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.

What Are The Important Steps In The Oil Pipe Processing

Pipeline straightening

Generally, pipeline has to go through a number of long-distance or short distance transport, and finally arrived at the use of the site. In the course of transportation and loading, the collision or breaking of the pipe is difficult to avoid. Therefore, in order to make the pipeline construction to meet the acceptance criteria, it is necessary to straighten the pipe. Generally, for manual straightening, the diameter of pipe is smaller than by machine which pipe is straightened with a diameter larger than 50mm , sometimes pipes need to be heated before straightening under special circumstances. When the pipe diameter is larger than 200mm is generally not easy to bend or deform, therefore rarely need pipeline straightening.

Welding

Welding is a main form of pipe connection. There are many kinds of welding methods, commonly used in gas welding, arc welding, argon arc welding, argon itu welding and carbon dioxide welding. Checking whether the tube incision and groove to meet the quality requirements before pipeline welding. Then when nozzle paired, the inner wall should be flushed. Specified requirements, the general pipeline should not be more than 10% of the thickness of the wall, and not more than 2mm; Grade SHA piping should not be more than 10% of the thickness, and not more than 0.5mm.

Groove processing

Groove processing is an effective measure in order to ensure the quality of pipe welding. There are various forms of groove, the selection of groove type should consider the following aspects: 1.ensure the welding quality 2. welding operation is convenient 3. save electrode 4. prevent pipe deformation after welding.

There are several groove types often used in pipeline welding, I-groove, V-groove and U-groove. I-groove applies to welding nozzle which pipe wall thickness below 3.5mm. According to the situation of the thickness, adjust nozzle clearance to ensure weld penetration. This kind of weld, pipe wall without chamfering, actually is no need for processing groove, as long as the verticality of pipe incision can guarantee the requirements, you can direct welding. V-groove is applicable to low pressure pipe welding. The groove of angle is from 60 degrees to 70 degrees and the root has a blunt edge which height is 1 ~ 2mm. U-groove is suitable for high pressure pipe welding. The thickness of pipe wall is between 20mm and 60mm and the root has a blunt edge which thickness is about 2mm.

The form and size of groove processing should be consistent with the specified in the design document. Pipe groove processing should adopt mechanical method, plasma arc and other heat processing method can also be used. After a heat processing method, should remove the oxide skin on groove surface, slag and irregularities should be polished smooth.

Pipe cutting

The purpose of pipe cutting is to cut a section of the pipe with a size requirement. According to the requirements of the specification, different materials of the pipe should be used in different cutting methods. Carbon steel pipe, alloy steel pipe shall be cut by mechanical method. When using oxygen acetylene flame cutting, we must ensure that the correct size and smooth surface. Stainless steel pipe, non-ferrous metal pipe should be used in mechanical or plasma cutting method. Galvanized steel pipe should be with a hacksaw or mechanical cutting. Pipe cutting is an important working procedure, the quality of pipe cut has a direct impact on the next operation incision.

Pipe, pipe fittings cleaning inspection

The pipe should be cleaned and checked before installation. The dirt and impurities should be removed, and the appearance inspection should be carried out according to the current regulations of the country, and the unqualified shall not be used. The inspection of the pipe mainly has the following several points:

• Check the specifications, quantities and marks of the pipe according to the design requirements.
• If the objection to the quality of the book is not resolved, the batch of pipes shall not be used.
• Whether the pipe has cracks, shrinkage, slag, folding, heavy leather and other defects.
• Thread sealing surface, the machining precision and the roughness of the groove should meet the design requirements and manufacturing standards.
• In grade SHA piping, the outer surface of the pipe with the design pressure equal to or greater than 10MPa shall be carried out in accordance with the provisions of the non-destructive testing.

Different Kinds Of Oil Casing Test

Oil casing pipe is a high end product of steel pipe production. There are many kinds of casing, the diameter of the casing is in the range of 15 kinds of specifications and the external diameter of casing is 114.3-508mm. Steel grade is divided into J55, K55, N80, L-80, P-110, C-90, C-95, T-95 and so on; There are different kinds of type and requirements of the casing pipe end button type, the processing button type has STC, LC, BC, VAM and so on. There are many tests in the production and installation of the oil casing, including the following aspects:

Ultrasonic Testing

When the ultrasonic propagates in the detected material, acoustic characteristics of materials and internal organizational changes have a certain effect on ultrasonic propagation. By detecting the extent of ultrasonic affected, to understand the changes in the performance and structure of the material.Radiographic Testing

The amount of radiation from the normal part and the defect is different, according to this, ray detectors can cause differences in the blackness of the negative.

Penetrant Testing

Take advantage of capillary action, penetrant testing will penetrate liquid into the opening on the surface of solid materials, and then imaging agent suction the liquid to reveal surface defects. From the penetration operation to the defect display is relatively short, generally about half an hour, you can test surface fatigue, stress corrosion and welding crack, the size of the crack also can be directly measured.

Magnetic Particle Testing

The magnetic flux leakage of the casing tube defects can adsorb the magnetic particle forming the magnetic mark, so as to provide the defect display. Magnetic particle testing can test the surface and subsurface defects, the defect is easy to identify. Paint and plating surface does not affect the detection sensitivity.

Eddy Current Testing

Take advantage of eddy currents induced by ferromagnetic coil in the workpiece, the quality of the internal workpiece is analyzed. Eddy current testing can test the surface defects of various conductive materials, and can indirectly measure the length of the defect, but it is difficult to control the parameters, and the results are difficult to interpret. What’s more, the object to be detected must be conductive crack.

Magnetic Flux Leakage Testing

The magnetic flux leakage detection is based on the characteristics of high permeability of ferromagnetic materials. Measuring permeability changes due to defects in ferromagnetic materials to test the quality of in-service oil casing.

Magnetic Memory Test

Magnetic memory testing is the relationship between the physical nature of the magnetic phenomenon and the process of dislocation, which has high efficiency, low cost, no need to be polished and so on. It has important and wide application prospects in industry.

Development of magnetic memory testing technology

As we all know, ferromagnetic metal materials as a force structure can withstand fatigue loads in different degrees, so as to cause fatigue crack.

Due to fatigue crack mostly sprouted in the stress concentration region caused by surface defects, adding the stress concentration in the component can cause the material to produce the early damage such as stress corrosion, therefore, it is very important to effectively carry out the test of the surface stress of the component. Because some of the components must be loaded and some of the equipment is complex in the conventional stress testing methods, most of them are not adapted to the non-destructive testing of industrial field.

In 1990s, Russian scholars first proposed that the stress concentration zone of the component surface can be detected by magnetic memory. The magnetic memory testing technology is expected to accurately test the dangerous parts that are characterized by stress concentration. This is a new nondestructive testing method for the early diagnosis of metal components, thus the theory has been paid attention by all the countries in the world.

It is anticipated that, as a new in-service diagnostic methods, magnetic memory testing technology will be further developed through non-destructive testing industry colleagues tireless efforts, for the benefit of human society.

Conclusion

In these tests, there is no specific standard for the magnetic memory testing, yet to be developed. The remaining six kinds have their own testing standards and more mature.

Summary For Casing And Tubing Failure Modes

Casing and tubing is an important material and equipment in the petroleum industry and it has a great amount of use. Casing pipe and pipe string failure will lead to the entire pipe string can not work normally and you will see a lot of casing and tubing corrosion in the construction site. Based on this, the applicability evaluation of casing and tubing with suspected defects is proposed, not only you can make a judgment on the quality of the tubing, but also you can regulate the tubing which doesn’t meet the standards.

The working condition of casing and tubing is relatively poor, and the stress state is complex, so the failure mode is varied, and the failure analysis is summed up in the following 3 types:

Deformation failure

In practical applications, due to the radius of casing and tubing is much smaller than that of the license, instantaneous plastic bending deformation is usually occurred in casing and tubing. It will cause permanent bending of casing and tubing (commonly known as dead bending) in a long time.

In addition, flexible deformation beyond the tensile limit, exceeding the limit of deflated or compressed phenomenon are all part of the deformation failure.

Fracture failure

Fracture failure in the casing and tubing is a large proportion of failure fracture, especially the fatigue fracture that damage is more serious. The main fracture forms are:

• Overload fracture   The speed of pipeline into the wells is too fast, resulting in its snap off when encountered downhole plug or during the job the underground fallen objects lead to pull off and so on.
• Low stress brittle fracture   Brittle fracture of the casing and tubing weld.
• Stress corrosion fracture   Sulfide stress corrosion cracking can be caused when working in oil and gas wells with high sulfur content. The characteristics of the stress corrosion fracture usually have 3 areas, fault source area, crack propagation region, fast break or tearing zone.
• Hydrogen embrittlement   When the tubing material contains too much hydrogen, it’s easy to produce hydrogen embrittlement in tensile force. The characteristics of hydrogen embrittlement fracture are in the fracture edge can be observed in white or white light ring.
• Fatigue fracture and corrosion fatigue fracture   Since the coiled tubing have to constantly import or winding roller, it will be subjected to cyclic stress, and the well often has a corrosive medium erosion. Therefore, the working condition of the coiled tubing subjected to fatigue or corrosion fatigue is the most.

Surface damage failure

Surface damage mainly includes 3 forms:

• Corrosion   Including uniform corrosion (such as in a long time storage process leading to corrosion), pitting corrosion (such as the internal and external appearance pitting in the process of using or storing) and crevice corrosion (such as the corrosion between oil pipe welds and materials).
• Wear   The wear between the downhole tubing and casing or the wear between oil pipe and grip system for injection head and so on.
• Mechanical damage   Casing and tubing in transit surface bumps; The scratch of the wax scraper which falls into the well in the paraffin removal operation; In the injection process because of holding tight, left on the surface indentation.

Measures

Most of the tube failure accident occurred in the transition zone of the thickened transition, which accounted for 70%. The reason of failure is that the structure is not reasonable, resulting in stress concentration and corrosion fatigue. Central tube failure accident accounted for 30%. The cause of failure is the interaction of wall thickness thinning caused by abrasive wear and corrosion pit.


Proposed to strengthen the inspection of the pipe body before welding and deal with the serious internal corrosion to ensure the quality of the tube;
Ultrasonic inspection is carried out around the thickening transition zone of the oil pipe to check whether there is any defect in the transition zone. Length of transition zone and arc radius of oil pipe should be checked before welding, where thickened inner transition zone <100mm, R <300mm are not to be welded;
Strengthen the management of drilling fluid, the pH value of drilling fluid should be maintained at 10 or more than 10 under the condition permission.

Conclusion

With the increasing demand of the drilling industry, the oil pipe is easy to damage under the long-term high temperature and high pressure and unexpected accidents are common occurrence. So it is urgent and important to analyze the failure of tubing. Timely measures can improve the utilization of resources, avoid economic losses, and bring greater social and economic benefits.