Frequently Asked Questions
Outline procedure for repair of a ½Cr-½Mo-¼V casting
- Preheat uniformly to a minimum of 250°C preferably in a furnace.
- Use basic low hydrogen electrodes of 2¼ Cr-Mo type, baked at the time and temperature recommended by the manufacturer to give less than 5mls H2/100gm weld metal.
- Butter excavation surfaces with 2.5mm dia. electrodes.
- Deposit second layer with 3.2mm dia. electrodes.
- Half fill with 4.0mm electrodes if the repair is deep (i.e. greater than approximately 30mm).
- Hot grind weld toes at the preheat temperature.
- If the excavation is large, carry out an intermediate stress relief at 700°C allowing 1 hour at temperature for each 25mm thickness; heating and cooling rates must be controlled to a maximum of 25°C per hour.
- Fill completely with 4mm dia. electrodes.
- Repeat steps (6) and (7).
- Carry out NDT on the repaired casting - as a minimum, both MPI (magnetic particle inspection) and ultrasonics should be used.
Excavations should be flared out at the ends to a slope of around 4:1 and corners ground to give a radius of some 6mm. The included angle of the sides of the excavation should be in the order of 60°. If thermal cutting processes are used to remove the defect then preheat is required and a minimum of 2mm should be ground or machined away from the excavation to remove any HAZ after cutting. This should be followed by MPI as a minimum to confirm that the defect has been completely removed.