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.