Advantages of lined stainless steel composite pipe:
1. No scaling, no nodulation, corrosion resistance
The thin-walled stainless steel pipe is compounded in the steel pipe. The material of the stainless steel pipe is 0Cr18Ni9 (the American standard is AISI304) specified in "GB12771-2000 Stainless Steel Welded Steel Pipe for Fluid Transportation". Since the steel contains 18% chromium, the inner wall of the pipe is in use. A very thin chromium oxide film is formed, which prevents the metal from continuing to oxidize, so stainless steel has strong corrosion resistance, not only can withstand the corrosion of water and air, but also can withstand the corrosion of weak acid and weak alkali. The thickness of the inner stainless steel pipe is 0.4-1.2 mm, while the thickness of the galvanized layer of the galvanized steel pipe is only 0.07 mm, the thickness difference is 5.7-17 times. The corrosion resistance and compactness of the stainless steel are stronger than the galvanized layer of the galvanized steel pipe. . Therefore, there is no need to worry about scaling and nodules caused by the corrosion of the inner wall during use, and the inner hole will be reduced.
The outer steel pipe in the lined stainless steel composite steel pipe is a welded steel pipe produced according to "GB/T3091-2001 Welded Steel Pipe for Low-Pressure Fluid Transport", or a seamless steel pipe produced according to "GB/T8163-1999 Seamless Steel Pipe for Fluid Transport". Steel pipes, or spiral seam welded pipes produced according to "Spiral seam submerged arc welded steel pipes produced by SY/T5037-2000". The outer layer steel pipe lined with stainless steel composite steel pipe for oil and natural gas transportation is produced according to GB/T9711-1997 "Technical delivery conditions for steel pipe for oil and natural gas industry". The tensile strength of welded steel pipes or seamless steel pipes is not less than 335MPa, and the elongation rate is not less than 15%. The elongation rate of the outer steel pipe of the lined stainless steel composite steel pipe for conveying natural gas and oil reaches 25%. The hydraulic pressure test, and through the standard specified bending test or flattening test. The gas and oil transmission pipes produced according to GB9711 shall also undergo fracture toughness test, metallographic examination, tensile test and high-strength pressure test. The total wall thickness and strength are increased after the stainless steel pipe is compounded in the outer steel pipe, which can be used not only for civil water and gas transmission, but also for industrial fluid transportation. When the outer layer steel pipe adopts welded steel pipe, since the welding seam of the outer layer steel pipe and the stainless steel pipe is not in the same position, the strength reliability of the composite steel pipe is improved.
3. Can be welded
3.1 Welding can be used between lined stainless steel composite steel pipes. The welding process can refer to GB/T13148-1991 "Technical Conditions for Welding Stainless Steel Clad Steel Plates". Also refer to Appendix A of JB/T4790-2000 "Welding Regulations for Steel Pressure Vessels". "Welding Specification for Stainless Steel Clad Steel".
3.2 The groove form can use the butt joint No. 6 of GB/T13148 Figure 1, which can also be seen in Figure 1 of this article.
3.3 Before welding, mechanical methods and organic solvents should be used to remove oil, rust, metal chips, oxide films and other contaminants on the surface of the weld and at least 20mm on both sides of the welding groove.
3.4 The welding rod adopts the A302 (E309) welding rod specified in GB/T983 "stainless steel welding rod", and the specification is Φ3.2. 3.5 Welding method
Manual arc welding is recommended; argon tungsten arc welding can be used for bottoming of welds with higher requirements, manual arc welding is used for parts close to carbon steel, or argon tungsten arc welding is used for all. When argon tungsten arc welding is used, the welding wire adopts A302 welding wire with the same composition as E309.
3.6 Welding equipment
The welding equipment should meet the welding process requirements and comply with the relevant equipment standards. DC welding machine is recommended when using manual arc welding.
3.7 Welding procedure
First weld the clad material (stainless steel pipe), then weld the transition layer, and finally weld the base material (carbon steel pipe).
3.8 Welding Requirements
The surface of the cladding weld should be kept as smooth and smooth as possible with the surface of the cladding. When welding the transition layer, on the premise of ensuring good fusion, the amount of fusion of the base metal should be reduced as much as possible, that is, the fusion ratio should be reduced. For this purpose, a smaller diameter electrode or wire should be used, and a smaller welding wire energy should be used. The excess height of the butt weld shall not be greater than 1.5mm.
3.9 Cleaning up after welding
After welding, the welding slag, weld spatter and other contaminants on the surface of the weldment should be carefully cleaned. Welds should be trimmed locally if necessary. After the cleaning is completed after welding, the welder's mark should be marked on the obvious parts near the weld of the base material for future inspection.
3.10 Qualification of welding procedures
When the product technical conditions require welding procedure qualification, the welding procedure qualification must be carried out before the start of construction, see "JB4708-2000 Steel Pressure Vessel Welding Procedure Qualification" for details.
The welding seam of our company's stainless steel composite steel pipe has passed the "Welding Procedure Evaluation Report" made by the Ship Technology Research Institute of China Shipbuilding Industry Corporation: the tensile strength of the welded sample of the composite steel pipe reaches 550-565N/mm2.
3.11 The welded pipe fittings made of steel butt welded seamless pipe fittings shall comply with GB/T12459-1990, the welded pipe fittings made of steel plate butt welded pipe fittings shall comply with GB/T13401-1992, and the welded pipe fittings used for transporting oil and gas shall comply with SY/T0510- 1998 "Steel Butt Welding Fittings" and SY/T5257-2004 "Steel Bends".
4 can be flanged
Fig. 2 is a flange in which the pipe body (1) and the flange (4) are welded. As shown in Fig. 2, the pipe body (1) is a lined stainless steel composite steel pipe. Flange holes (42) are arranged in the flange (4), and bolts (43) and nuts (44) are installed in the holes. The pipe body (1) is placed in the inner hole (45) of the flange body (4) as shown in Figure 2, and the pipe body (1) and the flange (4) are welded by electric welding to form a weld (46). The welding rod is made of stainless steel, so that after the two flanges (4) and (48) are tightened by bolts (43) and nuts (44), the contact surfaces (47) of the two flanges (4) and (48) are tightly When the fluid flows in the pipe, the fluid only contacts the stainless steel layer (13) and the stainless steel weld (46) in the pipe body (1) lined with stainless steel composite steel pipe to ensure the purity of the fluid.
5 can be screwed
The connection between the DN15-DN100 water delivery steel pipe and the pipe fittings adopts the pipe thread specified in "GB7306 Pipe Thread Sealed by Thread". The pipe thread connection surface is a thread with crossed teeth. The tolerance generated during machining will disappear during the thread tightening process. , when the lever arm of the wrench is 200 mm long, the pipe thread is screwed once, the palm moves 628 mm, the pipe body advances a pitch of 2.309 mm, a difference of 272 times, the tightening force of the pipe body is 272 times the rotational force, a huge tightening Ensure that there is no leakage after tightening between the pipe body and the pipe fittings. The contact surface of the pipe threaded connection is steel and stainless steel, and the expansion coefficient is very close during thermal expansion and contraction.
Stainless steel threaded pipe fittings are cast by austenitic stainless steel specified in GB2100. The grade is ZG07Cr19Ni9. They are precision castings with smooth surface and precise dimensions. The structure of stainless steel threaded pipe fittings is shown in Figure 3. There is a step in contact with the tube end of the tube body, and a silicone sealing ring is placed on the step. In order to prevent the silicone sealing ring from falling into the tube, there is a stainless steel retaining ring in the silicone sealing ring. When the thread between the pipe fitting and the pipe fitting is tightened, the end of the pipe body is in contact with the silicone rubber sealing ring, which cuts off the contact between the outer steel pipe, the end face of the pipe body and the internal fluid, ensuring that the pipeline system can transport pure water. In this way, only stainless steel pipes and stainless steel pipe fittings are in contact with the fluid, which ensures the corrosion resistance of the entire pipeline system. The joint seal of the lined stainless steel composite steel pipe is a double-layer seal, the outer layer is a pipe thread seal, and the inner layer is a special-structured silicone rubber sealing ring, which ensures the reliability of the sealing of the pipeline system. The HA alloy coating can also be plated on the shouldered malleable casting pipe, and its corrosion resistance can reach the corrosion resistance of stainless steel. "Alloy-coated HA steel pipe and pipe fittings" urban construction industry standard is being submitted for approval.
6. Can be grooved
Due to the large diameter of DN125-DN600 pipe fittings, it is difficult to process threads and tighten threads, so DN125-DN600 pipe fittings should use grooved pipe joints and plastic-lined flanges. The grooved pipe joint is the implementation of the urban construction industry standard "CJ/T156 grooved pipe joint". The outer surface and end face of the grooved pipe joint are treated by electrostatic spraying, and the ductile iron grooved pipe joint can also be plated with HA alloy coating, and the corrosion resistance level of the coating reaches the corrosion resistance level of stainless steel. The sealing ring of silicone rubber or food-grade nitrile rubber is wrapped in the joint, and the fluid flowing in the pipe will not contact the outer steel pipe.
A groove is extruded on the outer surface of the end of the lined stainless steel composite steel pipe, and the two ends of the grooved pipe joint are pressed into the groove. The grooved pipe joint is composed of two-lobed grooved pipe joints. The grooved pipe joints of the petals are connected by bolts and nuts. When the bolt and nut are tightened, the two grooved pipe joints are tightly fastened together, and the silicone rubber sealing ring in the grooved pipe joint is pressed tightly. Holding together, the fluid flows in the tube and the sealing ring, ensuring the tightness of the fluid flow, see Figure 5 for details.
In order to solve the corrosion problem of the pipe end face, we design the end face anti-corrosion sleeve. The outer surface of the anti-corrosion sleeve and the inner surface of the lined stainless steel composite steel pipe form an interference fit, so that the end-face anti-corrosion sleeve is close to the pipe end face of the lined stainless steel composite steel pipe, and sealant is applied between the end-face anti-corrosion sleeve and the end face and inner surface of the steel pipe. , The sealant is a two-component, and when the two-component is mixed together, a great adhesive force is produced immediately. The end-face anti-corrosion sleeve and sealant can solve the anti-corrosion problem of the pipe end face when the grooved connection is used, as shown in Figure 5.
7. High temperature resistance, can transport hot water, boiling water, steam
The connecting pipe fittings lined with stainless steel composite steel pipes are made of HA alloy-plated malleable iron pipe fittings produced according to "GB3287-1982 Malleable Iron Pipe Connection Fittings" or pipe fittings precision cast with 304 stainless steel. The HA alloy-plated malleable iron pipe fittings and 304 stainless steel precision casting pipe fittings can withstand temperatures above 250°C, and can transport hot water, boiling water and steam.
304 stainless steel is heat-resistant steel, and its tensile strength at 400°C still reaches 412Mpa, which is higher than that of ordinary steel at room temperature. Therefore, the high temperature resistance of the lined stainless steel composite steel pipe is very good, and it can be used to transport hot water, boiling water and steam.
8. Good low temperature brittleness and small expansion coefficient
The degree of thermal expansion and contraction of plastic is 10 times higher than that of steel, and the elongation capacity of plastic is much lower than that of steel when it is cold and shrinked. Therefore, when the water in the pipe freezes and expands in cold seasons, the plastic pipe cannot shrink and recover after freezing and expanding. The secondary expansion accumulates, causing the plastic to expand beyond the limit and cause brittle fracture. The welded steel pipe ensures the elongation rate exceeds 15%, and the elongation rate of the 304 stainless steel pipe is guaranteed to exceed 25%. The outer layer steel pipe that can stretch and expand, and the stainless steel pipe with better inner lining elongation rate can avoid brittleness when the water in the pipe freezes and expands. break. According to the regulations of GB/T9711, the lined stainless steel clad steel pipe for conveying natural gas and oil should be subjected to -40 ℃ Charpy impact.
9. Resistant to weak acid corrosion
3 The corrosion rate of 04 stainless steel in 10% nitric acid at 20°C is less than 0.1 mm per year, the corrosion rate in 10% boiling acetic acid is less than 0.1 mm per year, and the corrosion rate in 50% citric acid at 20°C is less than 0.1 mm per year. Less than 0.1 mm per year in 20% potassium hydroxide at 20°C, less than 0.1 mm per year in 80% phosphoric acid at 60°C, and less than 0.1 mm per year in 2% sulfuric acid at 50°C The corrosion rate is 0.016 mm per year. It adopts lined stainless steel composite steel pipe with stainless steel welded pipe fittings and stainless steel flanges, which can be used to transport weakly acidic or weakly alkaline chemical fluids.
10. The inner wall is smooth and the fluid flow resistance is small
The lined stainless steel pipe in the lined stainless steel composite steel pipe is welded by cold-rolled stainless steel strip. The surface of the cold-rolled stainless steel strip is smooth and clean, so the inner wall of the stainless steel pipe is smooth, the fluid resistance in the pipe is small, no scaling, and no fluid pollution.
11. Good hygienic performance, can transport clean water
Since the stainless steel pipe is not corroded by the fluid during use, and the stainless steel pipe body has no impurities entering the fluid, after testing, its various hygienic indicators are better than the "GB/T17219 Safety Evaluation Standard for Drinking Water Transmission and Distribution Equipment and Protective Materials" ”, the content of various metal elements such as iron, manganese, copper, zinc, cadmium, lead, silver, chloroform, carbon tetrachloride, benzo, etc. detected in high-sensitivity testing equipment is far below the specified value, obtaining sanitary License approval. Because the lined stainless steel composite steel pipe is equipped with stainless steel threaded pipe fittings, stainless steel flanges, and stainless steel welded pipe fittings, the fluid does not contact the outer steel pipe, and the fluid only contacts the stainless steel. Therefore, the lined stainless steel composite steel pipe can replace the pure stainless steel pipe to transport drinking water.
12. Reliable anti-corrosion coating
The outer anti-corrosion layer can be made into a hot-dip galvanized layer according to the regulations of "GB/T3091 Welded Steel Pipe for Low-Pressure Fluid Transport", and the thickness of the galvanized layer is 0.072 mm. It can also be made into polyethylene anti-corrosion layer according to "SY/T4013-1995 Technical Standard for Polyethylene Anti-corrosion Layer of Buried Steel Pipeline", and the thickness of the anti-corrosion layer can reach 0.5-2.5 mm.
13. Inexpensive
The lined stainless steel composite steel pipe is covered with a thin-walled stainless steel pipe, which reduces the manufacturing cost and ensures the thickness to ensure the strength, so that the installation cost of the lined stainless steel composite steel pipe is much lower than that of the thick-walled pure stainless steel pipe and the thick-walled stainless steel pipe. Pure copper tube.
Craftsmanship:
In the production of stainless steel composite pipes, the composite steel pipe manufacturers must be required to select different corrosion-resistant alloy layers as lining pipes according to the requirements of the technical process of salt chemical enterprises. In terms of domestic technology level, most corrosion-resistant alloys (such as pure titanium, nickel-based alloys, and ordinary stainless steel) can be used as inner linings. But for duplex stainless steel (such as: LC2242), it is very difficult to compound. The reason is that the yield strength of duplex steel is relatively large and the elongation at break is small. If the process control is not precise enough, it is very easy to crack during the composite process. It is understood that there are few manufacturers in the world that can produce composite lined with duplex stainless steel. Steel Pipe. Due to the existence of two metallographic structures, austenite and ferrite, duplex stainless steel is much better than 316L in terms of resistance to chloride ion corrosion and stress corrosion cracking, and the price is comparable to 316L. In salt production or salt chemical enterprises, the use of duplex stainless steel composite steel pipes has great performance advantages.
