How To Carry Out Pipe End Machining

What is pipe end machining

Pipe end machining is that the process of pipe thread, sizing, thickening, strengthen the heat treatment, chamfering and other processes are carried out on the end of pipe. Each process is quite important for carrying out the pipe end machining, let's look at all the processes together.

Pipe end thickening

Pipe end thickening is mainly used for the oil pipe and geological tube. Since the pipe wall will be thinned after the end of processing, the part of threaded connection has become the weak link of the whole pipe body. In order to improve the strength of the connecting part of the thread, the method of pipe end thickening is adopted to increase the wall thickness of the pipe end. There are 3 forms of pipe end upsetting, internal upsetting, external upsetting, internal and external upset.
The process of pipe end thickening is:
pipe end heated→thickened→cooled→checked.
According to the size of the thickened tube, the thickness of the form and the amount of thickening of the compression, the number of heating and thickening is not the same, there is one heating one thickening, or two thickening one heating. In order to eliminate the phenomenon of uneven performance of the thickened end and the pipe body caused by the thickening, the steel pipe usually does integral heat treatment after thickening.

API steel grades for tubing and casing

API standards for Casing and Tubing

API, shorted for American Petroleum Institute, is considered as one of the most authoritative and comprehensive principles for oil and gas industry. Products complied with API standards are always thought of reliable quality. Under the general standards, there are some subordinated specifications drafted for each specific OCTG product, such as API 5B, API 5CT, API 5D, API 5L and so on.

API 5B and 5CT are mainly used for tubing and casing, standardizing the chemical properties, steel grades, manufacturing methods, color coding, heat treatment, inspection, etc. Tubing and casing are supposed to withstand specific pressure in transportation of oil or natural gas, which means the steel material should have proper yield strength, therefore API 5B and 5CT lay specific standards of steel grade for tubing and casing to meet the general application purpose.

Color codes for API steel grade

In order to clearly distinguish the steel grade, tubing, casing and its coupling should be painted with color codes respectively. Color bands should be painted on tubing and casing body longer than 600mm to either end. The whole outer-body of the coupling needs to be painted color and then color codes.

API 5B and 5CT provide various steel grades and color codes of each grade, offering detailed and overall information of casing and tubing, which help you clearly pick out the most suitable products for different well application.

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Quality Inspection Of Seamless Steel Pipe

Seamless steel pipe is one of the important products in OCTG products. It is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, automobile transmission shaft, bicycle frame and construction of steel scaffolding and so on. Comparing with the other steel pipe, seamless steel pipe has stronger anti-bending and torsional ability under the condition of the same cross section area. It is widely used in the national economy, and is entitled to the "industrial blood vessel". Therefore, the quality of seamless steel pipe has very demanding requirements.

Seamless steel pipe inspection generally include: inspection geometry, surface quality; test chemical composition, mechanical properties, process performance, high and low times of the organization; NDT inspection; some special performance inspection and weighing length measurement. Let’s look at some relatively important quality inspection together.

 

Seamless steel tube geometry inspection

• Seamless steel pipe wall thickness inspection    Micrometer is the main tool that is adopted. When you check, left hand holds the micrometer stand, with right hand rotation induced wheel, and the wire rod should be coincident with the diameter of the measuring point. Once found that the wall thickness is not qualified, it should be marked in time.
• Outside diameter, ellipse of seamless steel pipe inspection    Calipers, vernier caliper should be taken. The caliper should be perpendicular to the axis of the steel pipe in checking, measuring the maximum and the minimum point when the pipe rotated slowly. Founding the outer diameter of large or small, you should mark it in time.
• Seamless steel tube length inspection    The steel tape can be measured directly by metallic tape.
• Bending inspection of seamless steel tubes    With the tools of level, feeler and line.
• End profile inspection    At two ends of the steel tube should be cut into specified angle and remove burrs. The method of inspection adopts angle square and general use tube end groove clamp in the field.

Mechanical properties and process performance check of seamless steel tube

In order to verify the mechanical properties of seamless steel pipe to meet the requirements of the standard, the test sample of seamless steel pipe mechanical performance should be prepared carefully. Mechanical property test includes tensile strength, yield strength, elongation, impact energy and so on. Process performance test includes flattening test, flaring test, hydrostatic testing, curling trials, cold bend test, perforation test. These test items are based on different standards and different uses of seamless steel tubes.

Non-destructive testing of seamless steel pipe

Under the premise of not damaging the specimen, NDT refers to carry out inspection and testing to internal and surface structure, properties, status of specimen with physical or chemical methods, advanced technology and equipment. The development of non destructive testing technology has experienced three stages: Nondestructive detection, nondestructive testing and nondestructive evaluation.

Nondestructive detection is the name of the early stage, and the meaning is to detect and detect defects; Nondestructive testing is the name of the current stage, its meaning is not only to detect defects, but also to detect some other information, such as the structure, nature, status, etc.; And nondestructive evaluation (NDE) is one which is entered or is entering a new stage, it requires not only the defects are found, but also detection test pieces of the structure, properties, status, and access more comprehensive and more accurate, comprehensive information, such as defects associated with the shape, size, location, orientation, inclusions, tissue defect, residual stress force of information. It is necessary to combined with imaging technology, automation technology, and computer data analysis and processing technology, and mechanics of materials, and other fields of knowledge, and gives a comprehensive and accurate evaluation of the quality and performance of the test piece or product.

Pipeline welded joint design

In practical industrial application, line pipes are always welded to join together to form longer ones to meet the needs of engineering project. The welding joint is supposed to be as strong as the base material, not subjecting to fatigue, bending, crack or other defects.
The most commonly-used type of pipeline joint is butt joint, a process in which two pieces of pipes are joined together in the same horizontal plane. Butt welding has the advantage of good tolerance, high strength and less needed material. However, butt welding doesn’t mean the simple face-to-face connection of two pieces, which means the joining surface are not always vertical to the pipe plate. The edges of pipes are processed into different angles before welded, that’s what called pipeline beveling.

What is pipeline beveled end and why use it

Beveled end, to put it simply, is a joint surface with a specific beveled angle. In fact, it is processed prior to the welding of two pieces of line pipes, an angle formed at the edge of the end of the pipe with the help of a beveling machine.
Its foremost use is to achieve the best butt welding joint. Some pipes, especially those with great wall thickness, are difficult to be welded together due to low penetration. Even if joined together, they may not be deeply and completely welded due to the great thickness, so potential welding defect remains. Thus, when both ends of the pipes are beveled to form an angle, the thinner walls make it easier for pipes to be jointed together. Some filler materials will be put in the beveled space. The bevels increase their contact area, guaranteeing a better and deeper welding effect. Besides, pipeline beveling can be used to deburr the cut ends, making the pipes neat and tidy.

Common types of beveled ends and comparison among different types

Beveling ends can be made into various angles, achieving the better welding seam. Common beveled ends for butt joints are I-Type butt joint, single-V beveled end, double-V beveled end and single U-beveled end.
Beveled angle refers to the angle between the two beveled surfaces. Beveled face angle, normally used for single-U type, refers to the angle between the beveled surface and the vertical line to the pipe itself. The root opening refers to the gap between the roots of both pieces before welding, to ensure the roots get complete welding. The root radius for single-U beveled end is to increase the transverse space between the roots, making the welding reach the bottom of the root.

• I—type butt joint, also called square butt joint, is a relatively simple joint method for pipes of 1 to 6 mm in thickness. Strictly speaking, it is not a beveled end joint, for it only requires parallel matching the edges of two pieces together without certain angles. It is easy and economic to process, but is not recommended for pipes of thick walls.  As for thicker wall pipes, the angle of the bevel ends needs full consideration, trying to use the least filler metal material to provide the desired welding soundness.
• Single-V beveled end, is the most widely-used butt joint type in pipeline application. It suits pipes with the thickness of 3 to 26 mm. The beveled angle should be approximately 40 to 60°. Single—V beveled end is processed by a beveling machine. Comparatively speaking, it is more costly and needs more filler material than the I—type butt joint, but the joint is much stronger than the square joint. The disadvantage of single-V beveled end is its easy subjection to angular deformation.
• Double-V beveled end, also called X—beveled end, is developed on the basis of single—V beveled end. It needs double-side welding, so the material needs to be turned over after welded one side and the preparation time is longer than the single-V beveled end. It can be used for pipes of thickness 12 to 60mm. For pipes of same thickness, a double—V beveled end requires less filler metal material, because there are two narrower V-joints compared to one wider single—V beveled end.
• Single-U beveled end is a one-side welding joint. It requires less filler metal material than double—V beveled end and is less subjective to deformation. However, due to the radian shape, it is more difficult to process than the former methods.

Anson provides you pipelines with beveled ends

Different types of beveled ends have different requirements on pipes and welding methods. As a professional pipeline supplier,
Tianjin Anson International Co., Ltd provides beveling service according to your requirement. Clients can choose pipes with the most suitable beveled ends before welding application to achieve better pipeline butt welding performance.