Medium: NaOH solution; questions regarding material selection
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This post was last edited by yechao25038 on 2019-3-3 at 14:26. Operating pressure: 2.7 MPa; design pressure: 3.0 MPa; design temperature: 300°C; concentration of NaOH solution: 20%. I checked the \"Corrosion Data and Material Selection Manual\" but could not find any corrosion data related to these operating conditions. 1. The cylinder body is made of N6+Q345R composite steel plates; the nozzles are made of N6 material, the flanges are integral flanges lined with N6, and S31603 is chosen for the mating flanges. Is this material selection appropriate? What material is good for the stirring shaft and paddles? 2. Does this equipment require heat treatment in accordance with HG/T20581—7.8.1? 3. Since it is an N6 composite plate, should the corrosion margin still be taken as 3 mm in accordance with item 2 of 7.8.1?
High-temperature heat and alkali – I don’t think using composite panels is a good idea; I’ve never seen it done before
What material is generally chosen for such operating conditions?
This post was last edited by wanlirn on 2019-3-3 at 16:13. Conditions of 3.0 MPa and 300 degrees are a bit too severe for a single-layer N7 material (in reality it’s N6; the new standard for nickel plates, “NBT 47046-2015 Nickel and Nickel Alloy Plates for Pressure Equipment”, uses N7 in place of N6. It doesn’t matter if the names keep changing – it’s all the same thing). A corrosion allowance of 0.5 mm should be sufficient; however, the diameter isn’t known, and cost is an issue. Additionally, the composite panel itself poses no major issues in terms of standard blasting; it’s the joints that represent a test of your company’s manufacturing control capabilities. . . . Have you done work with composite nickel or titanium plates? Be cautious when taking on this kind of work
Why is it not suitable? Are composite panels not appropriate for high temperatures?
1. The maximum operating temperature for N6 material is 300 degrees; it is preferable to use nickel-based alloys. The cylinder heads should be made of composite plates, the pipe flanges can adopt a welded ring flange structure, the stirring shaft can be constructed with a low-alloy tube covered by a nickel-based alloy tube, and the impeller itself should be made of nickel alloy. 2. According to the JB/T4756 standard, this equipment does not require heat treatment. 3. Corrosion margin 3 applies to carbon steel and low-alloy steel materials.
This post was last edited by yechao25038 on 2019-3-4 09:38 :handshake:handshake Thank you!
The final material selection decision made by the company’s management: cylinder N6+Q345R； The equipment is equipped with manholes, facilitating the replacement of the stirrers; therefore, both the stirrers and the stirring shafts are made of 316L, while the fastening screws used to hold the stirrers are made of Monel 400 ； The U-bolts used for fixing the coil are made of N6 material, while the nuts are made of 316L.