Lined stainless steel composite pipe is a bimetallic pipe constructed from a carbon steel base pipe and laminated with a stainless steel lining through processes such as diameter reduction, cold expansion, deflagration, or brazing. It complies with standards such as CJ/T192-2004 and CJ/T192-2017. The outer layer is made of hot-dip galvanized steel pipe, seamless steel pipe, or spiral welded pipe, while the inner layer is austenitic stainless steel such as 304 or 316L. Available sizes range from DN15 to DN1800. This product is suitable for cold water, hot water, fire water supply, and petrochemical, pharmaceutical, food, and natural gas transportation. It has been used in key projects such as the G20 Hangzhou International Expo Center and the Three Gorges Project.

This pipe combines the corrosion resistance of stainless steel with the high strength of carbon steel. Mechanical diameter reduction and hydrostatic cladding ensure a bond strength of ≥0.2 MPa. Connection methods include welding, threading, flanges, and grooved connections. Welding must be performed using A302 (E309) electrodes in layers, with a minimum excess height of 1.5 mm. Inspections include hydraulic testing, flattening testing, and eddy current testing. The outer layer's anti-corrosion treatment meets Sa2.5 rust removal standards, and the inner layer's sanitary properties meet GB/T17219 requirements. The company is equipped with bimetallic tube eddy current flaw detectors and other equipment, with an annual production capacity of 200,000 tons. The company is ISO9001 certified for its quality management system.

Advantages

1. No scaling, no nodules, and corrosion resistance.

The thin-walled stainless steel pipe is composited within the steel pipe. The stainless steel pipe is made of 0Cr18Ni9 (AISI304 in the US standard), as specified in "GB12771-2000 Stainless Steel Welded Steel Pipes for Fluid Transportation." Because the steel contains 18% chromium, a very thin chromium oxide film forms on the inner wall of the pipe during use. This film prevents further oxidation, resulting in stainless steel's strong corrosion resistance. It withstands corrosion from water and air, as well as weak acids and bases. The thickness of stainless steel-lined composite pipes ranges from 0.4 to 1.2 mm, while the zinc coating on galvanized steel pipes is only 0.07 mm, a thickness difference of 5.7 to 17 times. Stainless steel also offers superior corrosion resistance and density compared to the zinc coating on galvanized steel pipes. Therefore, during use, there's no need to worry about scaling or nodules forming on the inner wall due to rust, which could reduce the bore size.

The outer steel pipe of stainless steel-lined composite pipes is welded steel pipe produced in accordance with GB/T3091-2001, Welded Steel Pipes for Low-Pressure Fluid Transportation; seamless steel pipe produced in accordance with GB/T8163-1999, Seamless Steel Pipes for Fluid Transportation; or spirally welded pipe produced in accordance with SY/T5037-2000, Spiral Submerged Arc Welded Steel Pipes. The outer steel pipe of stainless steel-lined composite pipes used for oil and natural gas transportation is produced in accordance with GB/T9711-1997, Technical Delivery Conditions for Steel Pipes for the Petroleum and Natural Gas Industry. The tensile strength of welded or seamless steel pipes must be no less than 335 MPa, and the elongation must be no less than 15%. The outer steel pipe of stainless steel-lined composite steel pipes for natural gas and oil transportation must have an elongation of 25%. All pipes must undergo a water pressure test exceeding 3.0 MPa and pass the required bending or flattening tests. Gas and oil pipelines produced in accordance with GB9711 must also undergo fracture toughness testing, metallographic examination, tensile testing, and high-intensity pressure resistance testing. The addition of stainless steel pipe to the outer steel pipe increases the overall wall thickness and strength, making it suitable not only for civil water and gas transportation but also for transporting industrial fluids. When welded outer steel pipes are used, the weld seams of the outer and stainless steel pipes are not located in the same location, improving the strength and reliability of the composite pipe.

3. Weldability

3.1 Welding is permitted between stainless steel-lined composite steel pipes. For welding procedures, refer to GB/T13148-1991, "Technical Requirements for Welding of Stainless Steel Composite Plates." Refer also to Appendix A of JB/T4790-2000 "Welding Code for Steel Pressure Vessels." Also refer to "Welding Code for Stainless Steel and Clad Steel."

3.2 The groove type may be butt-weld type 6 in GB/T13148.

3.3 Before welding, mechanical methods and organic solvents should be used to remove oil, rust, metal shavings, oxide film, and other contaminants from the weld surface and within a radius of at least 20 mm on both sides of the weld groove.

3.4 The welding rod should be A302 (E309) with a diameter of 3.2 mm as specified in GB/T983 "Stainless Steel Welding Rods."

3.5 Welding Method
Manual arc welding is recommended. For welds with higher requirements, argon tungsten arc welding can be used for the base, manual arc welding can be used for areas close to carbon steel, or argon tungsten arc welding can be used throughout. When using argon tungsten arc welding, use A302 wire with the same composition as E309.

3.6 Welding Equipment
Welding equipment must meet welding process requirements and comply with relevant equipment standards. A DC welder is recommended for manual arc welding.

3.7 Welding Procedure
First, weld the composite material (stainless steel pipe), then the transition layer, and finally the base material (carbon steel pipe).

3.8 Welding Requirements
The composite material weld surface should be as smooth and flat as possible with the composite material surface. When welding the transition layer, minimize the amount of base metal incorporated while ensuring good fusion, thereby reducing the fusion ratio. To this end, use smaller diameter electrodes or wires and lower wire energy. The butt weld reinforcement should not exceed 1.5 mm.

3.9 Post-weld Cleaning
After welding, carefully clean the weld surface of the weldment from weld slag, weld spatter, and other contaminants. Localized weld trimming should be performed as necessary. After post-weld cleaning, a welder's mark should be placed in a conspicuous area near the base material weld for future inspection.

3.10 Welding Procedure Qualification
When product specifications require a welding procedure qualification, it must be conducted before construction begins. For details, see "JB4708-2000 Welding Procedure Qualification for Steel Pressure Vessels."
The "Welding Procedure Qualification Report" for the welds of our company's stainless steel-lined composite steel pipes, prepared by the Shipbuilding Process Research Institute of China State Shipbuilding Corporation, indicates that the tensile strength of the composite steel pipe weld specimens reached 550-565 N/mm².

3.11 Welded pipe fittings made of seamless steel butt-weld fittings must comply with GB/T12459-1990. Welded pipe fittings made of steel plate butt-weld fittings must comply with GB/T13401-1992. Welded pipe fittings used for transporting oil and natural gas must comply with SY/T0510-1998 "Steel Pipe Butt-Weld Fittings" and SY/T5257-2004 "Steel Bends."

4 Flange connection possible

The pipe body (1) and the flange (4) are welded flanges, and the pipe body (1) is lined with a stainless steel composite steel pipe. The flange (4) has a flange hole (42), and bolts (43) and nuts (44) are installed in the hole. The pipe body (1) is placed in the inner hole (45) of the flange body (4), and the pipe body (1) and the flange (4) are welded by electric welding to form a weld (46). The welding rod is a stainless steel welding rod. After the two flanges (4) and (48) are tightened by the bolts (43) and nuts (44), the contact surfaces (47) of the two flanges (4) and (48) are tightly attached together. 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 the stainless steel composite steel pipe, ensuring the purity of the fluid.

5. Threaded Connections

DN15-DN100 water supply steel pipes and fittings are connected using pipe threads specified in "GB7306 Pipe Threads for Threaded Sealing." The threaded connection surfaces are cross-threaded. The tolerances introduced during machining disappear during the tightening process. With a wrench arm length of 200 mm, for every turn of the pipe thread, the hand moves 628 mm, while the pipe advances one thread pitch of 2.309 mm, a difference of 272 times. The tightening force on the pipe is 272 times the rotational force. This enormous tightening force ensures leak-free connection between the pipe and fitting. The contact surfaces of the pipe threaded connection are steel and stainless steel, and their coefficients of expansion are very similar during thermal expansion and contraction. Stainless steel threaded pipe fittings are cast from austenitic stainless steel specified in GB2100, with the designation ZG07Cr19Ni9. They are precision castings with smooth surfaces and precise dimensions. They feature a shouldered design, with a step between the shoulder and the pipe end. A silicone seal rests on the step, and a stainless steel retaining ring is placed inside the silicone seal to prevent it from falling into the pipe. When the threads are tightened, the pipe end contacts the silicone rubber seal, isolating the outer steel pipe and pipe end from the internal fluid, ensuring the pipeline system can transport pure water. This ensures that only the stainless steel pipe and fittings come into contact with the fluid, ensuring corrosion resistance throughout the entire pipeline system. The joint seal for stainless steel-lined composite pipes is a dual-layer seal: an outer seal for the pipe threads and an inner seal for a specially constructed silicone rubber seal, ensuring a reliable seal for the pipeline system. Shouldered malleable pipe fittings can also be coated with an HA alloy coating, achieving corrosion resistance comparable to that of stainless steel. The "Alloy-Coated HA Steel Pipe and Fittings" urban construction industry standard is currently under approval.

6. Grooved Connections Available

Due to the larger diameters of DN125-DN600 pipe fittings, threading and tightening are more difficult. Therefore, grooved pipe fittings with plastic-lined flanges should be used for these fittings. Grooved pipe fittings comply with the urban construction industry standard "CJ/T156 Grooved Pipe Fittings." Grooved pipe fittings are electrostatically sprayed on the exterior and end faces. Ductile iron grooved pipe fittings can also be coated with an HA alloy coating, achieving corrosion resistance comparable to that of stainless steel. Silicone rubber or food-grade nitrile rubber seals are enclosed within the fittings, ensuring fluid flow does not come into contact with the outer steel pipe. Grooves are extruded into the outer surface of the stainless steel composite lined steel pipe end, into which the ends of the grooved pipe fitting are pressed. The grooved pipe fitting consists of two halves, connected by bolts and nuts. When the bolts and nuts are tightened, the two halves snap together, compressing the silicone rubber sealing ring inside the grooved pipe fitting. The silicone rubber sealing ring holds the two pipe ends together, allowing fluid to flow through the pipe and the sealing ring, ensuring a tight seal.
To address corrosion issues on pipe ends, we have designed an end-face corrosion sleeve. The outer surface of the sleeve forms an interference fit with the inner surface of the stainless steel composite lined steel pipe, ensuring a tight fit between the sleeve and the pipe end. A two-component sealant is applied between the sleeve and the pipe end and inner surface. When used, the two components are mixed together to create a strong bond. End-face anti-corrosion sleeves and sealant effectively address corrosion issues with grooved connections.

7. High-temperature resistance, capable of conveying hot water, boiling water, and steam

The stainless steel-lined composite pipe connectors utilize HA alloy-plated malleable iron fittings manufactured in accordance with "GB3287-1982 Malleable Cast Iron Pipe Connectors" or 304 stainless steel precision-cast fittings. HA alloy-plated malleable iron fittings and 304 stainless steel precision-cast fittings can withstand temperatures exceeding 250°C and can convey hot water, boiling water, and steam.

304 stainless steel is a heat-resistant steel with a tensile strength of 412 MPa at 400°C, exceeding the tensile strength of ordinary steel at room temperature. Therefore, stainless steel-lined composite pipes offer excellent high-temperature resistance and can be used to convey hot water, boiling water, and steam.

8. Good low-temperature brittleness and low expansion coefficient.

Plastics expand and contract with heat more than 10 times that of steel, yet their ability to stretch when exposed to cold is much lower than that of steel. Therefore, when water freezes and expands inside the pipe during cold weather, the plastic pipe cannot recover after the freezing. This repeated expansion accumulates, causing the plastic to expand beyond its limit and fracture. Welded steel pipes should ensure an elongation of more than 15%, and 304 stainless steel pipes should ensure an elongation of more than 25%. The outer steel pipe should be able to expand and contract, and the inner lining should have a stainless steel pipe with a higher elongation to prevent brittle fracture when the water freezes and expands inside the pipe. According to GB/T9711, stainless steel-lined composite pipes used to transport natural gas and oil must be subjected to a -40°C Charpy impact test.

9. Weak Acid Corrosion Resistance

The corrosion rate of 304 stainless steel in 10% nitric acid at 20°C is less than 0.1 mm per year, in 10% boiling acetic acid less than 0.1 mm per year, in 50% citric acid at 20°C 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 less than 0.1 mm per year, and in 2% sulfuric acid at 50°C less than 0.016 mm per year. Lined stainless steel composite pipes, equipped with stainless steel welded fittings and flanges, can be used to transport weakly acidic or alkaline chemical fluids.

10. Smooth Inner Wall, Low Fluid Flow Resistance

The inner stainless steel pipe in the lined stainless steel composite pipe is welded from cold-rolled stainless steel strip. The cold-rolled stainless steel strip has a smooth surface, resulting in a smooth inner wall, low fluid resistance, and no scaling or contamination. 11. Excellent Hygienic Performance, Suitable for Transporting Purified Water

Since stainless steel pipes are not corroded by fluids during use, and no impurities enter the pipe body, testing has shown that all hygienic indicators exceed those specified in "GB/T17219 Safety Evaluation Standard for Drinking Water Transmission and Distribution Equipment and Protective Materials." The levels of various metal elements, such as iron, manganese, copper, zinc, cadmium, lead, silver, chloroform, carbon tetrachloride, and benzophenone, detected by highly sensitive testing equipment, are far below the specified values, resulting in the approval of a hygienic license. Because stainless steel-lined composite pipes are equipped with stainless steel threaded fittings, stainless steel flanges, and stainless steel welded fittings, the fluid does not come into contact with the outer steel pipe, only with the stainless steel. Therefore, stainless steel-lined composite pipes can replace pure stainless steel pipes for transporting purified drinking water.

12. Reliable Corrosion Protection of the Coating

The outer coating can be hot-dip galvanized in accordance with the requirements of "GB/T3091 Welded Steel Pipes for Low-Pressure Fluid Transportation," with a galvanizing thickness of 0.072 mm. Polyethylene anticorrosion coatings can also be applied according to the "SY/T4013-1995 Technical Standard for Polyethylene Anticorrosion Coatings for Buried Steel Pipes," with a thickness of 0.5-2.5 mm.

13. Low Price

Stainless steel-lined composite pipes are constructed by cladding a thin-walled stainless steel pipe within a steel pipe. This reduces manufacturing costs while ensuring sufficient thickness for strength, making the installation cost of stainless steel-lined composite pipes significantly lower than that of thick-walled pure stainless steel and copper pipes.

Manufacturing Process

The production of stainless steel composite pipes requires the composite pipe manufacturer to select different corrosion-resistant alloys for the lining layer based on the process requirements of the salt chemical industry. Based on domestic process technology, most corrosion-resistant alloys (such as pure titanium, nickel-based alloys, and ordinary stainless steel) can be used as linings. However, duplex stainless steels (such as LC2242) are more challenging to clad. The reason is that duplex steel has a relatively high yield strength and low elongation at break. If process control is not precise, it is very likely to crack during the cladding process. It is understood that few manufacturers worldwide can produce composite steel pipes lined with duplex stainless steel. Due to its internal microstructures of austenite and ferrite, duplex stainless steel significantly outperforms 316L in terms of resistance to chloride ion corrosion and stress corrosion cracking, while being priced similarly to 316L. In salt production and salt chemical industries, the use of duplex stainless steel composite pipes offers significant performance advantages.