Alloy 622 Water Wall Panels Boiler Alloy 625 686 3mm

The excellent corrosion resistance of Inconel 625 is due to the presence of molybdenum, niobium and refractory metal solution. The presence of nickel and chromium in Inconel 625 provides excellent oxidation resistance. Nickel and molybdenum prevent non-oxidative erosion, while niobium stabilizes the alloy to prevent sensitization during welding.

Inconel 625 is a high strength material with extremely high corrosion resistance and oxidation resistance. Therefore, can be competent for aerospace and chemical processing industry. This super alloy has high mechanical strength and hardness at low temperatures of about 2000oF / 1093oC. The alloy has excellent resistance to chloride ion stress corrosion cracking. It is nonmagnetic in nature. Due to its toughness, alloy 625 is suitable for degrading chloride ions.

The most common problem in surfacing is cracking. The main methods to prevent cracking are as follows

1. Preheat before welding, control interlayer temperature and slow cooling after welding

2. Stress relief heat treatment after welding

3. Avoid multi-layer surfacing and use low hydrogen surfacing electrode

4. If necessary, build up the transition layer between the surfacing layer and the base metal (use the electrode with low carbon equivalent and high toughness)

Attention must be paid to butt welding:

1. According to the use requirements, reasonable selection of surfacing alloy

2. Reduce the dilution ratio of base metal as much as possible

3. Improve productivity

4. It is expected that the hardfacing metal and base metal have similar expansion coefficient and phase transformation temperature

Inconel overlay thickness must maintain a minimum thickness of 0.070". To maintain surface smoothness the cross-sectional inconel thickness minimum and maximum delta shall not be greater than 0.020". The use of a permascope every 100 linear feet (approximately every 5th tube) shall be utilized to monitor overlay thickness. All thickness measurements shall be recorded and submitted to Covanta with final documentation. If test results indicate less than 0.070" overlay thickness and a greater than 0.020" delta between minimum and maximum thickness, the supplier shall take the appropriate additional testing, monitoring and production measures necessary to assure that the thickness and surface smoothness is maintained in the desired range and that any deviations shall be minor in magnitude and minimum in frequency.