In-Service Welding Concerns;
When welding, repairing or modifying pipelines or equipment that are currently being used (In-Service), the most worrying is the leak of the fluid inside. While or after doing On-line Welding. The two main reasons that cause the leak are:
- Burn Through: While welding at the melting area of the welding, the strength will be reduced. We may not be able to withstand the Pressure at Service value.
- Weld Cracking or Hydrogen Induced Cracking (HIC) from welding. The additional concern in welding is the cooling rate. Since the inside of the pipe or equipment has fluid flow, it may cause a fast weld-cooling rate. And that makes the structure become brittle.
Controlling the Heat Input in in-service welding to prevent Burn Through is very important. According to Standards (API / ASME), we recommend the use of welding wires with a small Diameter (3/32 in, 2.4 mm) for First Weld Pass, especially for workpieces with thickness less than 6.35 mm (1/4 in.) Or to be confident they may create a mock-up coupon for welding testing.
However, do not forget that by welding with low heat input, the material will cool faster (Fast Cooling Rate) and may cause the structure of the material to break easily.