Published on 30-Dec-2021

How is the brazing procedure qualification done?

How is the brazing procedure qualification done?

What is brazing?

Brazing is a process of joining dissimilar metals, whereas welding is a process of joining similar metals. In this blog, we can see about some of the details in Brazing procedure qualification

Brazing involves melting filler metal and flowing over the joining surfaces. The filler metal used is generally of a lower melting point than the base metal. the base metal is just preheated to make it readily fusible.

The filler metals flow into the gaps of closed fitted base metals by capillary action.

The different types of brazing are :

Torch Brazing
Furnace Brazing
Induction Brazing
Resistance Brazing
Dip Brazing

What are the heating methods available in brazing?

There are many heating methods available to accomplish brazing operations. The most important factor in choosing a heating method is achieving efficient transfer of heat throughout the joint and doing so within the heat capacity of the individual base metals used. The geometry of the braze joint is also a crucial factor to consider, as is the rate and volume of production required. The easiest way to categorize brazing methods is to group them by the heating method. Here are some of the most common:

Torch brazing
Furnace brazing
Induction brazing
Dip brazing
Resistance brazing
Infrared brazing
Blanket brazing
Electron beam and laser brazing
Braze welding

These heating methods are classified through localised and diffuse heating techniques and offer advantages based on their different applications.

How does the brazing process take place?

The Brazing Process required a qualified Brazing Procedure (similar to a WPS, Welding Procedure Specification) and a Brazing operator qualification (similar to a welder qualification certificate ).

Essential Parameters for Brazing

These are the important parameters for brazing:

Base Metal
Filler Metal
Flux, Gas
Flow Position
Joint Design
Post-Braze Heat Treatment Technique

Brazing Procedure & Approval

The standard ASME BPVC, Section IX has qualification variables and ranges for brazer qualification and brazing procedure qualification.

ASME BPVC Section IX, Article XII gives us the guidelines for Brazing Procedure Qualifications and
Article XIII for Brazing Performance Qualifications,
Non-mandatory Appendix B – sample format for procedure preparation
QB-482 – Suggested Format for Brazing Procedure Specification
QB-483 – Suggested format for Brazing Procedure Qualification Record
QB-484 – Suggested format for Brazing Operator Performance Qualification

The Base metals for brazing have P number as shown below & P.No’s can be selected from TableQW/QB-422 :

Steel & Steel Alloys – P.No.101 through P.No.103
Aluminium & Al Alloys – P.No.104 through P.No.105
Copper & Copper Alloys- P.No.107 through P.No.108
Nickel & Nickel Alloys – P.No.110 through P.No.112
Titanium & Titanium Alloys – P.No.115
Zirconium & Zirconium Alloys – P.No.117

Procedure Qualification Process:

The procedure qualification process is done using the following steps

A sample test coupon is prepared of dimensions sufficient for performing all the tests, the range of thickness qualified is given in QB-451.

 

Qualification of Pipe also qualifies plate.
Perform the required tests on the brazed specimen, ex: 2 Tensile & 4 Bend tests as given in the table.
Or For Lab Joints, perform 2 Tensile and 2 Peel off test
Similarly, all brazers are made to braze a sample test coupon and tests are made as per table QB-452
Note that peel test may be substituted by sectioning tests, where it is impractical to perform.

Common Brazing Techniques

→ Torch Brazing: Torch brazing is by far the most common method of mechanized brazing in use. It is best used in small production volumes or in specialized operations, and in some countries, it accounts for a majority of the brazing taking place. There are three main categories of torch brazing in use: manual, machine, and automatic torch brazing.

→ Furnace Brazing: Furnace brazing is a semi-automatic process used widely in industrial brazing operations due to its adaptability to mass production and the use of unskilled labour. There are many advantages of furnace brazing over other heating methods that make it ideal for mass production. One main advantage is the ease with which it can produce large numbers of small parts that are easily jigged or self-locating. The process also offers the benefits of a controlled heat cycle (allowing the use of parts that might distort under localized heating) and no need for post braze cleaning. Common atmospheres used include: inert, reducing or vacuum atmospheres all of which protect the part from oxidation. Some other advantages include low unit cost when used in mass production, close temperature control, and the ability to braze multiple joints at once. Furnaces are typically heated using either electric, gas or oil depending on the type of furnace and application. However, some of the disadvantages of this method include high capital equipment cost, more difficult design considerations and high power consumption.

→ Silver Brazing: Silver brazing, sometimes known as hard soldering, is brazing using a silver alloy based filler. These silver alloys consist of many different percentages of silver and other metals, such as copper, zinc and cadmium.

→ Vacuum Brazing: Vacuum brazing is a material joining technique that offers significant advantages: extremely clean, superior, flux-free braze joints of high integrity and strength. The process can be expensive because it must be performed inside a vacuum chamber vessel. Temperature uniformity is maintained on the workpiece when heating in a vacuum, greatly reducing residual stresses due to slow heating and cooling cycles. This, in turn, can significantly improve the thermal and mechanical properties of the material, thus providing unique heat treatment capabilities. One such capability is heat-treating or age-hardening the workpiece while performing a metal-joining process, all in a single furnace thermal cycle.

→ Dip Brazing: Dip brazing is especially suited for brazing aluminium because air is excluded, thus preventing the formation of oxides. The parts to be joined are fixtured and the brazing compound is applied to the mating surfaces, typically in slurry form. Then the assemblies are dipped into a bath of molten salt (typically NaCl, KCl and other compounds), which functions as both heat transfer medium and flux. Many dip brazed parts are used in heat transfer applications for the aerospace industry.

Conclusion:

We hope this blog article has helped you understand the brazing procedure specification process. Do you want to know more about the rest of the important aspects about the NDT industry? Check out One Stop NDT

We, at One Stop NDT always strive to create awareness to the NDT Market (Equipment Manufacturers, service providers, distributors, plant operators, NDT professionals etc) about the New Development and products & Services availability in Global Market and to provide them with direct access to interact and explore on the possibilities of helping and working together.



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