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Form Tolerances Bending

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153 views7 pages

Form Tolerances Bending

Uploaded by

Quang2 Nguyen
Copyright
© © All Rights Reserved
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PFI Standarl ES-24 (Revised 1982) Pipe Bending Methods, Tolerances, Process and Material Requirements Prepared by Engineering Commitee ‘Ai PF Snares ao senor only Thera is no agree. ‘Mon to achere fo ay PPI Stenoac and mei se by ‘Tiyowe enti voluntary. Copyright By Pipe Fabrication Institute P.O. Box 173 © Springdale, PA 15144 Dedicated to Technical Advancements and Standardization in the Pipe Fabrication Industry since 1913 1.0 SCOPE 4.1 This standard covers methods, process require- ments, tolerances and acceptance criteria for shop fabricated pipe bends. 1.2 The bending methods described in this standard are a partial representation of commonly used processes and do not preclude the use of other methods. 2.0 TERMINOLOGY 2.4 The symbols and terms defined below are used throughout this standard: ENTER TO END -+j oe cei ee oes S| —- 5 FIGURE 2.1 1D = Nominal pipe size. Dn = Nominal outside diameter of pipe. th = Nominal wall thickness of pipes. tm = Minimum calculated wail thickness required by the applicable code. T= Pipe wall thickness (measured or minimurn, in accor- dance with purchase specifiction). = Center line radius of bend. 3.0 BENDING METHODS 3.1 This standard covers bends formed by both hot and cold bending methods. For this standard, a temperature 100 degrees F below the lower criti- cal temperature of the material is defined as being the boundary between hot and cold bending. 3.2 Unless otherwise specified by the governing code, the bending procedure, including the heating/coo!- ing cycle and post bend neat treatment, is deter mined by the pipe material, diameter, wall thickness, bend radius and the required proper: ties after bending. Because of the many variables involved, the bending procedure should be deter- mined by the fabricator. 3. While the bending equipment used in many of the methods is generically the same, there may be differences in bending procedures, material allowances, hold and pull legs, wall thickness, etc, between bending fabricators. 34 HOT BENDING METHODS 3.4.1 FURNACE BENDING: In this method, the pipe is firmly packed with ‘sand and then heated in a furnace to a tem perature in the range of 2000 degrees F. After removing from the furnace, one end of the pipe is retained in a holding device and a bending moment is applied at the other end. The radius of the bend is controlled by dies, stops or tempiates as the pipe is bent. For long radius bends andlor heavy wall pipe, the sand filling operation may not be necessary. 7 pablus sToPS— JS (OPTIONAL PULLING DEVICE FIGURE 344 FURNACE BENDING 4.2 INCREMENTAL BENDING: ‘The incremental bending equipment is com- posed of an anchor box, a hydraulic cylin- der, and @ moveable heating device. The pipe is clamped in the anchor box and the front tangent is connected to the hydraulic cylinder. The heating device heats a narrow circumferential band on the arc to the proper bending temperature. A force is then applied by the hydraulic cylinder to bend the small increment a predetermined amount. The heating device is then moved to successive segments where the process is repeated until the required arcs altained. Alter bend- ing each increment, the heated area is cooled as required by the appropriate bend- ing procedure. sc Hens oE vice f © snciion sox HYORAULIG CYLINDER = FIGURE 34.2 INCREMENTAL SENDING ai 343 INDUCTION BENDING: ‘The induction bending equipment is com- posed of three Basie components consisting ot a bed, a racial arm, which is set at the ! required radius, and an incueion heating @ system. The pipe is piaced in the bed and : the front tangent is clamped to the racial atm. The induction heating system hoais a ; narrow circumferential band around he pipe 10 the appropriate bonding temperature, When this temperature is reached, he pipe is continvously moved through tne heating coil while a bending moment is applied to the heated area. Alto passing through the coil, the pipe may be elther forced or natu rally Cooled 2s required by the appropiate Qualified bonding procedure. piNouerion con, QO. ; oO Y ( RADIAL : hf ant FIGURE 243 x INDUCTION BENDING @ 25 cov sewoIne erHoos 85.1 ROTARY DRAW BENDING: In this method, the pipe is secured to a bend- ing die by a clamping die. As the bending die rotates, it draws the pipe against the pressure die and, if necessary to prevent wall collapse, over an internal mandrel. The pressure die may remain fixed or move with the pipe. PRESSURE OIE ROTATING BEND DIE — : FIGURE 35.1 ROTARY DRAW BENDING 35.2 RAM BENDING: In ram bending, the pipe is held by two sup- porting dies and a force is applied by means of a hydraulic ram to a forming shoe located al the center of the workpiece. The support ing dies rotate on their mounting pins so that they follow the pipe and maintain external support throughout the operation. —supront HyORAULIC RAM 7 oe Formine sxe FIGURE 35.2 RAM BENDING 383 ROLL BENDING: . In roll bending, three forming rolls of approx: imately the same diameter arranged in a pyramid are used. The two fixed rolls oppose the adjustable center roll. The pipe Is passed through the rolls with the position of the adjustable roll controlling the bend radius. FIGURE 353 ROLL BENDING. 4.0 WELDS IN BENDS 4.1 In some instances it Is not practical to utilize pipe of sufficient lengih to satisty the required ‘arc length of the bend. When it becomes neces- sary to join lengths of pipe resulting in a circum- ferential butt weld in the arc of a pipe bend, the following practices should be considered: 4.141 Pipes to be welded should be selected to pro- vide the best uniformity possible at the mating ends. Pipe wall thickness shall not be less than. the design minimum plus bend thinning allow- ance (see seclion 7.0). 4.4.2 End preparation for welding shall be in accord ance with the qualified wetding procedure to be used. Internal counterboring should be a- voided wherever possible. During fit-up of the joint, the pipes should be rotated or aligned 28 necessary to provide the leasi amount of LD. and/or 0.0. mismatch and the best tram ition across the weld. 4.1.3 The welding procedure must be qualified in ac- cordance with the governing Code for the ther- ‘mal exposures, {if any) excepted in bending and heat treatment, 4.14 Aller completion of the circumferential bult weld, but before bending, the 0.0, and LD. (where accessible) of the weld should be Ground to remove excess weld reinforcement and blended smoothly into the base metal. 4.4.5 It is" good practice to examine the circumfer ential butt weld by radiography prior to and after bending, whether or not such radiography is required by the applicable Code. 5.0 LINEAR AND ANGULAR TOLERANCES 5.1 Bends shall-be-provided-with_a total angularity tolerance of + 5 degrees as delermined by the ‘

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