Flanges are the Forged / Rolled, Machined pieces to be used in plants / installation components as a fastening / connecting / assembling service conveying media. For several decades, the world over, from the vast on-shore plants in Middle & Far East to advance North Sea Oil rigs & other installations Flanges have been on target with adequate and flexible solutions.
They are distinguished from other types by their long tapered hub and gentle transition of thickness in the region of the butt weld joining them to the pipe. The long tapered hub provides an important reinforcement of the flange proper from the standpoint of strength and resistance to dishing. The smooth transition from flange thickness to pipe wall thickness effected by the taper is extremely beneficial under conditions of repeated bending, caused by line expansion or other variable forces and produces an endurance strength of welding neck flanged assemblies equivalent to that of a butt welded joint between pipes, which, in practice, is the same as that of unwelded pipe. Thus this type of flange is preferred for every severe service condition, whether this results from high pressure or from sub-zero or elevated temperature, and whether loading conditions are substantially constant or fluctuate between wide limits.
Slip-on flanges continue to be preferred to welding neck flanges by many users on account of their initially lower cost, the reduced accuracy required in cutting the pipe to length, and the somewhat greater ease of alignment of the assembly; however their final installed cost is probably not much, if any, less than that of welding neck flanges. Their calculated strength under internal pressure is approximately two-thirds that of welding neck flanges, and their life under fatigue is about one-third that of the latter. For these reasons, slip-on flanges are limited to sizes ½" to 2 ½" in the 1500 lb standard and are not shown in the 2500lb standard.
Blind flanges are used to blank off the ends of piping, valves and pressure vessel opening. From the standpoint of internal pressure and bolt loading, blind flanges, particularly in the larger sizes, are the most highly stressed of all flange types; however, since the maximum stresses in a blind flange are bending stresses at the center, they can safely be permitted to be higher than in other types of flanges.
They were initially developed for use on small size high pressure piping. When provided with an internal weld, their static strength is equal to, but their fatigue strength 50% greater than double welding slip-on flanges. Smooth bore conditions can readily be attained (by grinding the internal weld) without having to bevel the flange face and, after welding, to reface the flange as would be required with slip-on flanges. The internally welded socket type flange is popular in chemical process piping for this reason.
They are confined to special applications. Their chief merit lies in the fact that they can be assembled without welding this explains their use in extremely high pressure services, particularly at or near atmospheric temperature, where alloy steel is essential for strength and where the necessary post weld heat treatment is impractical. Threaded flanges are unsuited for conditions involving temperature or bending stresses of any magnitude, particularly under cyclic conditions, where leakage through the threads may occur in relatively few cycles of heating or stress; sea welding is sometimes employed to overcome this, but cannot be considered as entirely satisfactory.
Lap Joint Flanges (Loose Flanges) are used with a corresponding stub-end that "inserts" in the inside of the flange. Comparing to other types of flanges, the main benefit of this type of flange is that once the pipe welds to the insert stub-end, the flange then can rotate for easier alignment of the bolting holes.
Reducing flanges are specialty flange that are most often used on projects that require the fitting together of different sized pipes. There are several types of reducing flanges including weld-neckreducing flanges, slip-on reducing flanges and threaded reducing flanges.
Applications involving high pressure and the need for a hub that is long and tapered are what weld neck flanges are most often used for. Specifying the schedule of pipe that it will be utilized for this of utmostimportance when ordering. This type of flange is excellent for use in environments involving extreme temperature fluctuations and excessive handling and bending.
Orifice Flanges are used with orifice meters for the purpose of measuring the flow rate of either liquids or gases in the respectivepipeline. Pairs of pressure "Tappings", mostly on 2 sides, directly opposite each other, are machined into the orifice flange.
Drip Rings (sometimes known as Flushing Rings) are commonly used in applications where Pligging may occur or where in-situ calibration is required without removing the instrumentfrom the process.
Spectacle blind consists of a blind and spacer. The blind is installed in between flanges to securely shutdown pipeline during leakage or maintenance. When a blind is not requird, a spacer can be installed in between flanges to continue regular operating conditions.
Spacers and Spades are part of a family referred to as Line Blinds. Jointly they perform the same function as a Spectacle Blind as essentially a simplistic valve. The Spade or Spacer is fitted in the line between two flanges and is bolted in place.
United Steelex FZE
Petrochemical Project Support Service
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