Material selection for equipment foundation bolts

Q355 is a type of steel material. It is a low-alloy steel (C0.45%); preheating is required before welding, with a preheating temperature of T0=100–150°C, and an interpass temperature of Ti≤400°C. 6. Post-weld heat treatment parameters: To reduce welding residual stresses, lower the hydrogen content in the weld, and improve the metal structure and properties of the weld, heat treatment should be applied to the weld after welding. The heat treatment temperature is 600–640°C; the holding time is 2 hours (for a plate thickness of 40 mm), and the rate of temperature change is 125°C/h. IV. On-site welding sequence: 1. Preheating before welding – Before welding the flange plates, they are first preheated; welding begins after maintaining this temperature for 30 minutes. The preheating, interpass temperature, and heat treatment during welding are automatically controlled by a heat treatment temperature control cabinet. Far-infrared crawler-type heating elements are used, with a microcomputer responsible for automatically setting and recording the temperature curves, while thermocouples are used to measure the temperature. During preheating, the measuring point of the thermocouple is 15 mm–20 mm away from the edge of the groove. 2. Welding 2.1 To prevent welding deformation, each column joint is welded symmetrically by two people, with the welding direction proceeding from the center toward the sides. When welding the inner face (the groove that is close to the web), small-scale welding procedures must be used for the first to third layers, as welding in these areas is the main cause of welding deformation. After welding layers 1 to 3 is completed, root cleaning is performed on the back side. After completing root cleaning using carbon arc gas gouging, the weld must be mechanically ground to remove any carburized material from its surface and to reveal a metallic luster, thereby preventing cracks caused by excessive carbonization in the surface layer. The outer edge should be welded in one go, with the remaining part of the inner edge being welded last. 2.2 When welding the second layer, the welding direction should be opposite to that of the first layer, and so on. The welding joints in each layer should be offset by 15-20 mm. 2.3 The welding current, welding speed, and number of welding passes for the two welders should be kept consistent during welding. 2.4 During welding, the process should start at the starting plate and end at the ending plate. After welding, cut it off and polish it clean. 3. Post-weld heat treatment: Heat treatment should be carried out within 12 hours after the welding of the joint is completed. If heat treatment cannot be carried out promptly, insulation and slow cooling measures should be taken. During heat treatment, two thermocouples should be used for temperature measurement, with the thermocouple tips welded to the inner and outer sides of the weld joint. The welding temperature curve for Q355 steel is shown in Figure 4 below. Welding inspection: In accordance with the requirements of the \"Code for Construction and Acceptance of Steel Structure Projects\", the welds are inspected using ultrasonic testing, with an inspection rate of 100%. V. On-site Technical Management 1. Prepare detailed welding operation instructions. 2. Full-process control of the welding process is key to ensuring quality. When welding each column joint, a dedicated person should monitor the welding process; if the welder fails to follow the operating instructions, welding must be stopped immediately. During the welding process, the heat treatment technician should monitor the interlayer temperature throughout the entire process; if it exceeds the specified limit, they must immediately inform the welder to pause work. 3. Enhancing the quality awareness of construction workers is key to implementing welding procedures. Before construction begins, a briefing is conducted for all staff, and welding procedure cards are provided. The briefing explains in detail the characteristics of the welding process, as well as the necessity of strictly controlling the on-site welding process and the key points for such control. VI. Conclusion: By following these welding process measures, a total of 102 welds were constructed on site, and the first-time pass rate for non-destructive testing reached 100%. Verified through actual construction, this welding process measure not only enables on-site guidance for welding Q355 steel but also ensures welding quality. Note: All Q355 mentioned in the text corresponds to Q345 under the old standard; they are actually the same, please be aware of this.

Q355C is what used to be called Q345C; it is a commonly used material in steel structures. Is it difficult to purchase? ? ? ?

According to the national standard \"Low-alloy high-strength structural steel\" GB/T 1591-2018, as of February 1, 2019, the steel grade Q345 was discontinued and replaced by Q355, which corresponds to the EU standard steel grade S355. Q355 is a common low-alloy high-strength steel with a yield strength of 355 MPa. GB/T 1591-2018 Low-alloy high-strength structural steel Q355B/ Q355C/ Q355D/ Q355E Q355D-Z15/Z25 Q355E-Z25/Z35

It has been learned; it needs to be carried out according to the design. It cannot be changed to a lower-grade material. The foundation bolts of structures like towers are all calculated to ensure they have sufficient strength.

This post was last edited by bluishice on 2019-9-27 at 17:13. In Northeast Liaoning, shouldn’t low-temperature embrittlement be taken into consideration? Generally, C indicates use up to 0°C, D indicates use up to -20°C, E indicates use up to -40°C; or the meanings may vary depending on the standard.

On the 3rd floor are the materials I found; they are designed for use in the low-temperature conditions of winter in the northeast. I believe that at least the Q355D grade is necessary – the Q355C grade is a bit too low. The main difference among various Q355 grades lies in their phosphorus content. In general, the phosphorus content in steel should be kept below 0.045%. This is because phosphorus dissolves completely in iron, and it forms iron phosphate together with ferrite, especially at low temperatures. When the phosphorus content reaches 0.045%, a critical condition is reached, leading to cold brittleness in the steel. Another harmful element is sulfur; sulfur does not dissolve in iron but exists in the form of ferrous sulfide. Ferrous sulfide, along with iron, forms low-melting-point eutectics, which cause thermal brittleness in steel at high temperatures. Generally, the sulfur content in steel is kept below 0.05%.