BPHE Nozzle Failure After Secondary Soldering

Original project record

Failure Caused by Overheating During Secondary Soldering – Damage to Brazed Structure at Nozzle Connection

This technical note explains a common failure mechanism in copper-brazed plate heat exchangers (BPHE) where uncontrolled secondary soldering at the nozzle connection introduces localized overheating and weakens the original brazed joints, leading to leakage.

• Overview
• Observed Failure Characteristics
• Root Cause Analysis
• Why This Is Not a Manufacturing Defect
• Preventive Recommendations
• Engineering Conclusion

Overview

Video evidence: leakage location and brazed joint damage pattern after secondary nozzle soldering.

In copper-brazed plate heat exchangers, the internal plate stack is joined through a controlled vacuum brazing process. The integrity of the unit depends on maintaining the metallurgical stability of these brazed joints.

However, secondary soldering or welding operations performed at the nozzle connection can introduce excessive localized heat. Without temperature protection, overheating can re-melt or weaken the original brazed copper bond near the nozzle area, resulting in leakage.

Observed Failure Characteristics

Based on inspection and leakage pattern, the key observations were:

• Leakage at the nozzle interface
• No signs of corrosion-induced degradation
• No evidence of pressure overload
• Localized joint weakening around the connection area

The failure mode is consistent with thermal degradation of the brazed structure rather than a material or manufacturing defect.

Root Cause Analysis

1) Copper-Brazed Plate Structure

Copper-brazed plate heat exchangers are manufactured in a vacuum furnace under controlled conditions (typically around 1100°C). The copper bonds:

• Join the plates
• Seal the internal channels
• Provide structural integrity

After brazing, the copper joints remain stable only within defined thermal limits during field operations and modifications.

2) Secondary Soldering Without Thermal Protection

During external nozzle soldering, the following risk factors were present:

• Direct flame heating was applied
• No heat sink or cooling protection was used
• Local temperature exceeded the safe threshold

Excessive localized heat can:

• Re-melt or soften internal brazed copper
• Disturb capillary bonding
• Create micro-voids
• Reduce joint strength

This compromises the seal between the plate pack and end plate near the nozzle area.

3) Mechanism of Leakage

When the brazed seam close to the nozzle is thermally disturbed:

• Micro-cracks develop
• Capillary seals weaken
• Internal cross-leakage or external seepage appears

Why This Is Not a Manufacturing Defect

The original brazed structure is stable under specified operating conditions. The observed failure pattern matches:

• Localized overheating introduced after production
• Metallurgical weakening of the brazed joint near the nozzle
• Failure concentrated at the modified connection zone

Preventive Recommendations

To prevent overheating-related leakage during nozzle work:

• Use temperature-controlled soldering techniques
• Apply heat sinks or cooling wraps during nozzle soldering
• Avoid prolonged direct flame exposure
• Monitor surface temperature during the operation
• Prefer factory-assembled connection options when possible

Engineering Conclusion

Copper-brazed plate heat exchangers are sensitive to uncontrolled secondary heating at nozzle connection points.

This case is consistent with overheating during soldering without adequate thermal protection , which degraded the original brazed joints and caused leakage near the nozzle area.

Proper temperature management during field modifications is essential to maintain brazed joint integrity and long-term reliability.