invention is made of stainless steel containing 10% or more of Cr in weight ratio, and the screw portion to be screwed to the screw portion of the oil country tubular goods to be joined and the screw In an oil well pipe threaded joint provided with a metal-to-metal contact seal portion on the end surface beyond the portion, one of the oil well pipe threaded joint and the joint portion of the oil well pipe screwed into the oil well pipe joint, or Both of them are characterized in that they are heat-treated in an atmosphere having an oxygen concentration of 18% or less under a heating temperature of 700 ° C. or less and a heating time of 5 minutes or more to generate an oxide scale.

More specifically, the present inventor first carried out an investigation and study on seizure resistance of a threaded joint in an oil country tubular goods joint made of stainless steel containing 10% by weight or more of Cr.

As a result, it has been found that the seizure property is greatly affected by the surface condition of the screw part and the seal part due to metal-to-metal contact.

In particular, it is effective to generate an oxide scale at the screw portion or a seal portion due to metal-to-metal contact, and use this to adjust the surface condition. When piled up, at least one of the threaded joints was heat-treated under the conditions of a heating temperature of 700 ° C. or lower, a heating time of 5 minutes or longer and an oxygen concentration of 18% or lower to generate an oxide scale.

By adjusting the surface condition in this way, seizure resistance was greatly improved, and an excellent oil country tubular goods threaded joint was obtained.

Then, the present invention will be further described in detail as follows.

First, the inventors of the present invention added Cr in a weight ratio of 10
%, The seizure resistance of the oil well pipe threaded joint made of stainless steel containing more than 100% of the steel was investigated and found that the surface condition of the threaded part of the oil well pipe threaded joint had a great influence.

On the other hand, looking at the surface treatment method as a means for adjusting the surface condition, the surface treatment method using an oxide scale is economical and simple.

From this point of view, when attention was paid to the surface treatment method using the oxide scale and the relationship with the seizure resistance was examined, among the conditions for generating the oxide scale, the oxygen concentration, the heating temperature, and the heating were selected. It was found that time has a strong correlation with seizure resistance.

That is, the seizure resistance of the oil country tubular goods threaded joint greatly changes depending on the conditions for forming the oxide scale, that is, the oxygen concentration, the heating temperature and the heating time.
The reason for this is that the thickness of the oxide scale and the releasability are different depending on the changes in the conditions for forming the oxide scale.

As a result of such an examination, various oxygen scales were changed by changing the oxygen concentration, the heating temperature and the heating time in order to further advance and find out the requirement that should be taken in view of the seizure resistance. When the relationship between the produced oxide scale and seizure resistance was determined, the results shown in FIG. 1 were obtained.

FIG. 1 shows a screw joint at one end or both ends of an oil country tubular good made of stainless steel containing 13% Cr with an oxygen concentration of 2 to 2.
It shows the results of carrying out a seizure resistance test by heating at a heating temperature of 400 ° C. to 700 ° C. in an atmosphere of 1% to generate an oxide scale.

As is apparent from FIG. 1, when the heating time is 5 minutes or more and the oxygen concentration in the atmosphere is lower than 18%, seizure does not occur. On the other hand, the heating time is 5
If the oxygen concentration in the atmosphere exceeds 20% for less than a minute, the seizure resistance is extremely deteriorated.

From such a point, in the present invention, heating is performed at a heating temperature of 700 ° C. or lower for 5 minutes or more, and the oxygen concentration in the atmosphere at this time is adjusted to 18% or lower. When the oxide scale is produced by adjusting in this way, the seizure resistance is kept to a satisfactory level.

If the oxygen concentration is 3% or less, the treatment time becomes excessive, so 3% or more is desirable.

The upper limit of the heating temperature can be increased to 700 ° C. or higher, but at 700 ° C. or higher, the dimensions of each screw part of the joint are apt to change due to thermal strain.
It is preferably 0 ° C or lower. The lower limit is preferably 400 ° C. or higher because the processing time for forming the oxide scale becomes excessive.

[0034]

EXAMPLE As shown in FIG. 2, oil country tubular goods 1 having an outer diameter of 88.9 mm and a wall thickness of 6.45 mm were connected by using a screw joint 2. The composition of the threaded joint 2 is as shown in Table 1,
It is a stainless steel containing 13.1% of Cr. Further, the threaded portion 3 of the threaded joint 2 is heated under the conditions shown in Table 2 to generate an oxide scale, and the threaded portion 3 in which the oxide scale is generated.
The seizure resistance test was performed by screwing the oil country tubular goods 1 onto the.

The results are shown in Table 2.

10 for each oil country tubular goods threaded joint
Tightening and loosening were repeated for several times, and the seizure state in the seal portion and the screw portion was observed.

No. within the preferable surface treatment conditions 1-10
No seizure was observed in any of the oil well pipe threaded joints. Also, after fastening these screw joints, an internal pressure test was conducted.
None of them leaked. The pressure given here is 80% of the pressure at which the inner surface of the pipe yields, and also conforms to the standard value of API (American Petroleum Institute).

On the other hand, in Comparative Example No. Nos. 11 and 12 had heating times shorter than 5 minutes. Since the treated oxygen concentrations of 13 and 14 are higher than 18%, seizure occurs. In addition, No. In Nos. 15 and 16, the heating time and the treated oxygen concentration were satisfied, but the heating temperature was not satisfied, so that the screw dimensions were out of the tolerance and were unusable.

In the embodiment, the example in which only the screw joint is subjected to the heat treatment is shown. However, the present invention is not limited to this, and the heat treatment may be applied to the screw portion screwed with the screw joint in the oil country tubular good. Alternatively, both may be heat-treated together.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

As described in detail above, according to the method of the present invention, when the oil country tubular goods or the oil country tubular goods are sequentially connected through the threaded joints, the oil country tubular goods or the threaded joints are pre-oxidized under a certain control condition. Then, these are connected to each other.

Therefore, since the joint surfaces of the oil country tubular goods and the threaded joint are maintained in proper surface states, problems such as seizure do not occur when tightening.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the treatment conditions and the effect on seizure resistance in the present invention.

FIG. 2 is a cross-sectional view showing a part of the oil country tubular goods threaded joint to be treated in the present invention.

[Explanation of symbols]

 1 Oil well pipe 2 Screw joint 3 Screw part 4 Seal part by metal-to-metal contact

Claims (2)

[Claims] 1. A screw part which is made of stainless steel containing 10% or more of Cr in a weight ratio and is screwed into a threaded part of an oil country tubular good to be joined, and a metal is provided on an end surface of the oil well tube beyond the threaded part. In an oil well pipe threaded joint provided with a seal portion in contact with a metal, one or both of the oil well pipe threaded joint and the joint portion of the oil well pipe screwed to the oil well pipe screw joint have an oxygen concentration of 18% or less. Under an atmosphere, heating temperature is 700 ℃ or less and heating time is 5
A treatment method for improving seizure resistance of an oil country tubular goods threaded joint, characterized in that a heat treatment is performed under a condition of not less than a minute to generate an oxide scale. 2. The seizure resistance improving method for an oil country tubular goods threaded joint according to claim 1, wherein the oxygen concentration of the atmosphere is set to 18% to 3%.