Weld neck flange is a kind of flange. As parts, two flanges can be used for connecting the end of a pipe to the end of another pipe, tightly fastened by bolts through holes around flange periphery. Weld neck flange, gasket and fasteners can be collectively called flange joint. Flange joint is an indispensable component in some equipment, pipe fittings, valves, etc.
Weld neck flange is composed of a circular fitting, with a protruding rim around the circumference and holes for tightly connecting to another flange by bolts. They are widely applied in various fields and industries, and should be used in accordance with application scope and allowable conditions. For instance, they can be used in steel pipe connection with nominal pressure of no more than 2.5MPa. Hence, they play an important part in pipeline connection.
In the process of producing weld neck flanges, billets during cold forging go through deformation and work hardening, resulting in high load which is imposed on forging dies. So, it is necessary to use high strength forging dies as well as hard lubricating films with abrasion assistance and anti-bonding property. In addition, in order to avoid cracks of billets, annealing may be needed in the process of forging to ensure required deformation capacity. To keep better lubrication state, phosphating can be applied to billets. During continuous process of bar stocks and wire rods, lubricating treatment on cross section cannot be carried out, so phosphating for lubrication is being studied nowadays.
Production process of weld neck flanges:
1. Notice whether annealing temperature reaches specified temperature. Solution heat treatment is usually applied to weld neck flanges, namely annealing treatment with temperature range between 1040 °C to 1120 °C (Japanese Standard). Through observation by observation hole of annealing furnace, flanged fittings in annealing region should reach incandescent state without softening and sagging.
2. Check if water vapour retains in the furnaces that are used for processing and forging weld neck flanges. On the one hand, check if materials of furnaces are dry. Hence, before initially installing furnaces, materials of furnaces should be dried. On the other hand, check if much water retains flanged fittings to be put in furnaces, especially those flanged fittings with holes that may keep residual water, because water will destroy normal state in furnaces.
3. Inspect sealing of furnaces. Furnaces used for bright annealing applied to weld neck flanges should be sealed without exposure to the air outside. Hydrogen serves as shielding gas and there is only one exhaust port used for lighting discharged hydrogen. Soapy water can be applied to every joint or clearance to inspect if gas escapes, especially inlets and outlets of furnaces for pipe fittings where seal rings are easy to wear and need to be regularly replaced.
4. Check shielding gas pressure. To prevent minor leakage of weld neck flanges, shielding gas in furnaces should be kept within certain positive pressure. If hydrogen is used as shielding gas, hydrogen is usually required to be more than 20kBar.
5. Inspect annealing atmosphere. Pure hydrogen is usually used for annealing atmosphere of weld neck flanges, with gas purity of over 99.99%. But if inert gas is also included in annealing atmosphere, purity of hydrogen can be reduced. It should be noted that too much oxygen and water vapour cannot be included in hydrogen.