According to API 1104, 22nd Edition (2020), and its amendment for in-service welding, hot tap welding on pressurized pipelines demands rigorous control of heat input and cooling rate to prevent burn-through or hydrogen cracking.
A common failure mode is excessive heat input that weakens the pipe wall under pressure. The standard specifies maximum heat input limits based on pipe wall thickness and internal pressure. For example, for a 6 mm wall thickness at 70% SMYS, the heat input must not exceed 1.5 kJ/mm.
Key requirements from API 1104 for in-service welding:
• Pre-weld assessment: measure wall thickness, confirm remaining wall is adequate.
• Qualified WPS: must be tested under simulated in-service conditions with flowing fluid.
• Controlled welding parameters: low heat input, stringer beads, limited electrode size.
• Post-weld cooling rate: slow cooling to avoid hard HAZ; sometimes requires preheat.
Auditors typically check that the WPS includes the actual in-service conditions (pressure, flow rate, fluid type) and that welders are specifically qualified for hot tap welding.
How does your team qualify WPS for hot tap welding on pressurized piping?
Source: API 1104, 2020