Repair characteristics and technology of perforati

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Repair characteristics and technology of perforated gun barrel in oil and gas fields (Part 1)


in oil exploration, perforated gun barrel used in oil and gas fields has particularity that other metal structures do not have: perforating charges or explosives detonate in the gun barrel at a certain depth underground, producing instantaneous high temperature and strong impact, penetrating the perforated part of the gun barrel, and then penetrating the rock stratum or oil and gas reservoir, so as to achieve the purpose of oil and gas well perforation. Therefore, the relevant departments have strict requirements on the use of gun barrels, and clearly stipulate that the use of gun barrels is one-time. Once perforated, they will be used as scrap products or degraded. At present, most domestic oil and gas field perforating guns use imported gun barrels from the United States and Japan, which are expensive, with a height of more than 500 yuan per meter. Its material has poor weldability, serious hardening tendency and great crack sensitivity. So far, there is no precedent for repair and no research report on repair technology. With the determination to actively try and explore boldly, we used manual arc welding to repair the abandoned barrel in the logging and perforating industry of oil and gas fields, breaking through the forbidden zone of barrel repair. The quality of the 114 mm 7.72 mm 2 m gun barrel repaired and welded has been inspected and recognized by the quality supervision, inspection and testing center of oil and gas field perforating equipment of China National Petroleum Corporation

1 repair characteristics of perforating gun barrel

1.1 overview of perforating gun barrel

q perforating gun is a g41350 steel pipe imported from the United States, with a specification of 114 mm 7.72 mm 2 m, and its material is similar to 35CrMoA in China

the barrel after perforating operation is shown in Figure 1. The perforations are distributed on the surface of the whole barrel, arranged regularly, and the diameter of the perforations is different, but they are all 10 mm

Figure 1 Schematic diagram of gun barrel perforation

1.2 analysis of welding characteristics of gun barrel

the material of gun barrel is low-alloy high-strength structural steel (also classified as chromium molybdenum heat-resistant steel), and the average carbon content in steel is as high as 0.35%. Due to the Cr and Mo alloy elements, the hardness of steel is increased. See formula (1) for the carbon equivalent formula and calculation results that reflect the hardening tendency of alloy structural steel recommended by the international welding society


based on this, it is judged that the barrel has a high tendency of hardening and cold cracking, and the weldability is extremely poor. In the welding process, when the temperature of quenching zone is AC3 line, due to the thermal cycle of arc and excessive cooling rate, austenite is easy to transform into brittle and hard high carbon martensite structure, with a great hardening tendency (600hb ~ 700hb), which increases the brittleness of welded joints and intensifies the formation and generation of HAZ (heat affected zone) cracks. At the same time, even if the alkaline low hydrogen electrode is used, the hydrogen content in the weld metal is also up to 6.8 ml/100 g, which is very easy to produce hydrogen induced cracks under the action of welding stress. Therefore, it is necessary to take corresponding control, adjustment and protection during the welding process, before and after welding, so how to distinguish the bandwidth of a system and the bump of sampling rate? Measures to prevent cracks

1.3 design requirements for gun barrel repair

when improving the industrial system to ensure that the chemical composition of the gun barrel matrix is subject to the minimum loss during welding, it is required to conduct a hydraulic test under the condition of 30 MPa, with a constant pressure of 30 minutes, and the gun barrel has no leakage and the gun body has no deformation; The welded joint shall be free of cracks, and the inner wall of the gun barrel shall be free of welding penetration and overlap. During perforation operation, the perforation must be punctured from the original hole position, and the alignment rate between the gun body perforation hole and the original hole is 85%

2 preparation before welding

2.1 groove design and processing

in order to meet the design requirements and achieve the purpose of perforating operation, special structural forms are adopted during repair: first, all holes with irregular shape and size on the original barrel are uniformly processed into holes concentric with the original hole and with the same diameter (10 mm) on the drilling machine, and then concentric 14 mm holes are drilled on the 10 mm hole. The drill must not drill through, and finally drill large holes with concentric 16 mm on the surface layer, The drilling depth is 4.72 mm. In this way, a 10 mm, 14 mm and 3 mm circular platform is formed at the root, as shown in Figure 2

Figure 2 groove structure figure

in order to ensure that the alignment rate between the gun body perforation and the original hole is 85% and the processing is convenient, Q235 (14 mm) round steel with low strength grade is selected, and processed into a 10 mm, 14 mm and 3mm Round block plate (Figure 3) on the lathe, which is placed at the root of the groove, deliberately making the root not fully welded, creating conditions for puncture and perforation

Figure 3 Schematic diagram of plugging plate

2.2 formulation and release of cleaning of gun barrel guidelines for major short board equipment projects in 2018

after perforation operation, the gun barrel is often attached with a thick layer of dirt formed by crude oil and sand, which should be completely removed before welding, and carefully cleaned within 2.03 M around the groove to expose metallic luster; The groove processed on the drilling machine and the blocking plate processed on the lathe will inevitably be stained with oil. It can be cleaned with cleaning agent. After cleaning, it must be dried immediately and transferred to the next process as soon as possible to prevent rust

3 welding process

3.1 welding method and equipment

when repairing the gun barrel, due to the particularity of its groove form, it is best to adopt skilled and flexible manual arc welding method. In order to prevent burn through and weld beading, manual TIG welding can also be used for priming, and then manual arc welding can be used for filling and covering. At the same time, in order to meet strict welding process requirements and obtain excellent welding joints, American Miller DC power supply is selected

3.2 welding materials

the root of the groove is a 35crmoa+q235 dissimilar steel welding joint, which has a large difference in strength level, and it is difficult to weld. The system shows the calibration zero point. In order to make the weld metal have good crack resistance, so as to obtain an excellent welding joint, e4315 welding rod is selected for priming, and E5015 welding rod is used for filling and covering. After baking at (350 ~ 450) ℃ for 2 hours, the welding rod shall be put into a 100 ℃ incubator for insulation, and it shall be taken as soon as it is used. When it is used, an insulation cylinder must be used

3.3 welding parameters

according to the groove shape and the performance of the welded joint, select the process parameters as shown in Table 1, and try to select the lower limit of the parameters. The power polarity is DC reverse connection

Table 1 welding parameters

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