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Welding repairs shouldn't be over complicated. It is not necessary to have Welding Procedure Specifications, which specify the compliance criteria for how a weld is to be done, for typical routine crack repairs. This is because;
a) most crack repairs vary in depth and preparation profile - they are not at all like a prepared joint for fabrication
b) It is not feasible for to select the appropriate procedure(s) for each repair - mine simply don't have the technical experts to manage this
c) there is no way to manage compliance to a procedure without having a welding supervisor present
d) It is generally not necessary to comply with exact welding parameters for crack repairs - it is the effectiveness of the repair that is important
e) most welders won't bother with the procedure - they already know what to do!
Therefore, we have simplified the technical welding management by taking a new approach, whereby there is a Universal Repair Parameter Sheet for each of the 3 common classes of materials.
For each material group, the URPS provide the essential parameters which are
Working Temperature range (ie minimum preheat to maximum interpass)
Recommended consumable type for the various processes
Material Groups
Based on welding metallurgy fundamentals, the typical materials used in most mining equipment can be simplified into 3 groups
1) Structural Steels
2) High Strength Structural Steels
3) Mild Steel Castings
Anything that is not in these groups should have a specific repair weld procedure.
When carrying out a weld repair, the essential parameters (independent of the welding process) are the working temperature and consumable. The Welder must be able to independently "dial in" the appropriate settings for the process, consumable, position, joint type and welding machine condition.
Working Temperature
Preheat is often misunderstood. And interpass temperature is rarely considered. Therefore, we have simplified the whole temperature management concept by defining the "Working Temperature". If it is not within the working temperature range, no welding "work" should be carried out. This reinforces that the minimum Working Temperature must be maintained for the duration of the repair.
In AS1554, the minimum preheat is determined based on a combination of material group, heat input, and combined joint thickness. While good for design and fabrication specification, this is just too complicated for repair work. Rather than having a complicated method to figure out the minimum working temperature, we have gone back to fundamental welding and metallurgical principles and set simple minimum temperatures that are easy to remember and apply. These have been fully validated via extensive welding trials and metallurgical testing.
Consumable
The selection of the right consumable can be based on many factors, but fundamentally most mine sites will have a limited selection available. The key is to appropriately match the consumable strength to the material properties.
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