The factors that affect the brightness of stainless steel butt-welded elbows during annealing, the brightness of the products after annealing determines the quality of the products. There are many factors that affect its brightness, and the five important factors are:
- Ensure that the annealing temperature reaches the specified level. The heat treatment of stainless steel butt-welded elbows is generally solution heat treatment, commonly referred to as "annealing," with a temperature range of 1040~1120°C (as per Japanese standards). This can also be observed through the annealing furnace, where the stainless steel butt-welded elbows in the annealing area should appear incandescent but not softened or sagging.
- The annealing atmosphere typically uses pure hydrogen, with a purity of over 99.99%. If an inert gas is used for part of the atmosphere, the required purity can be slightly lower, but it must not contain excessive oxygen or water vapor.
- The sealing of the furnace body is crucial. The bright annealing furnace should be sealed and isolated from outside air; if hydrogen is used as the protective gas, only one exhaust port should be open (to ignite the discharged hydrogen). To check for leaks, wipe the joints of the annealing furnace with soapy water to see if there is any gas leakage. The areas where the pipe enters and exits the furnace are particularly prone to gas leakage, as the sealing rings in these areas wear out easily and should be inspected and replaced frequently.
- To prevent micro-leakage, the protective gas in the furnace should be maintained at a certain positive pressure. Additionally, the hydrogen protective gas is generally required to be above 20 kPa.
- Water vapor in the furnace should be carefully controlled. First, check if the furnace body material is dry, especially during the initial installation, when the furnace body material must be thoroughly dried. Second, ensure that the stainless steel pipe entering the furnace is free from excessive water stains, particularly if there are any holes in the pipe, as water ingress can completely destroy the furnace atmosphere.
Generally, when the furnace is operating normally, the stainless steel pipe should begin to shine approximately 20 meters after entering the furnace. This should be observed when the product leaves the factory.
