What special requirements should be paid attention to when cutting CrMo steel alloy steel pipes?
Plasma cutting or laser cutting is recommended for CrMo steel pipe cutting. If flame cutting is used, it must be preheated to 200-250℃. The cutting speed should be 20% lower than that of carbon steel to avoid hardening of the cut. It is recommended to use segmented cutting for steel pipes with a thickness of more than 50mm. All cutting surfaces must be polished to remove the heat-affected zone, and magnetic particle detection should be performed to check for microcracks. Carbide saw blades should be used for cold cutting in precision machining occasions to keep the feed speed stable. Material identification should be done after cutting to prevent confusion with other steel materials.
What are the best practices for bending CrMo steel alloy steel pipes?
Cold bending is suitable for CrMo steel pipes with a wall thickness of <12mm. The bending radius should not be less than 3 times the pipe diameter, and a mandrel should be used to prevent wrinkles. The heating temperature during hot bending is controlled at 900-950℃ to avoid grain coarsening caused by exceeding 1000℃. It is recommended to use an induction heating pipe bending machine for large-diameter thick-walled pipes to ensure temperature uniformity. Normalizing treatment (890-910℃) must be performed after bending to eliminate residual stress. Bends in key parts need to be tested by UT and hardness to ensure that there are no structural defects.
What are the key steps in the preparation work before welding CrMo steel alloy steel pipes?
Before welding, 100% PT testing is required to confirm that the groove is defect-free, the machining groove angle is 60°±5°, and the blunt edge is 1-2mm. The preheating temperature is determined according to the wall thickness: <12mm requires 150-200℃, 12-25mm requires 200-250℃, and >25mm requires 250-300℃. The welding rod must be dried at 350℃×1h and stored in a 110℃ insulation cylinder. Use a copper clamp when assembling, and the misalignment is controlled within 10% of the wall thickness. Oil and moisture must be thoroughly removed within 50mm of the welding area.
How to scientifically determine the support spacing during the installation of CrMo steel alloy steel pipes?
The support spacing calculation needs to comprehensively consider the specific gravity of the medium, the working temperature and the pipe specifications, and usually refers to the ASME B31.1 standard. Taking the DN200 15CrMo steam pipe (400℃) as an example, the standard support spacing is 4.5m, which is 15% shorter than the carbon steel pipe. High-temperature pipelines must be equipped with spring supports to absorb thermal expansion, and the sliding supports must use stainless steel friction pairs. A guide bracket should be set every 6m for vertical pipelines to limit lateral displacement. Vibrating pipelines need to add dampers, and the support spacing is reduced by another 20%.
What are the special requirements for inspection and maintenance of CrMo steel alloy steel pipes after installation?
The pressure test requires clean water with a chloride ion content of <25ppm and a test pressure of 1.5 times the design pressure. 100% RT inspection of welds + 20% UT spot check, and 100% MT inspection of fillet welds. The system needs to be hot-tightened before commissioning, and the bolts need to be tightened again at the operating temperature. Daily maintenance includes checking the status of supports and hangers every quarter, measuring the creep deformation of high-temperature pipe sections every year, and conducting a comprehensive wall thickness test every three years. If local thinning exceeds 10%, residual strength assessment must be carried out.
