Welding Cracks
Welding cracks are a major issue in the metals fabrication industry due to the significant cost, safety and performance implications they bring. Cracks in welds occur when sections of metal are joined together using welding and they present a number of potential problems.
Cracks may form either during the welding process or shortly afterwards due to the stresses generated by the high heat of the welding process. This can lead to a weakened or fractured weld that is not structurally sound and presents a risk to personnel on the work site.
In some cases, such as with pipelines, welds must also endure hydrostatic testing before being put into service which can cause cracks to expand due to the pressure of the test fluids.
Cracks can be caused by several factors including:
• Poor preparation of the metals prior to welding
• Incorrect welding techniques
• Poor fit-up of the materials
• Excessive heat input from the weld
• Over-stressing of the weld
• Improper cooling of the weld
• Contamination of the weld area
• Inappropriate welding processes
• The material composition of the metals
The most common type of welding crack is the ‘hot-tear’ which is caused by the rapid cooling of the weld and the resulting rapid contraction of the structure. If a weld is cooled too quickly, or if the welding rod used is underpowered, then a series of cracks may appear in the weld.
To avoid welding cracks it is important to prepare the metals correctly prior to welding and ensure that the work pieces fit together correctly. It is also important to ensure that the welding process is carried out correctly and that the welding rod power is appropriate. Over-stressing of the weld should be avoided and the weld must be cooled properly.
Welding cracks can be repaired with a variety of techniques. The most common method is to fill the crack with a filler rod and then reheat the weld before allowing it to cool more slowly. This will help to mitigate the risk of further cracking.
In some cases, cracks can be prevented by using a welding process known as preheating which involves briefly heating the metal before welding. This reduces the risk of cracking due to the sudden contraction and stresses of the metal caused by the welding process.
Welding cracks can be a major source of lost production time and costs and can present a potential hazard to personnel. It is therefore important that effective measures are taken to avoid welding cracks. This includes proper preparation and fit-up of the metals, using the right welding process and controlling the cooling of the weld. Additionally, preheating can be used in some cases to reduce the risk of cracking.
A number of methods exist for the repair of welding cracks including the use of filler rod and reheating. However, prevention is always better than cure and it is important to take every precaution to ensure that welding cracks are avoided in the first place.
