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Welding and cutting defects
Welding and cutting defects do sometimes occur, even when care is taken to try and avoid them. Understanding what the main causes of these defects are is of fundamental importance in ensuring they do not arise.
It is logical that we should know what the cost of completing a cut or weld is, but do you know how to work out the cost?
Several factors must be taken into account to give an accurate cost, these include:
- power consumed
- consumable used
- labour cost
- gas cost
Should depreciation of equipment or purchase price be considered?
Weld testing can be divided into two main areas; destructive and non-destructive testing methods.
In destructive testing, the sample of material or weld is snapped, broken and pulled apart by numerous techniques to gather data regarding the strength, toughness and hardness of the component.
With non-destructive testing, as the name suggests, no physical damage occurs to the component.
Techniques such as visual inspection, x-ray and ultrasonic testing are some of the most commonly used methods.
Welding engineering is a very broad topic area covering topics such as joint design, weld preparations and welding positions.
Welding procedures are documents used by the welding engineer to guide the welder in the choice of consumable and welding conditions. They also carry other valuable information such as when preheating is required.
Many standards and classifications are used by the welding industry, but are they easy to understand? For example, MMA electrode manufactures and suppliers quote electrodes as being types E7018 but what does this mean? In fact, the numbers give an indication of the strength of the weld metal which will be deposited by the electrode and the type of coating the electrode has.
When a weld is produced both the welding conditions used and the composition of the shielding gas can have a significant affect on the metallurgy.
When welding stainless steels, carbon can be added to the weld metal through the decomposition of carbon dioxide used in the shielding gas. If too much carbon is added then this can affect the corrosion properties of the stainless steel.
There is a range of different heat treatments employed on materials before, during and after welding takes place. Preheating is a method used to prevent hydrogen cracking taking place. Heat treating a material can also be a method of reducing or removing stress which may have built up in a component either through forming or welding.
Other topics covered include basic electricity, which is fundamental in understanding how arc welding power sources operate.
Hardfacing, surfacing and cladding
Hardfacing, surfacing and cladding are all surface treatments carried out on components to improve their operation.
Hardfacing the teeth of digger buckets is carried out to improve the wear resistance of these components.
Cladding of the internal surfaces of a vessel with stainless steel panels can mean that the structural parts of the vessel can be made out of a material which is cheaper, but the overall corrosion resistance and working life is not compromised.