What welding materials should be used for welding 15CrMo steel pipe?
For manual welding rods, choose E5515-B2 (R307), for submerged arc welding, use H13CrMoA welding wire + SJ101 flux, and for argon arc welding, choose TIG-R30. The composition of the welding material must match the parent material (Cr-Mo system), and the diffusible hydrogen content must be ≤5mL/100g. Before welding, the flux is dried at 350℃ for 1 hour, and the welding rod is kept warm at 150℃.
How to control welding preheating and interlayer temperature?
Preheating temperature 250℃~300℃ (wall thickness>10mm), interlayer temperature 200℃~350℃. The temperature measuring point is within 75mm from the weld, and an infrared thermometer is used for monitoring. Insufficient temperature is prone to cold cracks, and excessively high temperature will cause grain coarsening. When the ambient temperature is <5℃, a heat preservation shed must be set up.
What are the key parameters of post-weld heat treatment (PWHT)?
PWHT temperature is 620℃~650℃, heating rate is ≤220℃/h, cooling rate is ≤260℃/h. Insulation time is calculated according to wall thickness: 1.5min/mm (minimum 2 hours). The treatment effect of tank furnace is better than local heating, ensuring temperature uniformity within ±15℃.
How to detect the quality of 15CrMo welds?
100% radiographic flaw detection (RT) complies with NB/T 47013.2 Level II standard, or ultrasonic flaw detection (UT) Level B acceptance. Hardness test requires weld ≤240HB, heat affected zone (HAZ) ≤270HB. Face bending/back bending test is also required (bending core diameter 4T, angle 180° without cracks).
Common welding defects and preventive measures?
Cold cracks: strict preheating, use low-hydrogen welding materials.
Reheating cracks: control the PWHT heating rate to avoid retention in the 600℃ sensitive range.
Lack of fusion: Optimize the groove angle (60°±5°) and increase the welding current by 10%~15%.
