Rectangular Stainless Steel Hollow Tubes
The tensile strength of stainless steel is important for applications where the conductor is subjected to mechanical stress, and that's why stainless steel hollow conductors are used for manufacturing the stator winding bar of turbogenerator, and the winding bars consists the rectangular stainless steel hollow tubes as well as insulated solid copper conductor. In the turbogenerator, a very high current flows through the insulated solid copper conductor generates big amount of heat, meanwhile cold water flows through these rectangular stainless steel hollow conductors and absorb the heat generated by the insulated solid copper conductors. Therefore, premium quality of these rectangular stainless steel tubes is vital for successfully running of the generator and minimizing damage during fault conditions. To achieve this quality, the rectangular stainless steel tubes need to go through stringent tests relating to corrosion chemical properties, mechanical test, eddy current test, wrinkle-re-deflection test, leak-proofness test.
What are the quality requirements for stainless steel hollow conductor?
To deliver satisfactory quality, Fabmann needs to carry out the following tests:
√ Chemical analysis
√ Wrinkle and re-deflection (bending and re-bending) test for conductors drawn from welded tube
√ Corrosion test, and the resistance to inter-crystalline corrosion is verified as per EN lS0 3651-2
√ On-line eddy current test
√ Leak test with air under water (6 bar for a duration of minimum 30 second)
√ Mechanical test
√ Outer and inner surface quality inspection
What are the popular grades for stainless steel hollow conductors?
The choice of material for stainless steel hollow conductors depends on a balance of factors, including the desired electrical conductivity, mechanical properties, corrosion resistance, cost, and application requirements. Austenitic stainless steels such as 304 and 316, offer excellent corrosion resistance and good formability, making them suitable for water cooled windings of turbogenerator, and following grades are the popular options:
√ 304 stainless steel, the most widely used grade for hollow conductors due to its good corrosion resistance, formability, and moderate electrical conductivity.
√ 316L stainless steel, it offers improved corrosion resistance compared to 304, making it suitable for applications in harsh environments.
√ 430 stainless steel, it has higher strength and lower cost than 304 and 316L, but its corrosion resistance is lower.
√ Duplex stainless steel, it offers a combination of high strength and corrosion resistance.
√ S321 (00Cr18Ni10Ti), contains approximately 18% chromium, 8% nickel, and 0.3% titanium, and the addition of titanium stabilizes the microstructure of the steel meanwhile makes the metal
material more resistant to intergranular corrosion and high temperature.
Eddy Current Test of Rectangular Stainless Steel Tubes
What is the production process for the stainless steel hollow conductor?
Fabmann has very solid production experience of rectangular stainless steel tubes such as material grade X2CrNi19-11 (material number 1.4306) which is an austenitic stainless steel, and we supply the seamless type as per EN 10216-5 with solution annealed. Among the sophisticated production processes, annealing with sufficiently rapid cooling down is critical, and the annealing temperature should be in range of 1000℃, duration of 3 - 5 minutes. This Austenitic stainless steel hollow conductor is chosen for better mechanical property as well as better resistance to intergranular corrosion, and that's why focusing on chemical composition analysis is always the first step when it comes to production process control. This stainless steel hollow conductor tubing requires rather complicated production processes below:
√ Stainless steel rod preparation including chemical analysis before next production process starts.
√ Piercing, concentricity shall always be controlled properly.
√ Mother tubing acceptance check
√ Milling surface of the mother tubing
√ Few rounds of cold drawing
√ Heat treatment
√ Polishing
√ Straightening
√ Eddy current test
√ Cutting
√ Leak test
√ Drying
√ Final visual inspection
√ Packing
The above mentioned production process also reflects that many process controls shall be in place to verify each production process is according to our control plan, and below is the what our quality team does for verifying quality for each delivery. The following control points are always very covered:
√ Chemical composition in % by mass
√ Wrinkle and re-deflection, bending and re-bending test
√ Corrosion chemical test, inter-crystalline corrosion as per EN lSO 3651-2.
√ Leak test as per EN lSO 10893-1
√ Eddy current test as per EN ISO 10893-2.
√ Mechanical properties as per EN lSO 6892-1
1 Grain Size Check
2 Inter-crystalline Corrosion Test
3 Dimension Check by Projection
4 Online Dimension Check
5 Matercial Thickness Check
6 Straightening Process
7 Straightness and Twist Check
8 Eddy Current Test Online
9 Mechanical Test
10 Leak Test
11 Visual Inspection
12 Final Inspection
During the whole production processes, many inspections are conducted before next process starts. Full attention has not been only paid to dimension but also mechanical property & surface quality. Fabmann has implemented a very strict production control plan to make sure all of our delivery can meet your expectation.
Our Custom Fabrication Service
Fabmann provides custom fabrication service for different rectangular stainless steel tubes with different thickness, and the normal thickness range is between 0.5mm upto 1.5mm, section area ranging from 50mm² upto 200mm² with tubing length upto 12 meters or more. Our standard production leadtime is between 60 days to 75 days depending upon volume, and we provide comprehensive inspection report before delivery.
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