Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers



Last updated: February 15, 2019

What Does Brazing Mean?

Brazing is a method of joining material that is an alternative to welding. Brazing creates the coalescence of metallic materials by initially heating them to the process temperature, as well as through the use of filler metals having a liquid state above 450°C, and below the melting point of the base metals being joined.

The study of brazing is important because its advantages include:

  • Strong joints with good mechanical strength
  • Corrosion resistance of joints when correct filler materials are used
  • Lower temperatures and consequently lower cost than welding
  • Base metals' properties are retained.
  • Dissimilar materials can be joined.

Corrosionpedia Explains Brazing

The main difference between brazing and welding is in the level of heating. Brazing does not heat to melt the base metals to be joined. Therefore, the process temperatures are much lower than the melting points of these base metals, and therefore much lower than welding temperatures. When brazing is done below 450°C, it is called soldering.

The brazing process joins materials through creation of a metallurgical bond between the base metal surfaces and filler metal. It is through capillary action that the filler metal in a molten state is drawn into the joint to create a metallurgical bond. Heat is applied to the metals to be joined. Then the filler metal is drawn into the gap of the parts to be joined. Melting of filler is instantaneous. This ensures a strong joint.

While choosing the filler metal, it is important to consider the corrosion protection the filler material offers. Filler materials with good corrosion resistance include:

  • Gold
  • Palladium
  • Chromium
  • Nickel

Filler is produced in several forms:

  • Wires
  • Strips
  • Paste
  • Powders

When hot metals come in contact with oxygen, oxides are readily formed. These oxides prevent the molten filler metal from forming a metallurgical bond with base metals. This results in lower joint strength. Flux is an additional chemical that is used to shield the base metal joint surfaces from air ingress, and thus prevents metal oxide formation on brazing joints.

The base metals surfaces being joined need be thoroughly cleaned before the brazing process. Flux residue is cleaned by quenching and soaking in hot water. Special chemical cleaners are also available.

The joint strength depends on:

  • Strength of base metals
  • Joint size and clearance (clearance can increase joint strength)
  • Strength of filler metal

Brazing applications include:

  • Vacuum interruptors
  • Aviation
  • Transport
  • Construction
  • Medical equipment
  • HVAC (heating, ventilation, air conditioning)
  • Art
  • Jewelery

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