Due to the poor weldability and cold-cracking susceptibility, there is high risk of cold cracking during the welding of ASTM A335 P11 seamless pipes. Several special measures shall be taken during the welding process and relative inspection shall be conducted after the welding process finished.

Special Measures During Welding

1. Before the welding of ASTM A335 P11 pipes, the welding electrodes shall be carefully preheated at the temperature of 300~350°C for 1 hour and the preservation temperature is 80~120°C. Thermal shock or quenching shall be avoided during preheating to prevent the electrode-coating from cracking. The rust or oil stain shall be cleaned before welding.
2. Gas Arc Welding(GAW) shall be adopted as the tack welding method and its positioning weld-seam shall be ground. The length of tack-welding seam is 10~20 mm while its height is 2~4 mm with the quantity no less than 4 distributing uniformly along the circumference. Preheating shall be conducted before tack welding.
3. During the welding of A335 P11 pipes, the environment must be considered and controlled. When the natural wind flows too fast, the welding joints may be hardened and hydrogen content may be increased. Thus, the two ends of the pipe shall be covered to prevent the wind from flowing through. The humidity rate shall be less than 90%. When SMAW or GTAW is applied, the flow rate of natural wind shall be controlled relatively to less than 8 m/s or 2 m/s.
4. The interpass temperature shall be sustained at the temperature no less than preheating temperature. Since PWHT may not be immediately done after welding, a post-weld heating shall be conducted: keep 300~350°C for 30 minutes and gradually cool it down to room temperature.
5. The the preheating of PWHT shall be conducted in accordance with the following points: heating temperature[600~675°C], heating rate[95 °C/h], preservation time[2.5 hours], cooling rate[110 °C/h], heating-width[L≥600 mm]. After post-weld heat treatment, the hardness of welding seam and heat-affected zones shall be no greater than 225 HB.

Inspection and Tests for Welding Joints of ASTM A335 P11 Pipes

During the welding of ASTM A335 pipes, X-Ray inspection shall be implemented when the welding seam is thicker than 15 mm. The 100% ultrasonic test(UT) and 10% magnetic particles test(MT) shall be done 24 hours after the welding finished. Tiny oscillation welding and multiple-interpasses & multiple-seams shall be implemented. If suspension occurs during the welding process, dye-penetration inspection shall be conducted before it restarts. When welding-repair is required, the hardened surface of welding seam shall be ground and removed carefully. No further welding action is permitted until dye-penetration inspection approves it.