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Post-Processing Welded Parts

20 March, 20 4:52 pm · Leave a comment · Geoff Campbell
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miller proheat 35 liquid cooled on pipe

In welding, like in many other manufacturing and fabrication processes, the process is not complete until the necessary post-processing has been carried out. Post-weld operations are usually performed for reasons such as improving mechanical properties, relieving stress, and improving aesthetics. The two most common Post-weld operations are Post-Weld Heat Treatment (PWHT) and Finishing.

Post-Weld Heat Treatment

During welding, the welded materials are exposed to very high temperatures that can cause micro-structural changes in them. Also, residual stresses build up in welded materials when they are allowed to cool naturally.  If left unaddressed, these stresses and structural changes can severely compromise the mechanical properties of a material and can lead to failure during use. To prevent this, PWHT is required for welded parts. There are two major types of Post-weld heat treatment and they are as follows.

Post heating

Post heating is usually carried out to prevent Hydrogen Induced Cracking (HIC). HIC results from the permeation of materials by high levels of ambient hydrogen during welding. In Post heating, the welded material is heated to a specified temperature and held at this temperature for a specified period. This process allows the hydrogen to diffuse out of the welded area, thus preventing HIC. Post heating is carried out immediately after welding before the material cools.


In this process, the welded material is first allowed to cool. After this, it is heated to a specified temperature and held at this temperature for a specified amount of time. The material is then cooled gradually at a specified rate. As its name implies, stress relieving is done to relieve stresses that may have built up during welding and natural cooling.

The heat required in both PWHT processes is usually provided by heating systems. While several heating systems can be used for this purpose, Induction heaters such as the Miller Induction Heating Systems are highly recommended. These systems provide uniform heating, precise temperature control, power efficiency, and many more.

Stress relieving

It is important to note that most but not all materials require PWHT. The higher the content of carbon or any other alloying element in a  material, the more likely it will need PWHT. Similarly, the thicker the material, the more PWHT is required. The required temperatures and time for different materials are covered by codes and standards.
induction heating plate with miller proheat - infrared image

Finishing

Welding typically results in a visible weld seam along the areas that have been welded. Even machines as highly precise as the Miller TIG welder series produce visible, albeit very small, weld seams. These affect the appearance of the welded part.

Finishing operations are carried out to improve the aesthetic appearance of welded material. In some cases, they are done to improve the dimensional accuracy of a part.

Finishing involves two basic steps; grinding and polishing.

Grinding involves using an abrasive to level the welded area to be consistent with the surface of the material. This can be done using flap wheels, fibre discs, flap discs, or grinding wheels, depending on the type, shape, and size of the welded material, as well as the quality of finishing required.

Polishing typically takes place after grinding. For this process, gentler abrasives are used together with polishing compounds to produce a very neat surface finish. In some cases, it’s impossible to identify the welded joint after finishing.

Welding Quality Assurance & Quality Control Processes

16 December, 19 3:28 pm · Leave a comment · Geoff Campbell
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welding inspection

Quality Assurance

Quality Assurance (QA) is a set of defined processes for systematic monitoring and evaluation to assure product quality.

Quality Control

Quality Control (QC) is the process of confirming that the product meets the specifications. It includes the checking and testing of manufacturing procedures as well as the final products. The results from these tests are compared with a set of defined acceptance criteria. By carrying out QC testing during manufacturing, defects can be identified in a timely manner, allowing for the product flaw to be rectified and if required, adjustments to be made in the manufacturing process to prevent further defective output.

In welding, QA/QC plays a vital role in ensuring sound and reliable welds are produced and in minimizing rework.
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A Solution to the Skilled Welding Labor Shortage

31 October, 19 9:57 am · Leave a comment · Geoff Campbell
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In This Article: Welding Labour Gap  >  Cobots  >  The BotX Welder  >  Welding Mobile App  >

An Industry In Distress

The manufacturing industry is in distress. There is a shortage of skilled talent and this gap is only widening. While manufacturing companies are able to make goods faster and cheaper than ever, there is a growing lack of skilled manufacturing employees to ensure that production continues. Industry projections from Deloitte and the Manufacturing Institute, among other industry analysts, predict that over the next decade, more than 2 million manufacturing jobs will go unfilled across the U.S.
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Induction Heating vs Other Methods

29 April, 19 4:48 am · Leave a comment · Colin Brown
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Pre-weld and post-weld heat treating is critical for many welding operations. Without proper thermal manipulation, welds and heat affected zones can have mechanical properties that are undesirable. Worse yet, inadequate heat treatment can result in cracks and devastating weld failures. While temperature and time are the primary concerns when heat treating a weld, the heating method should also be considered diligently when selecting a process. Induction heating is one of the most popular types of heat treating methods, and rightfully so. The benefits of induction heating are many, and Red-D-Arc has the equipment you need to successfully implement an induction heat treating operation for your projects.
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Welder shortage: Key is efficiency, not automation

02 April, 19 1:31 pm · Leave a comment · Colin Brown
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Note: This article first appeared in BIC Magazine

In industry, a growing trend is the idea to use orbital welding as a solution to the mounting problem of welder shortages. It is a well-known fact there are just not enough pipeline welders to go around (no pun intended). By 2020, the American Welding Society expects the U.S. will face a shortage of 290,000 welders. Companies in other business sectors — from food service companies to banks — attempt to solve labor issues and increase efficiencies by utilizing automation to replace workers. Is automation, specifically orbital welding in this case, the way to improve operating factors and productivity?

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Airgas, an Air Liquide company, is the nation's leading single-source supplier of gases, welding and safety products. Known locally nationwide, our distribution network serves more than one million customers of all sizes with a broad offering of top-quality products and unmatched expertise.