Oil and gas well casing damage and repair

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Oil and gas wells are fixed assets of an oil and gas company, and the formation casing is the most basic element of an oil and gas well. Once the oil formation casing is damaged and cannot be repaired, it means the scrapping of the oil and gas well and the loss of fixed assets. The oil formation casing is subjected to high pressure and erosion of gas and liquid media, and is repeatedly subjected to external forces such as well repair operations and production enhancement measures. The causes of damage are mainly the following.
(1) Poor quality and low strength of the casing itself.
(2) Poor cementing quality and poor sealing.
(3) Corrosion by water, chemical agents and microorganisms
(4) Geological movement and lithology around the casing
(5) damage to the casing by high-pressure water injection
(6) The influence of oil, gas and water wells out of sand.
(7) The damage to the casing caused by improper construction of well repair operations.

There are three general forms of casing damage, namely casing reduction, casing rupture, and casing breakage.

Due to the different casing damage location and damage degree and damage condition, some can not be repaired, some can be repaired.

The repair method for casing shrinkage is to gradually expand the inner diameter by adding pressure to the drill pipe through the roller shaper, which is enlarged step by step during repair. This method is simpler and easier to see results.

For the repair of casing rupture, with seam or hole, there are several methods as follows.

(1) Squeezing cement slurry. When the formation pressure is not large, rupture and leakage is not serious, the method of squeezing cement slurry can be used to repair. The process approach is: first 8 to 10 mm smaller than the casing inside diameter through the well gauge through the diameter, and then in the appropriate location under a suspended plugging device (tool name called bridge plug), the break below the wellbore temporary seal off, and then inject a certain amount of cement slurry above the bridge plug, so that it solidifies into a cement plug, cement plug after solidification, drilling open the cement plug in the casing, and test pressure to check the quality of the cement seal break, to confirm the quality of seal After confirming the quality of the seal, drill open the suspended plug (bridge plug) and flush the sand to the bottom of the well. The casing repaired by this method can generally withstand a pressure of 40 to 80 MPa, but the well should be protected by a packer to avoid high pressure in the section when the well is under high pressure construction.

(2) Casing replacement. When the rupture location in the upper part of the well, and can be inverted to remove the casing above the break, the inverted buckle method can be used to bring up all the casing above the accident section, re-enter the new casing, and tighten the good buckle. The advantage of this method is to ensure the consistency of the casing inside diameter, and the downhole tools can pass smoothly after operation; the disadvantage is that the tightness of the casing buckle downhole is not as tight as at the wellhead.

(3) Subsidy method. The subsidy method is to paste a layer of thin-walled tubing on the inner wall of bad casing to achieve the purpose of repair. The process principle is: in a special high-pressure rubber cylinder set with bellows (thin-walled tube) down to the well casing damage location, holding pressure to make the rubber cylinder expansion, while expanding the bellows, so that the bellows close to the casing damage at the inner wall, and by the adhesive to the casing and bellows adhesive into one, to be cured adhesive, active drilling tools, the high-pressure rubber cylinder removed. This subsidy process is simple and safe to operate.

The well with broken casing can be repaired separately in three cases. The first one is broken but not misaligned; the second one is broken but not seriously misaligned; the third one is broken and seriously misaligned, even the next section of casing cannot be found.

In order to obtain the displacement of the casing after fracture, misalignment depth, the relative distance between the upper and lower fracture and whether the fracture is deformed and other information, can be used to hit the lead seal, instrument testing and other methods to clarify the situation.

For broken casing without misalignment, water mud injection method can be used to repair; for broken but not seriously misaligned casing, such as allowing the replacement of casing, then use the replacement of casing method to repair; such as not having the conditions of the replacement of casing can be used under the repair of the connector, that is, the broken casing grinding and milling off a section, the middle of the upper and lower casing clamping, pulling the tool to ensure that the well can be normal production.

For wells with serious misalignment after fracture and cannot find the next section of casing, the side drilling method can be used to deal with. In other words, the borehole at the fracture is cemented shut, and a borehole is re-drilled with a small drill pipe from the upper casing, and a smaller casing than the original casing is put into the borehole to complete the well.

Oil casing connection problems

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In the working process of the screw pump, the rotor rotation will trigger the twisting and vibration of the oil pipe. In addition, the J-groove of the tubing junction is subject to high friction during the extraction process, which is where most of the tubing damage and deterioration problems occur. At the same time, operators have been looking for a “magic tool” that can improve the casing torque rating and reduce costs at the same time. With the DTR tool, casing connection is no longer a problem! DeltaTORQ Rings (DTR) is a new casing connection kit designed specifically for the upstream oil and gas industry to increase the torque load of casing clamps. The DTR makes perfect use of the J-groove in the casing joint, providing excellent sealing performance in addition to increasing the torque rating of the tubing. The use of the DTR tool eliminates the need for other tools and greatly simplifies the screw pump completion operation. At the same time, the tool is perfectly embedded in the J-slot, making the inner surface of the tubing smoother and reducing frictional losses. The DTR is available in various sizes to meet all casing requirements in accordance with API-5CT standards. During field operations, DTRs are installed by specially designed handheld tools and are calibrated after connection, improving efficiency and reliability. In addition, if the field operation time is tight, DTR can also be installed inside the oil casing in advance without affecting its own reliable working performance. It can be said that the DTR tool brought by Volant has greatly reduced the risk of casing docking problems.

Operational Problem 1 When casing or tail pipe rotation is required, casing designed according to standard API torque standards usually cannot meet the operational torque requirements, which is one of the most frequent and persistent problems in the field. Solution: The DTR is designed to make full use of the J-shaped space at the casing joint. The tool has a high cross-sectional area, which can significantly increase the torque carrying capacity of the oil casing junction hoop, thus improving the operating capacity of the entire string.

Operational challenge 2 The rotor of a cavity pump rotates in the opposite direction of the tubing threads, so it is very common for the tubing to back out during cavity pump operation, and if not detected and resolved in time, the tubing will eventually fall off, resulting in costly workovers. Solution: The DTR can be perfectly embedded in the tubing kink, increasing the torque level and greatly reducing the chance of tubing uncoupling, which is of great value in improving stability, reducing the number of well repairs and increasing production revenue.

Operational challenge 3 As the tubing is used more often, the threads become more worn and eventually thread damage (such as penetration) occurs. To solve such problems, operators must cut and regrind the threads, which undoubtedly increases development costs. For this reason, developers have been actively looking for solutions to mitigate thread wear. Solution: DTR can provide long-lasting protection to the tubing knotting hoop, ensuring reasonable torque and keeping the threads in the best connection condition, effectively extending the life of the tubing.

Operational challenge 4
During the production process of oil ring, the oil pipe is often filled with high-speed flowing gas, sand and other substances, which directly accelerates the wear of J-shaped groove at the oil pipe connection (due to the groove, the smoothness is poor) and reduces the service life of the oil pipe. Solution: DTR makes the J-groove embedded in the tubing junction more smooth, effectively reduces friction, protects the junction and extends the service life of tubing. MLT protection ring, specially made for oil casing connection! MLT is designed to meet the API standard and can play a great role in improving the success rate, whether it is a downstream casing operation or a cementing operation that requires rotary operation. With MLT, field work is so easy.

The problem: Tubing The top drive screw pump is driven by a shaft that connects the surface drive to the downhole screw pump, which usually rotates in the opposite direction of the tubing thread connection, which can cause tubing backing problems and necessitate workovers. Solution: Placing the MLT at the tubing kink can improve the thread torque rating, prevent backbolts, and reduce the use of other equipment, which saves money and increases the life of the tubing. In addition, MLT prevents sand from collecting in the kink, which keeps the threads clean and extends the life of the tubing. Operational challenge: tubing threads We know that tubing connections are made very quickly during field operations, sometimes causing problems such as excessive torque and thread damage. As the number of times the tubing is used increases, the threads become more worn, and eventually the threads have to be removed or reground. There was nothing much many developers could do about the problem, but now the situation has changed dramatically because of MLT. The solution: Volant’s MLT protection ring acts on the knotted hoop to provide protection during the thread connection, keeping the thread butt in ideal condition and effectively preventing excessive torque, which has many benefits for extending the life of the tubing threads.

Operational challenge: J-groove of the clamp The high velocity flow of gas in the tubing can wear the J-groove inside the clamp. Solution: MLT fills the J-groove to make the inner part of the clamp smoother, reducing the abrasive effect of the gas and extending the life of the tubing. Operational Challenge: Casing In wells with complex downhole conditions, casing entry operations often rely on rotations and other operations to overcome frictional resistance. The rotation of the casing requires the cooperation of the top drive, CRT and tubing, and the ability of the casing to withstand a large enough torque is the key to the success of the operation. Solution: MLT can improve the tapered shape of the tubing male buckle (which is easily damaged during operation) to a certain extent, and provide protection to the tubing while increasing the rotational torque level of the knotted hoop.

Operational challenge: Casing threads Casing threads are often misbonded during casing butt joints, which reduces the working strength and sealing performance of the casing.

API Petroleum Casing Stubs Product Description

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Petroleum casing is a large diameter tubing that serves to secure the wall or borehole of oil and gas wells. The casing is inserted into the borehole and secured with cement to prevent the borehole from separating the rock formation and collapsing, and to ensure the circulation of drilling mud to facilitate drilling and extraction.
Steel grade of oil casing: H40, J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Casing end processing forms: short round thread, long round thread, partial trapezoidal thread, special buckle, etc. It is mainly used for oil well drilling to support the well wall during the drilling process and after the completion of the well to ensure the normal operation of the entire well after the completion of the well.
The important position of oil pipe
The petroleum industry is an industry that uses a large amount of petroleum tubing, and petroleum tubing plays an important role in the petroleum industry.
1 Oil tubing use is large, spend a lot of money, saving money and reducing the cost potential is huge. The consumption of oil well pipe can be projected by the annual drilling footage. According to the specific situation in China, roughly 62kg of oil tubing is needed for every 1m drilled, including 48kg of casing, 10kg of tubing. 3kg of drill pipe and 0.5kg of drill collar.
2 The mechanical and environmental behavior of oil tubing has an important impact on the adoption of advanced processes and increased production and efficiency in the oil industry.
3 Petroleum pipe failure loss is huge, starting from safety and reliability and oil life is of great importance to the oil industry.

Basic introduction and performance analysis of p110 petroleum casing

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p110 oil casing as oil casing is an important equipment for oil drilling, to our industrial construction and other practical activities to bring many positive impact and role, so what in-depth understanding of its en, small editors small popularization for you.

The basic introduction and performance analysis of p110 oil casing

I. Introduction

(1) The main importing countries of petroleum casing are: Germany, Japan, Romania, Czech Republic, Italy, Britain, Austria, Switzerland, the United States, Argentina, Singapore are also imported. Import

The standard mostly refers to the American Petroleum Institute standard API5A, 5AX, 5AC. steel grade is H-40, J-55, N-80, P-110, C-75, C-95, etc.. The specifications are mainly 139.77.72R-2, 177.89.19R-2, 244.58.94R-2, 244.510.03R-2, 244.511.05R-2, etc.

(2) There are three kinds of lengths specified by API: namely R-1 for 4.88 to 7.62m, R-2 for 7.62 to 10.36m, and R-3 for 10.36m to longer.

(3) Some of the imported goods are marked with the word LTC, i.e. long silk buckle casing.

(4) Imported casing from Japan in addition to the use of API standards, there are a small number of implementation of Japanese factory standards (such as Nippon Steel, Sumitomo, Kawasaki, etc.), steel grades are NC-55E, NC-80E, NC-L80, NC-80HE, etc.

(5) In the claim cases, there have been black buckle, wire buckle damage, tube body folding, broken buckle and thread tightness distance is over poor, joint J value is over poor and other appearance defects and casing brittle crack, low yield strength and other intrinsic quality problems.

II. Types

According to SY/T6194-96 “petroleum casing” is divided into two kinds of short threaded casing and its coupling and long threaded casing and its coupling.

Specification and appearance quality

(1) Domestic casing according to SY/T6194-96, the length of the casing is variable, the range of 8-13 m. But not shorter than 6 m of casing can be provided, the number of not more than 20%.

(2) The internal and external surfaces of the casing shall not have folding, hairline, delamination, cracks, rolling folds and scars. These defects shall be completely removed and the removal depth shall not exceed 12.5% of the nominal wall thickness.

(3) The outer surface of the joint shall not have defects such as folding, hairline, delamination, cracking, rolling, folding and scarring.

(4) The surface of casing and coupling threads shall be smooth, and no burrs, tears and other defects sufficient to interrupt the threads to affect the strength and tight connection are allowed.

III. Chemical composition inspection

(1)According to SY/T6194-96. The same steel grade is used for the casing and its coupling. Sulfur content of 0.045%, phosphorus content of 0.045%.

(2) according to the provisions of GB222-84 to take chemical analysis samples. Chemical analysis in accordance with the provisions of the relevant part of GB223.

(3) American Petroleum Institute ARISPEC5CT1988 1st edition regulations. Chemical analysis according to the new version of ASTME59 sample preparation, chemical analysis according to the new version of ASTME350.

Fourth, physical properties test

(1) According to SY/T6194-96. Do flattening test (GB246-97) tensile test (GB228-87) and hydrostatic test.

(2) According to the American Petroleum Institute APISPEC5CT 1988, 1st edition, hydrostatic test, flattening test, sulfide stress corrosion cracking test, hardness test (ASTME18 or E10 new version of the provisions of the test), tensile test, transverse impact test (ASTMA370, ASTME23 and the relevant standard new version of the provisions of the test), grain size determination (ASTME112 new version or other methods).

About p110 petroleum casing related content has been carefully sorted out for you, in fact, there are many related content, I will not introduce here one by one, we should grasp oh.

What kind of materials are petroleum casing made of?

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There are many different materials of oil casing, basic carbon steel, J55, L80, P110 and other special materials such as 3 cr, 9 cr, 13 cr, 22 cr, etc., mainly carbon dioxide resistant and known as hydrogen sulfide resistant materials such as 90 SS, 95 ss, etc. In addition, higher grade and nichrome alloy pipes are used depending on the manufacturer. Depending on the manufacturer, different numbers and special needs are also used, for example, material extrusion resistance, some manufacturers will increase TT to indicate extrusion resistance.

Oil casing is a steel pipe used to support the wall of an oil and gas well to ensure proper operation of the entire well after completion.
Depending on the drilling depth and geological conditions, several layers of casing should be used in each well. Cementing is used to cement the well after casing is placed. It is different from tubing and drill pipe and cannot be reused. It is a one-time consumption material.
Therefore, the consumption of casing accounts for more than 70% of all oil well pipelines.
According to the usage, oil casing can be divided into:conduit casing, surface casing, technical casing and reservoir casing.

API oil casing

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The use of steel pipe to manufacture ring-shaped parts can improve the material utilization rate, simplify the manufacturing process, save materials and processing hours, such as rolling bearing collars, jackets, etc., and has been widely used to manufacture steel pipe.

(1) The main importing countries of API oil casing are: Germany, Japan, Romania, Czech Republic, Italy, UK, Austria, Switzerland, USA, Argentina, Singapore are also imported.
(2) There are three kinds of lengths stipulated by API: namely, R-1 for 4.88 to 7.62m, R-2 for 7.62 to 10.36m, and R-3 for 10.36m to longer.　(3) Some of the imported goods are marked with the word LTC, i.e. long silk buckle casing.
(4) Imported casing from Japan, in addition to the use of API standards, there are a small number of implementation of Japanese factory standards.
(5) In the claim cases, there have been black buckle, fillet buckle damage, tube body folding, broken buckle and thread tightness distance exceeds the poor, joint J value exceeds the poor and other appearance defects and casing brittle crack, yield strength low and other inherent quality problems.

ASTM steel pipe can be divided into different steel grades according to the strength of the steel itself, i.e. J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Well conditions and depths are different, and the steel grade used is also different. In corrosive environments, the casing itself is required to have anti-corrosive properties, and API seamless steel pipe is required to have anti-crushing properties in places with complex geological conditions. Pumping pipe is mainly used to transport oil and gas from the bottom of oil wells to the surface.

API oil casing is mainly used for drilling of oil and gas wells and transmission of oil and gas. It includes oil drilling pipe, oil casing and pumping pipe.
Oil drill pipe is mainly used to connect drill collar and drill bit and transmit drilling power. Oil casing is mainly used to support the well wall during the drilling process and after completion to ensure the drilling process and the normal operation of the whole well after completion.

Oil casing is the lifeline to keep the well running. Due to different geological conditions, the downhole stress state is complex, and the combined effects of tensile, compressive, bending and torsional stresses on the tubing body place high demands on the quality of the casing itself. Once the casing itself is damaged for some reason, it may lead to production reduction or even scrapping of the whole well.

Oil casing pipe uses in oil and gas wells

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Oil casing is a steel pipe used to support the well wall of oil and gas wells to ensure that the drilling process is carried out and that the entire well operates properly after completion. Several layers of casing are used in each well depending on the drilling depth and geological conditions. The casing is cemented after the well is drilled, and unlike tubing and drill pipe, it is not reusable and is a one-time consumable material. Therefore, the consumption of casing accounts for more than 70% of all oil well tubing.

Oil special pipe is mainly used for drilling of oil and gas wells and transmission of oil and gas. It includes oil drilling pipe, oil casing and oil pumping pipe. Oil drill pipe is mainly used to connect drill collar and drill bit and transmit drilling power. Oil casing is mainly used to support the well wall during the drilling process and after completion to ensure the drilling process and the normal operation of the whole well after completion. The pumping tubing is mainly used to transport oil and gas from the bottom of the well to the surface.
Oil casing is the lifeline that keeps the well running. Due to the different geological conditions, the downhole stress state is complex, with tensile, compressive, bending and torsional stresses acting on the tubing body in an integrated manner, which places high demands on the quality of the casing itself. Once the casing itself is damaged for some reason, it may lead to production reduction of the whole well or even scrapping.
According to the strength of the steel itself, the casing can be divided into different steel grades, i.e. J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Different well conditions and depths require different steel grades. In corrosive environments, the casing itself is required to have corrosion resistance. In places with complex geological conditions, the casing is also required to have anti-crushing properties.

27MnCrV is a new steel grade for the production of TP110T steel grade casing. 29CrMo44 and 26CrMo4 are the conventional steel grades for the production of TP110T steel grade casing. 27MnCrV contains less Mo elements than the latter two, which can greatly reduce the production cost. However, the normal austenitizing quenching process is used to produce 27MnCrV with significant high-temperature temper brittleness, resulting in low and unstable impact toughness.
To solve such problems are usually used in two ways: one is the use of tempering after rapid cooling method to avoid high-temperature brittleness, to obtain toughness. The second is the sub-temperature quenching method through the incomplete austenitization of steel to effectively improve the harmful elements and impurities, improve toughness. The first method, relatively strict requirements for heat treatment equipment, requires the addition of additional costs.
AC1=736°C and AC3=810°C for 27MnCrV steel, the heating temperature during sub-temperature quenching is selected between 740-810°C. Sub-temperature quenching selected heating temperature 780 ℃, quenching heating holding time of 15min; quenching and tempering selected temperature 630 ℃, tempering heating holding time of 50min. due to sub-temperature quenching in the α + γ two-phase zone heating, quenching in the retention of part of the undissolved ferrite state, while maintaining a higher strength, toughness is improved.
At the same time, low-temperature quenching is lower than the conventional temperature, reducing the stress of quenching, thus reducing the deformation of quenching, which ensures the smooth operation of the production of heat treatment, and provides a good raw material for the subsequent wire turning process.
The process has been applied in the processing plant, quality assurance data show that the yield strength Rt0.6 in 820-860MPa, tensile strength Rm in 910-940MPa, impact toughness Akv in 65-85J between the steel pipe after heat treatment, 100% of the destruction resistance qualified. The data show that 27MnCrV steel pipe has been quite high quality high steel grade petroleum casing, on the other hand, also shows that the sub-temperature quenching process is a way to avoid high temperature brittleness in the production of steel products.

  1. Petroleum casing is a large diameter tubing that serves to hold the wall or well bore of oil and gas wells in place. The casing is inserted into the borehole and secured with cement to help isolate the borehole from rock formations and prevent collapse of the borehole, as well as to ensure the circulation of drilling mud for drilling and extraction.
  2. Steel grade of oil casing: H40, J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Casing end processing forms: short round thread, long round thread, partial trapezoidal thread, special buckle, etc. It is mainly used for oil well drilling to support the well wall during the drilling process and after the completion of the well to ensure the normal operation of the entire well after the completion of the well.
  3. The important position of oil pipe
  4. The petroleum industry is an industry that uses a large amount of petroleum tubing, and petroleum tubing occupies a very important position in the petroleum industry.
  5. 1, oil tubing usage, spending a lot of money, saving money, cost reduction potential is huge. The consumption of oil well pipe can be projected by the annual drilling footage. According to the specific situation in China, roughly 62kg of oil tubing is needed for every 1m of drilling, including 48kg of casing, 10kg of tubing. 3kg of drill pipe and 0.5kg of drill collar.
  6. the mechanical and environmental behavior of oil tubing has an important impact on the adoption of advanced technology and increased production and efficiency in the oil industry.
  7. The failure loss of oil pipe is huge, and its safety, reliability and service life are of great importance to the oil industry.

How are the steel insolation joints welded?

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Insulation joints are mainly used in the sealing protection of oil and gas pipelines and to prevent electrochemical corrosion. They are mainly composed of short joints, steel flanges, fixing rings, seals, insulation plates, insulation sleeves and filling insulation materials. Seals can be O-ring seal, U-ring seal and “O-shaped + U-shaped” composite seal, although the sealing structure is different, but they have the same sealing principle. Its sealing principle is: the sealing ring under the action of the external preload to produce elastic deformation and the sealing force required to ensure that the medium in the pipeline is not leakage. The following is an example of X80 DN1200 PN120 insulated joint to illustrate its welding process.

The material of the insulating joint in this experiment is API 5L X80, and the size is 1 219mm×27.5mm. The main body pressure forging steel (flange, fixed ring) material is F65, Ⅳ class; The sealing part is fluorine rubber U-shaped sealing ring, which has the characteristics of reliable sealing, low water absorption, high compressive strength, good elasticity and electrical insulation. Insulation plate material has strong electrical insulation performance, resistance to fluid penetration and low water absorption. Forged flange in accordance with ASTM A694 for F65 C, Mn, P, S content and carbon equivalent, crack resistance index, hardness and impact energy requirements. After testing, the metallographic structure is pearlite + ferrite, uniform structure, no segregation, the average grain size is 8 grade. The finer grain size ensures the high strength and toughness of the forgings.

Welding procedure qualification

For the welding of this product, after stress removal treatment, tensile, bending, impact, hardness, metallography and spectral analysis tests, the results meet the specifications.

1. Welding groove

  • According to the material properties and wall thickness of pipe fittings and flanges, choose the appropriate groove form and size, namely double V groove
  • When designing the size and type of welding groove, the influence of welding heat input on the performance of sealing elements is considered, and the lower heat input is adopted for welding to ensure that the rubber sealing ring close to the weld will not be burned out in the welding process. narrow gap groove is determined according to our years of experience in welding all-welded ball valve.

2. Welding method

The “argon arc welding backing + submerged arc welding filling and covering” of welding method. According to the selection principle of welding materials for high alloy steels with different steel grades stipulated in the pressure vessel welding code and standard, the welding materials matching with the grade of F65 steel were selected, which could not only ensure the strength requirements of F65 and X80 material, but also have good toughness.

Flange-nipple welding

Flanges and pipe joints are welded by argon arc welding and automatic submerged arc welding. Argon arc welding for backing welding, and then automatic submerged arc welding for filling and covering welding.

1. Welding equipment.

Subsubmerged arc automatic welding machine: speed 0.04 ~ 2r/min, workpiece clamping range Φ330 ~ Φ2 700mm, the maximum length of the weldable workpiece 4 500mm, the maximum welding seam depth 110mm, can bear the weight of 30t.

Submerged arc welding has the advantages of reliable weld quality, beautiful weld bead forming, high deposition rate, and can be widely used in large diameter insulation joints, all-welded buried ball valves, etc.

(2) Welding method.

GTAW+SAW welding method. Firstly we use argon arc welding root backing and filling each time to ensure the root melt through, and then use submerged arc automatic multi-layer multi-pass welding method to complete filling and covering.

Post weld heat treatment

In order to reduce the residual stress of the weld and prevent the weld from cracking or stress deformation, it is necessary to de-stress and tempering after welding. SCD type rope electric heater (18.5m long) and LWK-3×220-A type temperature control box are used for heat treatment. K-type armored thermocouple is selected as temperature measuring equipment. The heat treatment temperature was 550℃, and the heat preservation time was 2hour.

The material of the insulating joint in this experiment is API 5L X80, and the size is 1 219mm×27.5mm. The main body pressure forging steel (flange, fixed ring) material is F65, Ⅳ class; The sealing part is fluorine rubber U-shaped sealing ring, which has the characteristics of reliable sealing, low water absorption, high compressive strength, good elasticity and electrical insulation. Insulation plate material has strong electrical insulation performance, resistance to fluid penetration and low water absorption. Forged flange in accordance with ASTM A694 for F65 C, Mn, P, S content and carbon equivalent, crack resistance index, hardness and impact energy requirements. After testing, the metallographic structure is pearlite + ferrite, uniform structure, no segregation, the average grain size is 8 grade. The finer grain size ensures the high strength and toughness of the forgings.

Welding procedure qualification

For the welding of this product, after stress removal treatment, tensile, bending, impact, hardness, metallography and spectral analysis tests, the results meet the specifications.

1. Welding groove

  • According to the material properties and wall thickness of pipe fittings and flanges, choose the appropriate groove form and size, namely double V groove
  • When designing the size and type of welding groove, the influence of welding heat input on the performance of sealing elements is considered, and the lower heat input is adopted for welding to ensure that the rubber sealing ring close to the weld will not be burned out in the welding process. narrow gap groove is determined according to our years of experience in welding all-welded ball valve.

2. Welding method

The “argon arc welding backing + submerged arc welding filling and covering” of welding method. According to the selection principle of welding materials for high alloy steels with different steel grades stipulated in the pressure vessel welding code and standard, the welding materials matching with the grade of F65 steel were selected, which could not only ensure the strength requirements of F65 and X80 material, but also have good toughness.

Flange-nipple welding

Flanges and pipe joints are welded by argon arc welding and automatic submerged arc welding. Argon arc welding for backing welding, and then automatic submerged arc welding for filling and covering welding.

1. Welding equipment.

Subsubmerged arc automatic welding machine: speed 0.04 ~ 2r/min, workpiece clamping range Φ330 ~ Φ2 700mm, the maximum length of the weldable workpiece 4 500mm, the maximum welding seam depth 110mm, can bear the weight of 30t.

Submerged arc welding has the advantages of reliable weld quality, beautiful weld bead forming, high deposition rate, and can be widely used in large diameter insulation joints, all-welded buried ball valves, etc.

(2) Welding method.

GTAW+SAW welding method. Firstly we use argon arc welding root backing and filling each time to ensure the root melt through, and then use submerged arc automatic multi-layer multi-pass welding method to complete filling and covering.

Post weld heat treatment

In order to reduce the residual stress of the weld and prevent the weld from cracking or stress deformation, it is necessary to de-stress and tempering after welding. SCD type rope electric heater (18.5m long) and LWK-3×220-A type temperature control box are used for heat treatment. K-type armored thermocouple is selected as temperature measuring equipment. The heat treatment temperature was 550℃, and the heat preservation time was 2h.

Anticorrosion coating treatment of structural steel plate

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Generally speaking, the surface treatment of structural steel plates is needed to increase their anti-corrosion and durability. The quality of surface treatment directly affects the adhesion of the coating to the substrate of the coated workpiece and the corrosion resistance of the material. Oil, grease, dust and other contaminants will cause the paint film to fall off or produce a variety of appearance defects, anticorrosive coating can improve the anticorrosive protection of the paint layer on the steel plate and the smooth surface of the base steel. Common anticorrosive coatings require a substrate surface cleanliness of SA2.5 or above, and steel plate surface coatings provide excellent corrosion protection for the water treatment industry, pulp and paper mills, Bridges and offshore facilities.

According to the design and drawings, the anti-corrosion coating on the exposed part of the bridge support and the shock-absorbing steel plate is treated to prolong its service life. The main construction method is epoxy zinc-rich primer construction, according to the requirements of the design position of the steel plate to achieve protection purposes. The process includes base surface cleaning → primer coating (epoxy zinc-rich primer 50μm, 2 times) → finish coating (modified polyurethane topcoat 50μm, 2 times) → inspection and acceptance. The supporting plan of coating is as follows:

ItemsCoat paintingColorPaint film thicknessTheoretical paint (g/m2)Coating interval(20℃)
Surface treatmentThe surface should be strictly derusting with a quality standard Sa2.5
First layer （2times）Epoxy zinc rich primer-conventional 50% zincGrey80-100μm40-50μm/time1～7days
Second layer （2times）Anticorrosive topcoat-modified polyurethane topcoatGreen80-100μm40-50μm/time1～7days  

The base surface cleaning

Before the paint is brushed, the coating and rust of the exposed part of the steel plate of the support and the shock absorber plate are polished off with an Angle grinder. The quality standard for rust removal is SA2.5.

Primer coating (epoxy zinc-rich primer 50μm, 2 coats)

1) Epoxy zinc-rich primer, according to the ratio of 9∶1 and control the viscosity of the paint, the system should be fully stirred, so that the paint color and viscosity is uniform, curing 25 ~ 30 minutes, the paint needs to be used up within 4 ~ 6 hours.

2) Brush the first layer of primer brushing direction should be consistent, neat. Apply multiple times to prevent the brush from running too much paint.

3) Maintaining a certain time after the first brush, to prevent paint not dry paint flow drop. Brush the second time after the first drying. The direction should be perpendicular to the first time and the film thickness should be uniform.

Finish coating(modified polyurethane finish 50μm, 2 times)

1) Top paint is green. The finish coat should be made of a modified polyurethane finish of the same color, in accordance with the appropriate proportion. Full mixing before use and uniform color to ensure that the coating does not fall, do not show grain.

2) The method and direction should be the same as the above process.

3) The coating interval between top coat and primer should be more than 2 days.