Nick Verberkmoes

Nick Verberkmoes

After more than twelve years of experience in the oil and gas industry, Nick decided to continue as an independent entrepreneur. In this way he can use his knowledge and experience in a broad way.

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How the choice of the welding consumable can make or break your weld

Introduction

Questions will arise once a steel construction fails, tears apart, ruptures or collapses especially when it causes heavy damages with high costs or even worse; fatal casualties. Obvious questions such as why this happened, what or who caused this will be asked. What if it turns out that the failure can be related to weld metal and the choice of welding consumable? 

The methodology for selecting and buying the right welding consumable will be outlined in two articles. In this first article we dive into technical aspects of selecting welding consumables. 

Selection criteria

To select the right welding consumable there is a set of questions we should answer:

  • What is the weld exposed to during its lifetime?
  • What are the mechanical and chemical requirements?
  • What is the applicable welding process?
  • What is the welding position with its progression?
  • What type of consumable?

Once all five technical questions are answered the search for the welding consumable can start. Let us guide you through the best way to collect the answers. 

What is the weld exposed to during its lifetime?

In order to create a weld which is safe and sound we must understand to what the weld is exposed to during its lifetime and to what extent it is exposed. 

  • What type of forces apply? Static and/or dynamic? 
  • What is the load?
  • Is the weld subjected to pressure? If so, what is the pressure? 
  • Does the weld encounter any sub-zero or high temperatures? 
  • Is there a certain type of corrosive environment, like ocean waters or chlorides. 

Summarizing, we need to know the strength, pressure, temperature and environment to which the weld is exposed to.  All this information should be provided by the engineers who design the structure.  

What are the mechanical and chemical requirements?

The mechanical properties are often a discussion and can lead to failure. Therefore, we generally seek information about the Tensile Strength, Yield Strength, Elongation and Toughness of the welding consumable. Hardness is generally only interesting when hardened surfaces are required, like wear plates in dredging machines. As a rule of thumb, the strength of a weld should be similar to the lowest strength base material. In most cases engineers do not calculate with extra capacity of a weld and consider it as equal to the base materials.

The chemical composition requirements are equally important to a weld as the mechanical properties are. Still, they are often overlooked and not considered during selection. For chemical composition we may use the same terminology as used in metallurgy, such as carbon-manganese, low alloy and stainless steels. Where carbon (C), manganese (Mn), silicon (Si), chrome (Cr), nickel (Ni) and molybdenum (Mo) are the most predominant elements. It is often said that the weld metal should have the same requirements as the base material. Which we cannot blindly follow, however it is a good start for deciding where to go to in the land of welding consumables.

What is the applicable welding process?

First thing to find out if welding is performed indoors or outdoors. When welding outdoors and sufficient countermeasures on environmental influences cannot be taken, this may limit the selection of welding processes. Secondly, we need to know what type of welding equipment is available to us at the location where we produce our weld. This should lead to the applicable process such as SMAW, MIG/MAG (GMAW), TIG (GTAW) or SAW.

What is the welding position with its progression?

Obviously, we must understand with what welding position and progression we are working; overhead, flat, horizontal, vertical uphill or downhill. If it is overhead or vertical downhill some processes and/or welding consumables are not suitable. Bear in mind that most manual handled weld processes can weld in all positions, but the consumables may not give the right result. For instance, when welding vertical uphill with a rutile flux cored wire, the slag of the flux cored wire supports the weld puddle, which is not the case when welding vertical downhill.  

What type of consumable?

In the world of welding consumables, these can be considered the general consumables and process combinations:

  • Electrodes for SMAW, 
  • Solid welding wire for TIG(GTAW), MIG/MAG (GMAW) and SAW, 
  • Flux cored welding wire for MIG/MAG (FCAW) and SAW,
  • Flux powders for SAW. 

Simplified it can be stated that the welding process derives the type of consumable.

So, in order to select the right welding consumable, we must understand the exposure of the weld in its environment, mechanical properties, chemical composition, welding process, welding position and the progression. If this all is known, we can start selecting the consumables from the manufacturers. 

Click here to read the article about the procurement of welding consumables. 

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