JPH1182829A - Friction welding tube fitting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make sealed areas metallurgically connectable by giving surface treatment only to the threaded part of the tube fitting and not coating or applying lubricant to the conical surface and the end conical surface crossing the conical surface including a pin and a box. SOLUTION: Tapered male thread 3 is machine processed on one of the ends of a tube body and a conical surface 4 and a conical recessed surface 5 crossing the comical surface 4 is machine processed on the tip of the male thread 3. A female thread 3' fitting the male thread 3 and a conical surface 4' corresponding to the male thread 3 tip shape and a conical recessed surface 5' crossing the conical surface 4' are machine processed on the box 2. In order to prevent seizure caused by tightening, the threaded part 7 of the box 2 is provided with a metal plating of Zn, Sn, Cu or the like, or a phosphate film coating, or a a special coating allowing to tighten it without lubricant by dispersing a molybdenum disulfate in the resin, but the end part of the box 2 where there is no thread is not given a surface treatment. The pin where there is no thread is also not given a surface treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe joint for friction welding, which is mainly applied to a line pipe joint used for oil and gas transportation. The present invention relates to a pipe joint for friction welding provided with a structure capable of realizing strong friction welding at a metal contact portion on a female inner peripheral surface.

[0002]

2. Description of the Related Art Conventionally, a line pipe joint is usually provided with a groove at a pipe end and butt-welded on site. However, it takes a long time for welding work, and the material quality of a joint due to welding is deteriorated. Also, in the case of high alloy pipes that are suitable for corrosive environments, mechanical joints that can be quickly worked and that do not deteriorate the material of joints are being sought due to problems such as a mismatch in strength between the base metal and the weld metal.

[0003] On the other hand, various types of screw joints having a metal contact type airtight mechanism for preventing leakage of internal fluid are applied to oil country tubular goods (tubing) for collecting oil and gas from wells. It is considered possible to use the joint structure as it is as a line pipe joint, but if the seal remains mechanically pressed, if the internal fluid leaks, the line pipe immediately leads to environmental pollution. There is a problem that cannot be adopted.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a line pipe and a metallurgical joint, not a metal contact mechanism, at the seal portion while maintaining the quick workability of the screw joint. It is intended to provide a joint such as an oil country tubular good.

[0005]

Means for Solving the Problems An oil country tubular good screw joint is repeatedly tightened, but the male screw side (pin) and the female screw side (box) fitting contact portions are usually plated or coated. In addition, when used, compound grease containing metal powder is applied to prevent seizure. The present invention is based on the idea of actively utilizing this burn-in phenomenon.

[0006] In brief, in a threaded joint of a pipe in which a box having a female thread on the inner surface and a pin having a male thread on the outer surface are screwed, a conical surface, a vertical surface of the tube axis, and an inner surface thereof are formed at the threadless tip. The pin side composed of an end conical surface with a concave inclination angle, a screwless conical surface provided on the screw inner part corresponding to the pin tip shape, and an outwardly convex end conical surface intersecting it For the joint member consisting of the box side composed of: To prevent seizure at the time of fitting to the screw part, plating as the above-mentioned seizure avoidance processing,
Apply a surface treatment such as coating, but do not apply plating or lubricant to the conical surface and the conical end surface that intersects with the pin and box. Make it easy to wear.

[0007] When the joint is tightened, the pins and the screws of the box are fitted until the conical surfaces come into contact, and the pins are smoothly screwed into the box to perform the function of aligning the end press-contact parts. When the outer conical surface at the tip of the pin starts to contact the inner conical surface at the back of the box, the inner and outer diameters are machined in advance so that both conical surfaces are tightly fitted. Larger friction heat is generated at the contact surface due to relative slip. At the same time, the oxide film that interferes with crimping is destroyed and the new metal surfaces come into contact with each other, causing sufficient frictional heat and plastic flow at the interface to excite the energy required for adhesion, and tightening the joints Complete. When the tightening is completed, the sliding of the contact surface stops, and the pin tip comes into contact with the corresponding inner end surface of the box. This contact surface has an inclination angle θ with respect to the pipe axis.
Due to the structure having (°), the tip of the pin tends to spread outward along this inclination angle, exerting an action of strongly pressing the conical surface in which the adhesion energy has been accumulated, and the pressure welding step is completed. In this structure, the frictional heat generated by the friction welding and the action of applying a strong pressing force immediately thereafter are satisfied.

The crimping portion of this joint does not cause relative displacement between the pin and the box in the axial direction, the radial direction and the circumferential direction even during use due to strong tightening. It is firmly restrained from surroundings so that it does not act. As another seal, a packing insertion groove is formed in the box screw, and a resin seal packing ring is inserted into the groove when tightening. During the screw tightening process, the seal packing is compressed and rolled in the gap between the male screw and the female screw to fill the slight clearance of the screw, thereby achieving a sealing effect.

With the above-described configuration, the joining of the line pipe is completed, a strong metallurgical joint is provided for the internal fluid, and a seal is secured with resin packing against the external seawater. A mechanical line pipe joint which is excellent in quality and does not involve deterioration of the material due to welding heat input can be provided.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A pipe joint for friction welding according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a fitting state of a pipe joint for friction welding according to the present invention. In FIG. 1, a tapered male screw 3 is machined at one end pin of a tube main body, and a conical surface 4 and a conical concave surface 5 intersecting with it are machined at the tip. In box 2,
A female screw 3 ′ to be fitted to the male screw 3 is machined, and a conical surface 4 ′ and a conical convex surface 5 ′ intersecting with the conical surface 4 ′ are machined so as to correspond to the tip shape of the male screw 3. In order to prevent seizure due to tightening,
Metal plating of Zn, Sn, Cu, etc., or phosphoric acid film coating, or molybdenum disulfide dispersed in resin, and special coating (see JP-A-7-86616) that can be tightened without lubrication are applied. However, the screwless end 8 of the box 2 is not subjected to these surface treatments. No surface treatment is performed on the pin, nor on the outer peripheral portion corresponding to the screwless end 8. Further, a seal packing groove 9 is formed in the box screw, and a resin seal packing 6 is inserted before tightening.

Next, the sealing property of the screw joint according to the present invention will be described. By screwing, the pin tip conical surface 4
Comes into contact with the corresponding conical surface 4 'on the box side, and as the tightening proceeds, the relative sliding length and surface pressure of the contact surface increase, and the pin tip surface 5 comes into contact with the conical surface 5' at the back of the box. To complete the tightening. At this time, by further applying a torque to the contact portion, the pin tip 10 tries to climb on the conical surface 5 ′ along the angle θ, and a high pressing load is applied between the conical surfaces 4 and 4 ′. generate. In FIG.
The relationship between the relative sliding of the conical surfaces 4 and 4 'and the pressing load is schematically shown.

On the other hand, the seal packing 6 is continuously compressed and rolled by a pin screw to fill the screw clearance of about two ridges before and after the insertion portion, and blocks seawater entering from the outer surface through the screw clearance. Also, when applying compound grease for lubricating the screw portion, a small amount is applied to the screw portion span 7 of the pin, and is not applied to the inner surface of the box at all. In this way, compound grease is prevented from contaminating the crimped portion by tightening the screw, and at the same time, the pressure increase of the grease sealed in the crimped portion and the resin packing is suppressed,
Prevents extra pressure on the box and pins. If a special coating treatment can be performed instead of the compound grease described above, and if the same effect is exhibited, it is an optimal means from the above-mentioned viewpoint.

[0013] In applying the pipe joint for friction welding according to the present invention, the main purpose is to apply to a line pipe.
Needless to say, the present invention is sufficiently applicable to a place where perfect airtightness is required, such as an oil country tubular good.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Regarding a pipe joint for friction welding according to the present invention,
Workings, experiments, and results obtained by the present inventors will be described with reference to examples. API standard, X-65 grade, outer diameter: 324 mm, wall thickness: 12.7 mm. A threaded joint made by cutting a buttress according to the API standard on a steel pipe. Taper:
1/10, diameter interference allowance: 1.2 mm, pin tip length: 2
The box is formed with a packing groove having a width of 5 mm and a depth of 2 mm at the complete screw fitting position of 70 mm from the end of the tube, and a width of 4.4 mm and a thickness of 3.3 mm.
mm of Teflon packing was inserted, molybdenum disulfide was dispersed in a polyamide resin in the box, and a special anti-seizing coating coated with the molybdenum was sprayed onto the box to tighten the joint. In this tightening, the metal contact part of the pin and the box was immediately polished with paper to remove rust on the surface, and then degreased with acetone.
Tightening was performed with a load of −m. After this tightening work,
When the joint was cut in the longitudinal direction and the state of adhesion of the fitted cross section was examined with a microscope, a fused portion was clearly observed at the metal contact portion. In another sample, a leak detector was connected behind the metal contact portion, and an airtight test was performed on only the metal contact portion with nitrogen gas at a yield pressure of 80%, but no leak was detected.

[0015]

As described above, the pipe joint for friction welding according to the present invention does not perform any surface treatment on the contact portion so as to positively cause seizure of the metal contact seal portion. Strong metallurgical bonding against internal fluids by applying the basic process of pressure welding, which is a function, to the fitting itself, adopting a resin ring packing for the outer surface seal, and applying a special resin coating that does not require grease. The seal is secured with resin packing against external seawater, and it has excellent workability.
Further, it is possible to provide a mechanical line pipe joint which does not involve deterioration of the material due to heat input by welding.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a pipe joint for friction welding according to the present invention.

FIG. 2 is a view showing a change in a relative slip and a contact surface pressure at a metal contact portion which occurs when a pipe joint for friction welding according to the present invention is tightened.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pin 2 ... Box 3 ... Male screw 4, 4 '... Metal contact crimping surface of pin and box 5, 5' ... Contact surface of pin and box 6 ... Resin ring packing 7 ... Box (and pin) seizure prevention surface Processing section 8: Area where surface treatment and lubrication are not performed 9 ... Box resin packing insertion groove 10 ... Pin screw end

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kunihiko Okamura 2-6-3 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Corporation

Claims (3)

[Claims] 1. A pipe joint for screwing a box having an internal thread on an inner surface and a pin having an external thread on an outer surface, wherein a conical surface 4 is provided at a threadless tip portion, and a slope which is concave inward with respect to a tube axis vertical surface. A pin 1 side composed of an end conical surface 5 having an angle θ, a screwless conical surface 4 ′ provided at the screw inner part corresponding to the shape of the pin tip, and an outwardly convex end cone intersecting the same. The joint member consisting of the surface 5 'and the box 2 side is subjected to a surface treatment such as plating or coating on both the pin and the box, or only on the threaded portion of the box, and the conical surface and the end conical surface intersecting therewith. Has a pin,
A pipe joint for friction welding, characterized in that the box has a structure in which plating, coating or lubricant is not applied. 2. A pipe joint in which a box having an internal thread on an inner surface and a pin having an external thread on an outer surface are screwed together. A pin 1 composed of a pipe end face 5 having an angle θ;
For a joint member composed of a screwless conical surface 4 ′ provided at the back of the screw so as to correspond to the pin tip shape, and a box 2 side composed of an outwardly protruding end conical surface 5 ′ intersecting therewith, Both the pin and the box, or only the screw part of the box, are subjected to surface treatment such as plating and coating,
The conical surface and the end conical surface intersecting with it have a structure in which neither the pin nor the box is plated, coated or lubricated, and a packing groove is formed by processing a part of the groove portion of the internal thread of the box, and a resin groove is formed on the groove. A pipe joint for friction welding, wherein a seal packing ring is inserted. 3. The mechanical joint according to claim 1, wherein a special resin coating having a self-lubricating function is applied to the joint of the pin and / or the box.