1、PFI Standard ES-24 |Denotes Revision (Revised December 2013) PIPE BENDING METHODS, TOLERANCES, PROCESS AND MATERIAL REQUIREMENTS Prepared by Pipe Fabrication Institute Engineering Committee All PFI Standards are advisory only. There is no agreement to adhere to any PFI Standard and their use by anyo
2、ne is entirely voluntary. Copyright by PIPE FABRICATION INSTITUTE Dedicated to Technical Advancements and Standardization in the Pipe Fabrication Industry Since 1913 USA 511 Avenue of Americas, # 601 New York, NY 10011 CANADA 655, 32ndAvenue, # 201 Lachine, QC H8T 3G6 WEB SITE www.pfi-institute.orgP
3、FI Standard ES-24 |Denotes Revision (Revised December 2013) Pipe Bending Methods, Tolerances, Process and Material Requirement METRIC CONVERSIONS The conversion of quantities between systems of units involves a determination of the number of significant digits to be retained. All conversions depend
4、upon the intended precision of the original quantity and are rounded to the appropriate accuracy. Pipe sizes together with applicable wall thicknesses are not shown with metric equivalents. The SI (metric) values where included with the customary U.S. values in this Standard are the rounded equivale
5、nts of the U.S. values and are for reference only. Metric units were derived utilizing the following conversion factor: Conversion Factor Conversion Factor Inches to 25.4 Deg. Fahr. to 5/9 (Deg. F. 32) Mitlimeters Deg. Cent. Lb/in2to 0.0703 Kg/cm21. Scope 1.1 This standard covers methods, process re
6、quirements, 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. Terminology 2.1 The symbols and terms defined below are used thro
7、ughout this standard: TANGENTTANGENTRDnBEND EXTRADOSBEND INTRADOSFIGURE 2.1 D = Nominal pipe size. Dn = Nominal outside diameter of pipe. tn = Nominal wall thickness of pipes. tm = Minimum calculated wall thickness required by the applicable code. T = Pipe wall thickness (measured or minimum, in acc
8、ordance with purchase specification). R = Center line radius of bend. 3. 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 critical temperature of the material is defined as being the boundary be
9、tween hot and cold bending. 3.2 Unless otherwise specified by the governing code, the bending procedure, including the heating/cooling cycle and post bend heat treatment, is determined by the pipe material, diameter, wall thickness, bend radius and the required properties after bending. Because of t
10、he many variables involved, the bending procedure should be determined by the fabricator. PFI Standard ES-24 |Denotes Revision (Revised December 2013) 3.3 While the bending equipment used in many of the methods is generically the same, there may be differences in bending procedures, material allowan
11、ces, hold and pull legs, wall thickness, etc., between bending fabricators. 3.4 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 temperature in the range of 2000 degrees F. After removing from the furnace, one end of the
12、 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 templates as the pipe is bent. For long radius bends and/or heavy wall pipe, the sand filling operation may not be necessary. HOLDING SHOESRADIUS STOPS(OPTIO
13、NAL)PULLING DEVICE FIGURE 3.4.1 FURNACE BENDING 3.4.2 INCREMENTAL BENDING: The incremental bending equipment is composed of an anchor box, a hydraulic cylinder, and a moveable heating device. The pipe is clamped in the anchor box and the front tangent is connected to the hydraulic cylinder. The heat
14、ing 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
15、arc is attained. After bending each increment, the heated area is cooled as required by the appropriate bending procedure. ANCHOR BOXHEATING DEVICEHYDRAULIC CYLINDERFIGURE 3.4.2 INCREMENTAL BENDING 3.4.3 INDUCTION BENDING: The induction bending equipment is composed of three basic components consist
16、ing of a bed, a radial arm, which is set at the required radius, and an induction heating system. The pipe is placed in the bed and the front tangent is clamped to the radial arm. The induction heating system heats a narrow circumferential band around the pipe to the appropriate bending temperature.
17、 When this temperature is reached, the pipe is continuously moved through the heating coil while a bending moment is applied to the heated area. After passing through the coil, the pipe may be either forced or naturally cooled as required by the appropriate qualified bending procedure. BEDRADIALARMI
18、NDUCTION COILFIGURE 3.4.3 INDUCTION BENDING PFI Standard ES-24 |Denotes Revision (Revised December 2013) 3.5 Cold bending methods 3.5.1 ROTARY DRAW BENDING: In this method, the pipe is secured to a bending die by a clamping die. As the bending die rotates, it draws the pipe against the pressure die
19、and, if necessary to prevent wall collapse, over an internal mandrel. The pressure die may remain fixed or move with the pipe. ROTATING BEND DIEPRESSURE DIECLAMPFIGURE 3.5.1 ROTARY DRAW BENDING 3.5.2 RAM BENDING: In ram bending, the pipe is held by two supporting dies and a force is applied by means
20、 of a hydraulic ram to a forming shoe located at the center of the workpiece. The supporting dies rotate on their mounting pins so that they follow the pipe and maintain external support throughout the operation. HYDRAULIC RAMFORMING SHOESUPPORTDIEFIGURE 3.5.2 RAM BENDING 3.5.3 ROLL BENDING: In roll
21、 bending, three forming rolls of approximately 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 3.5.3 ROLL BENDING 4. Welds in Ben
22、ds 4.1 In some instances it is not practical to utilize pipe of sufficient length to satisfy the required arc length of the bend. When it becomes necessary to join lengths of pipe resulting in a circumferential butt weld in the arc of a pipe bend, the following practices should be considered: 4.1.1
23、Pipes to be welded should be selected to provide the best uniformity possible at the mating ends. Pipe wall thickness shall not be less than the design minimum plus bend thinning allowance (see section 7.0). 4.1.2 End preparation for welding shall be in accordance with the qualified welding procedur
24、e to be used. Internal counterboring should be avoided wherever possible. During fit-up of the joint, the pipes should be rotated or aligned as necessary to provide the least amount of I.D. and/or O.D. mismatch and the best transition across the weld. 4.1.3 The welding procedure must be qualified in
25、 accordance with the governing Code for the thermal exposures, (if any) excepted in bending and heat treatment. 4.1.4 After completion of the circumferential butt weld, but before bending, the O.D. and I.D. (where accessible) of the weld should be ground to remove excess weld reinforcement and blend
26、ed smoothly into the base metal. 4.1.5 It is good practice to examine the circumferential butt weld by radiography prior to and after bending, whether or not such radiography is required by the applicable Code.PFI Standard ES-24 |Denotes Revision (Revised December 2013) 5. Linear and Angular Toleran
27、ces 5.1 Bends shall be provided with a total angularity tolerance of .5 degrees as determined by the intersection of the tangent centerlines measured by appropriate equipment. 5.2 When the fabricator is required to provide bends cut to a specified center-to-end dimension it shall be to the tolerance
28、s specified in PFI ES-3. 5.3 If intermediate portions of the bend profile are essential, their tolerances shall be a matter of agreement between the purchaser and the fabricator. 5.4 See fig. 9.3 for an explanation of terminology regarding bend tolerances. 6. Form Tolerances 6.1 The ovality of a pip
29、e bend shall not exceed the ovality required by the governing code. If there is no governing code, the difference between the maximum and minimum diameters shall not exceed 8% of the average measured outside diameter of the straight portion of the pipe unless by mutual agreement between the purchase
30、r and the fabricator. Where operating conditions require less ovality it may be necessary to use larger radii, heavier pipe walls or a specific bending method that will provide a closer control of ovality. 6.2 Since there are occasions when buckles cannot be avoided, the following restrictions shoul
31、d apply: (a) All wave shapes shall blend into the pipe surface in a gradual manner. (b) The maximum vertical height of any wave, measured from the average height of two adjoining crests to the valley, shall not exceed 3% of the nominal pipe size. (See Figure 6.2, Note 1) (c) The minimum ratio of the
32、 distance between crests as compared to the height between crests and the included valley should be 12 to 1. (See Figure 6.2, Note 2) A123FIGURE 6.2 APPLICATION OF PIPE WALL BUCKLING TOLERANCES Note 1 Depth of average crest to valley is the sum of the outside diameters of the two adjoining crests di
33、vided by two, minus the outside diameter of the valley. DepthOD ODOD()()()1322Note 2 Ratio of distance between crests to depth is: ADepth (per Note 1)1216.3 Buckles which exceed the above tolerances will be subjected to corrective action to bring them within tolerance. 6.4 If operating conditions re
34、quire tighter tolerances on buckles, it may be necessary to use larger radii, heavier pipe walls or a specific bending process. 6.5 To determine what bends can be produced with a satisfactory degree of quality, the Pipe Fabrication Institute has conducted studies on carbon steel and low alloy steel
35、hot bends to determine minimum recommended bend radii for various ratios of outside diameters to wall thickness. The resulting bending range determined by these studies for each of the bending processes is shown in Figure 6.5.1 and 6.5.2. PFI Standard ES-24 |Denotes Revision (Revised December 2013)
36、3412506720010 3040506070FIGURE 6.5.1 FURNACE BENDING RANGE 25 50 10075 125 150034125067FIGURE 6.5.2 INDUCTION AND INCREMENTAL BENDING RANGE 6.6 Two examples are given for the determination of minimum recommended wall thickness and bending radius combinations for a given pipe size. Example A: Determi
37、ne minimum permissible bending radius required for furnace bending 12“-Extra Strong carbon steel pipe per ASTM A 106-Grade B. (1) Determine the diameter to wall thickness ratio. 12“ X-Stg. is 12.75“ O.D. with a .500“ nominal wall. Under ASTM A 106, the minimum wall is .438“. Therefore Dn/T = 12.75/.
38、438 = 29.l. (2) Enter 29.1 on the Dn/T axis of Figure 6.5.1 and move vertically to the intersection with the bending range boundary. (3) Then move horizontally to determine the minimum recommended radius to diameter ratio which equals approximately 4.5. For practical purposes, bending radii are seld
39、om expressed in terms of fractional numbers, but rather in terms of whole integers multiplied by the nominal pipe size. Hence, the recommended bending radius would be 5 x 12 = 60“. Example B: Determine the minimum permissible wall thickness required for induction bending 22“ O.D. carbon steel pipe p
40、er ASTM A 53-Grade B at a 3D bend radius. (1) Enter 3 on the R/Dn axis of figure 6.5.2 and move horizontally to the intersection with the bending range boundary. (2) Then move verticality to determine the minimum recommended diameter to wall thickness ratio which equals approximately 45. i.e. Dn/tn
41、= 45 or tn = Dn/45 = 22/45 = .489“. 6.7 Figure 6.5.1 is based on extensive experience in furnace bending carbon and low alloy steel pipe. Since stainless and non-ferrous materials have higher coefficients of expansion than carbon and low alloy steels, a greater reduction in the density of the sand f
42、ill occurs as these materials are being heated to the bending temperature. As a result, the sand fill does not provide the same rigidity against flattening and buckling as it does when carbon or low alloy steel pipe is being bent. Because of this fundamental difference, special consideration must be
43、 given to the selection of the minimum bending radius by the design engineer. 6.8 Cold bending ranges can vary significantly with the process and degree of specialized tool used. Figure 6.8.1 can be used to select the type of bend or the process required. PFI Standard ES-24 |Denotes Revision (Revise
44、d December 2013) 0 25 50 75 100 125 1501211109876543210WITHMANDRELRAMA complete list of PFI members and available membership CHARTER MEMBERS CONTRACTOR MEMBERS ASSOCIATE MEMBERS AFFILIATE MEMBERS HONORARY MEMBERS Associate and Affiliate member contributors Walter Sperko Sperko Engineering Services,
45、Inc. Greensboro, NC Thomas Warrelmann Victaulic Company of America Easton, PA Sheryl Michalak Welding Outlets, Inc. Houston, TX PFI Standards and Technical Bulletins are published to serve proven needs of the pipe fabricating industry at the design level and in actual shop operations. Hence, such ne
46、eds are continually considered and reviewed by the Engineering Committee of the Pipe Fabrication Institute to provide recommended procedures, which have been demonstrated by collective experiences to fulfill requirements in a manner for Code compliance. However, as the PFI Standards are for minimum requirements the designer or fabricator always has the option of specifying supplementary conditions in the form of requirements beyond the scope of the PFI publications.
