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Study on the production process of pipeline anticorrosion
Jan 30, 2019

In order to give full play to the advantages of technology, raw materials, geography, cost and policy, and make it have strong market competitiveness, a large domestic steel pipe production enterprise plans to build an internal coating and an external anticorrosion production line.The construction of anticorrosive production line will improve the scale, technology and equipment level and product level of the enterprise as a whole, and maintain the sustainable development of the enterprise.Through a lot of investigation and field work of relevant technical personnel, the construction scheme of anticorrosive production line in the steel pipe plant is put forward.The author introduces the construction scheme, process arrangement and main production equipment.


  1. Construction scale and product plan



    1.1 construction scale

At present, most of the domestic foreign minister's pipeline steel pipes need to be anticorrosion, the external anticorrosion is mainly oil and gas pipeline, and the inner coating is mainly natural gas pipeline.Based on the current situation of the enterprise and the market demand forecast in normal years, considering the construction investment comprehensively and avoiding excessive market competition and other factors, the program determines that the annual production capacity of internal coating and external anticorrosion is 150 X 104 square meters.


1.2 product plan


(1) internal coating product scheme.Pipe diameter.To 1422 mm, pipe length 8-12.5 m, maximum wall thickness 20.6 mm, type of internal coating for drag reduction type of two-component liquid epoxy, the implementation standard is API RP 512 and SY IT 6530-2002.


(2) external anti-corrosion product scheme.With a diameter of 377-1422 mm, pipe length of 8-12.5 m, maximum wall thickness of 20.6 mm, external corrosion type is single and double bonded epoxy powder, two and three layers of polyethylene/polypropylene.The executive standards are DIN330670, CSA z245.20-2002, CSA z245.21-2002, SY/ t0413-2002 and SY/T 0315-1997, respectively.


2 production process


2.1 types of corrosion protection


At present, the main external anticorrosive structure at home and abroad are: single and double bonded epoxy powder, two and three layers of polyethylene, three layers of polypropylene, petroleum asphalt and coal tar paint, etc..Steel pipeline according to the transmission medium and pressure, as well as the geographical location of the temperature, humidity, topography and landform, plus the population, culture, economy and other different conditions, can use different external anti-corrosion structure and materials, so as to achieve the safety and reliability of pipeline requirements.The inner coating can be divided into anticorrosion type and resistance type according to its function.The domestic anticorrosive internal coating with cement mortar and epoxy powder as the main coating material has been used for many years in different pipe diameters of water pipelines.At present, the inner coating drag reduction technology is widely used in the main natural gas pipelines at home and abroad to reduce the friction and improve the transportation.After years of application and development, coating production and construction technology of inner coating are becoming more and more mature.


2.2 external anti-corrosion production line


The process flow of the external anticorrosion production line is shown in figure 1.


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1) copper pipe preheating


Before derusting, the surface of the steel tube must be dry and oil-free. The temperature of the tube should be 5 degrees Celsius above the dew point temperature, or below the dew point temperatureTo preheat, preheat the temperature is 40-60 degrees Celsius.


(2) cast away nine rust


Steel pipe before derusting should remove the surface of grease, dirt, welding slag, burr, etc., and then blasting derusting.


(3) purge in copper tube


The compressed air nozzle is used to stretch into the pipe to blow away the rust residues and steel sand in the pipe to ensure that the coating does not fall into the spraying room.


(4) derusting detection


The steel pipe after derusting shall be tested in accordance with relevant regulations to meet the requirements of derusting grade.The qualified steel pipe is put into the outer coating, and the unqualified steel pipe is returned for rust removal.


(5) pipe end sticker


In order to facilitate on-site welding, a certain pre-reserved section is required at both ends of the pipe body, and the reserved section length is selected according to the design requirements, generally 100-150 mm.Apply the sticker or removable paint according to the reserved section width before applying.


(6) dust treatment


Before entering the coating chamber, the steel pipe is treated with micro-dust to remove some of the micro-dust on the surface of the steel pipe after derusting, so as to improve the adhesion of the coating.


(7) medium frequency heating


The tube body is rapidly and evenly heated to about 220 c by means of medium frequency induction heating with yuan pollution to meet the need of coating temperature.


(8) epoxy powder primer coating


Epoxy powder coatings with excellent anticorrosive and mechanical properties, such as good adhesion, anti-cathodic stripping, etc., are used as the primer for single layer epoxy powder, double layer epoxy powder and three-layer structural layer.The coating is applied to the heated steel tube by electrostatic spraying with a thickness of 60-100um and determined by the design.



(9) adhesive IPE extrusion side winding


For the three-layer structure coating, the middle layer is the adhesive, the outermost layer is the PE layer, the two kinds of coating, the adhesive plays the role of bonding primer and PE two different polar materials;For two layers of PE structure layer, the bottom layer is adhesive, the outermost layer is PE layer.The two coating materials are extruded into sheets and wound around the tube body by a plastic extruder and a special die head.



(10) coating surface rolling


Just finished coating the PE layer of steel pipe, through the pressure will be pressed into a single layer of multiple PE layer leaves, and the PE layer and other components are connected together, to ensure the coating of the formation and uniformity, but also to prevent air inclusion in the layer.


(11) incision


Because the pipe one after another for a continuous operation, and the tube body at both ends of the requirement of a certain reserved section, so before coating must according to the width of the reserved section stickers or coating brush removable paint, after coating with artificial cut off the continuous coating between the two sections, and peel off the reserved section coating.


(12) cooling


After coated steel tube, coating in the tube body is still in the melting state, can not be in contact with the work line transmission wheel, it needs to be rapidly cooled to about 60 degrees Celsius.


(13) end grinding


After removing the coating of the reserved section at both ends of the steel pipe, it shall be polished clean and the end surface of the coating shall be polished into groove, so that the coating can be combined with the coating better.


(14) coating quality inspection


Carry out quality inspection of pinhole, peeling, thickness and impact according to relevant regulations.


(15) identification


Label qualified finished pipe, including coating structure, pipe diameter, length, production unit and date.


2.3 internal coating production line


Process flow of inner coating production line

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(1) preheating


Before derusting, the inner surface of the steel tube must be dry and oil-free. The temperature of the tube body should be 5 degrees Celsius above the dew point temperature. If the temperature is lower than the dew point temperature, it shall be preheated with a preheating temperature of 40-50 degrees Celsius.


(2) cast nine rust


Before carrying out the internal blasting/peening treatment on the steel pipe, grease, dirt, welding slag and burr on the inner surface shall be removed, and then the process of blasting/peening shall be carried out.


(3) quality inspection after derusting


The steel pipe after derusting shall be tested in accordance with relevant regulations to meet the requirements of derusting grade.


(4) the incision


In order to facilitate on-site welding, a certain reserved section is required at both ends of the pipe body. The length of the reserved section is selected according to the design requirements, generally 50-80 mm.Apply the sticker or removable paint according to the reserved section width before applying.


(5) spraying


The inner surface and end of the steel tube shall be sprayed immediately after treatment.


(6) curing


After internal coating, the steel pipe is sent to the curing furnace for curing.


(7) quality inspection of inner coating


Test coating quality according to relevant regulations.



(8) identification


Mark qualified finished pipe. According to the calculation, it takes 34 h to complete 150 x 104m2 internal coating and external anti-corrosion coating, but the annual effective working time of the unit is 44: h, and the unit load rate is 3402144: =77.0%.Therefore, the unit can fulfill the capacity requirements.


3 Main production equipment


3.1 equipment selection


Through the actual investigation of a large number of engineering and technical personnel, and from the production scale, product quality, equipment investment, production cost and other aspects of comprehensive consideration, determine the anti-corrosion production line key production equipment including shot blasting and rust removal equipment, intermediate frequency heating device, extrusion machine, all mechanical equipment are domestic.


See performance parameters of main equipment of inner coating and outer anticorrosion production line


3.2 features of main production equipment


The blast chamber is welded with shaped steel frame and steel plate to ensure sufficient rigidity and strength of the chamber body. The wear-resisting high anchor steel lining plate is installed on the side of the blast chamber to improve the service life.Shot blasting machine adopts the upper structure, shot blasting machine is mainly composed of impeller, impeller driving disc, shot splitting wheel, directional disc, blade, motor, high anchor wear-resisting protective lining plate, damping rubber, etc.BE type full screen curtain flow screen automatic adjustment type pellet slag separator, elevator adopts flat belt drive bucket elevator, discharge mode is centrifugal gravity type, belt tensioning adjustment range is 200 mm.The dedusting equipment is composed of a primary cyclone dust collector and a secondary pulse backblowing bag dust remover.


3.2.2 if heating mounting straight


Using thyristor if device and thyristor element, the power frequency three-phase ac power supply is converted into single-phase if power supply.The frequency regulation system and the current and voltage regulation closed-loop system automatically track the change of load during the start-up process.The circuit adopts specially designed constant power control circuit, which can automatically monitor the change of voltage and current during operation and output power automatically according to the change of load.Adopting digital control circuit, high reliability, three-phase power phase sequence and capacitance ark and furnace attachment are not need to be specified, and the power supply heat processing capacity in the process of using larger heating electrical components for cooling, the device adopts the inner and outer binary system, using pure water or steam water as the main circulation cooling medium, using common as auxiliary circulation cooling water medium, different diameter steel pipe production should choose reasonable specifications of the sensor.Sensor coil by the high quality large cross-section torque type copper winding, winding insulation enamel coating moistureproof, in and out of the pipes by using quick joint connection, appearance is square sensor installed on the height adjustable bracket, can I use the infrared temperature measurement equipment monitoring of steel tube surface temperature, static accuracy + / - 2%, and through the signal recorder for connection for data collection, storage and processing.


3.2.3 FBE electrostatic coating system


The design of the corona type high voltage electrostatic automatic powder gun satisfies the application of spraying the hot melt epoxy powder on the outside of the pipe under the condition of high temperature.High voltage electrostatic generating system can generate up to 100 kV(DC) electrostatic voltage, to ensure the high speed and high film thickness pipe spray application to obtain a higher powder rate, meet the strict industrial equipment safety standards, safe operation.Module design structure is convenient for daily cleaning and maintenance, multiple gun system controller in 19 # control ark, Ann controller for powder spray gun corresponding to each pump for air flow and powder flow control, high voltage electrostatic charging output voltage can be adjusted within 0-100 kv, in order to improve the intensity of electric field, and get the best operating flexibility.The system is equipped with multiple protection such as material level alarm device, flame alarm device and carbon dioxide fire extinguishing system.The spray chamber adopts stainless steel structure and is equipped with lighting equipment.The powder recovery adopts the type of cyclone with filter element, and the filter element material adopts the composite material of polyester fiber + microporous aluminum cylinder. The product can eliminate the static electricity and wash the powder repeatedly.


3.2.4 PE/PP coating system



5J220 x 30 single screw extruder is used to extrude PE/PP material. The possible impurities in the material are filtered out through the net changer connected with the host machine to avoid damaging the die head. PE/PP sheets are extruded through the adapter and the connected t-shaped mold.Use 5J90x30 single-screw extruder to extrude adhesive material, filter impurities that may exist in the material through the net changer connected with the host machine to avoid damaging the die head, extrude adhesive sheet material through the adapter and the t-shaped mould connected with it.When the steel pipe spirals pass through the coating area, the plastic sheet is driven to wrap on the surface of the steel pipe. At the same time, the pressing material made of silica gel compacts the film onto the surface of the steel pipe to increase the peeling strength and exhaust the air that may be sandwiched between the film and the steel pipe.In order to prevent the pipe from being prone to bubbles due to the possible sinking of the pipe end when passing through the coated area, a custody trolley is set here.


4 conclusion


With the development of petroleum, chemical, natural gas and other industries in China, the scale of pipeline construction is becoming larger and larger.At the same time,Ji's attention is also from the pipeline anticorrosion.The scheme of pipeline anticorrosion production technology needs to be further explored to create greater social and economic benefits for the development ofPipeline industry.