A weld neck flange (also known as a high-hub flange and tapered hub flange) is a type of flange. There are two designs. The regular type is used with pipes. The long type is unsuitable for pipes and is used in process plant. A weld neck flange consists of a circular fitting with a protruding rim around the circumference. Generally machined from a forging, these flanges are typically butt welded to a pipe. The rim has a series of drilled holes that permit the flange to be affixed to another flange with bolts.
Such flanges are suitable for use in hostile environments that have extremes of temperature, pressure or other sources of stress. The resilience of this type of flange is achieved by sharing the environmental stress with the pipe with which it is welded. This type of flange has been used successfully at pressures up to 5,000 psi.
Welding Neck Flanges are easy to recognize at the long tapered hub, that goes gradually over to the wall thickness from a pipe or fitting.
The long tapered hub provides an important reinforcement for use in several applications involving high pressure, sub-zero and / or elevated temperatures. The smooth transition from flange thickness to pipe or fitting wall thickness effected by the taper is extremely beneficial, under conditions of repeated bending, caused by line expansion or other variable forces.
These flanges are bored to match the inside diameter of the mating pipe or fitting so there will be no restriction of product flow. This prevents turbulence at the joint and reduces erosion. They also provide excellent stress distribution through the tapered hub and are easily radiographed for flaw detection.
This flange type will be welded to a pipe or fitting with a single full penetration, V weld (Buttweld).
To produce Welding Neck flange’s forging billet in cold forging deformation and strain hardening, the forging die under high load, therefore, need to use the high strength of the forging die and using hard of lubricant to prevent wear and adhesive processing method. In addition, to prevent crack in billet, intermediate annealing when necessary to ensure deformation ability. To keep good lubrication condition, phosphating of billet. In a continuous process with bar and wire rod, and the current of cross section is not lubrication processing, are studying the possibility of phosphating lubrication method is used.
Production and processing process of Welding Neck flange
Whether a, annealing temperature reaches the temperature. Welding Neck flange processing is commonly take solid solution heat treatment, also is the people of the so-called “annealing” usually, temperature range is 1040 ~ 1120 ℃ (Japan standard). You can also through observing hole of annealing furnace and annealing the flange pipe fittings shall be the state of incandescent, but did not appear to soften prolapse.
Second, the Welding Neck flange machining casting furnace water vapor. On the one hand, check whether the furnace material is dry, the first furnace, furnace material must be dry; The second is whether the flange into the furnace pipe residual too much stain, special flange pipe fittings above if there is one hole, don’t slack and went in, or we’ll get the furnace atmosphere all destroyed.
Three, furnace body sealing. Welding Neck flange bright annealing furnace should be closed, cut off from the air outside; Adopting hydrogen gas as shielding gas, only a vent is (used to ignite the discharge of hydrogen). Check method can wipe with soap and water in each joint cracks in annealing furnace, look to whether running; One of the most easy to run gas place is where the annealing furnace into the pipe and the pipe, the place of sealing ring particularly easy to wear, often should check in regularly.
Fourth, protect gas pressure. Micro holes in order to prevent the Welding Neck flange, protective gas should maintain a positive pressure in the furnace, if the hydrogen gas protection, general requirements above 20 kbar.
Five, the annealing atmosphere. Pure hydrogen Welding Neck flanges are generally used as the annealing atmosphere, atmosphere best is more than 99.99% purity, if the other part is an inert gas atmosphere, can also lower purity, but absolutely can’t have too much oxygen and water vapor.
Source: Yaang Pipe Industry Co., Limited (www.yaang.com)