Welding Process Notes for Q345R

Welding Process Notes for Q345R (Suitable for Pyrolysis Damping Tank / Steam Drum)

Adhering to the core principles of equal strength matching, stress relief and defect prevention, and meeting the requirements of pressure vessel and pyrolysis working conditions, the key points before, during and after welding shall be strictly controlled in compliance with pressure vessel welding specifications:

I. Pre-welding Preparation

Welding material matching: Select E5015/E5016 alkaline electrodes for manual welding; use ER50-6 welding wire + 80% Ar + 20% CO₂ mixed gas for gas metal arc welding. Low-strength substitutes are strictly prohibited.

Surface cleaning: Remove oil, rust and carbon black from the groove and 20-30mm of its both sides to ensure no moisture or impurities remain.

Preheating requirements: Weld at room temperature for base metal with wall thickness ≤16mm; preheat to 80-150℃ for 16-32mm; preheat to 150-200℃ for wall thickness ＞32mm or welding at low temperature (＜5℃).

Groove processing: Adopt mechanical processing for V-groove/double V-groove to ensure full penetration and avoid hardened layer.

II. Welding Process

Standard welding: Adopt multi-layer and multi-pass welding with slag removal and grinding after each layer; strictly control welding current and voltage to avoid burn-through and incomplete penetration.

Stress reduction: Adopt segmental skip welding for long welds and discontinuous welding for key joints to prevent tank deformation and stress concentration.

Protective measures: Provide wind protection for gas metal arc welding and stop welding when humidity ＞80%; the fillet weld size of corner joints shall be not less than the minimum thickness of base metal without undercut.

Welder qualification: Welders must hold a pressure vessel welder certificate with the qualified items matching the actual welding operation.

III. Post-welding Treatment (Core Step)

Stress relief: Prioritize local heat treatment (550-600℃, hold for 1 hour per 25mm wall thickness, slow cooling ≤100℃/h); hammer peening is applicable for stress relief of thin-walled small parts, adapting to the intermittent thermal fatigue working conditions.

Cleaning and inspection: Remove welding slag and spatter, grind the surface smooth without sharp edges; ensure no surface defects such as blowholes and cracks.

Non-destructive testing (NDT): Conduct 100% radiographic testing (RT ≥ Grade Ⅱ) for butt welds; implement magnetic particle testing (MT) / penetrant testing (PT) ≥ Grade Ⅰ for corner joints / nozzle joints. Rework for the same position shall not exceed 2 times.

Anti-corrosion connection: For inner wall coating construction under high-sulfur working conditions, conduct the operation after passing the NDT and thicken the coating at welds.

IV. General Prohibitions

Rapid cooling with cold water is strictly prohibited after welding to prevent cold brittleness.

Use special welding materials (e.g., A302) for dissimilar steel welding (e.g., connecting with stainless steel accessories); direct use of carbon steel or stainless steel electrodes is strictly prohibited.

Keep complete welding records for future reference to meet compliance requirements.