1、 105 Decker Court, Suite 825, Irving, TX 75062 P: 469-499-1044 F: 469-499-1062 www.plasticpipe.org Bolt Torque For Polyethylene Flanged Joints TN-38/July 2011 LAP-JOINT STYLE FLANGE ASSEMBLY (Based on ASME B16.5) 24-Inch Dia. Polyethylene Flange Adapters, Metal Lap-Joint Flanges, and Bolt Set 2 Fore
2、word This technical note was developed and published with the technical help and financial support of the members of the Plastics Pipe Institute. The members have shown their interest in quality products by assisting independent standard-making and user organizations in the development of standards,
3、 and also by developing reports on an industry-wide basis to help engineers, code officials, specifying groups, and users. The Plastics Pipe Institute, Inc. has prepared this technical note as a service to the industry. The information in this note is offered in good faith and believed to be accurat
4、e at the time of its preparation, but is offered without any warranty, express or implied. Additional information may be needed in some areas, especially with regard to unusual or special applications. Consult the manufacturer or material supplier for more detailed information. A list of member manu
5、facturers is available from PPI. PPI does not endorse the proprietary products or processes of any manufacturer, and assumes no responsibility for compliance with applicable laws and regulations. PPI intends to revise this report form time to time, in response to comments and suggestions from users
6、of this note. Please send suggestions for improvements to PPI. Information on other publications can be obtained by contacting PPI directly or visiting the web site. The Plastics Pipe Institute, Inc. 469-499-1044 www.plasticpipe.org 3 DISCLAIMER Due to the wide variation in service conditions, quali
7、ty of installations, etc, no warranty or guarantee, expressed or implied, is offered nor given in conjunction with the use of this Plastic Pipe Institute Technical Note. All data and formulae and example values presented here-in should be independently verified and validated by the end-user, reader,
8、 designer, engineer, field installer, technician, etc, for a specific HDPE pipeline flange installation or project. CAUTION FLANGES IN NATURAL GAS PIPELINES Note: In jurisdictional installations any metallic pipeline components must be protected from corrosion as prescribed in US CFR Title 49, Part
9、192, Subpart I, sections 451-491. Furthermore, Part 195 Subpart H, sections 551-589 applies to steel pipelines used in the transport of Hazardous Liquids. 4 Index Page i. Preface 5 ii. Introduction 6 iii. CHECKLIST : Bolt Torque Spec the contoured cross-section is typically cast using molten ductile
10、-iron or stainless-steel. The LJF is typically in flat-face contact with the polyethylene flange adapter hub, and has a radius on the contact side of the LJF ID which mates with the fillet radius of the matching polyethylene flange-adapter (stub-end). The LJF slips over the pipe; is not welded to th
11、e pipe; is loose until bolted; and is free to rotate into bolt-hole alignment with another flange. The bolt-load is transferred to the sealing face by the pressure of the LJF against the back-face of the HDPE hub. Two methods are commonly used to seal polyethylene Lap Joint Flange assemblies between
12、 various combinations of pipe materials such as HDPE to HDPE; HDPE to Steel; HDPE to Ductile-Iron; HDPE to PVC; HDPE to Fiberglass. The first method, (non gasketed), uses the specified HDPE seating torque initially applied to the HDPE flange adapters, followed by a mandatory re-torque applied 4-hour
13、s to 24-hours after completion of the initial torque application The second method, (gasketed), uses a low gasket seating bolt torque, applied to a soft elastomeric gasket, for lower pressure applications (like landfill gas collection or use with torque-limited PVC or fiberglass flanges), followed b
14、y the mandatory re-torque 4 hours to 24-hours after the initial torque. PPI strongly recommends that each flanged joint be independently analyzed by the project engineer for sealing capacity when subjected to all expected operating and installation loads. By applying the higher initial seating torqu
15、e to seat the un-marred HDPE faces, without gaskets, the final residual bolt torque (RBT) at the HDPE sealing stress is sufficient to contain flow-stream pressure under operating conditions. As is discussed later, the mandatory re-torquing to the initial target torque after a 4 hour to 24 hour creep
16、-relaxation period is done to compensate for possible bolt-creep, nut embedment, and, gasket compression-set (if gaskets are used). Consult the individual HDPE flange manufacturers for their recommended protocol. Flange-Adapter Manufacturers should verify their flange assemblies are performance rate
17、d when used with a specific style or manufacturers LJF. LJF (lap-joint flange) manufacturers should verify the maximum allowable torque that can be applied to their product, and that their LJFs provide “disk” deformation in excess of the polyethylene flange-adapters expected service lifes visco-elas
18、tic creep deformation, at low residual compressive stress. CAUTION: When bolting to fiberglass, cast iron, PVC pipe flanges, or PVC flanged valves, the “brittle” flange typically bolts to a special HDPE full-face flange adapter using lower bolt torque. Hence a soft gasket is frequently also used wit
19、h “brittle” pipes. Over-tightening, misalignment, or uneven tightening can break brittle material flanges. Extreme care is advised. Refer to Appendix C, and consult with the sensitive, low-strain product manufacturer for its maximum torque limits, when bolting to “raised-face” HDPE flange adapters.
20、When gaskets 6 are to be considered, review Appendix C very carefully, to perform calculations using the seating stress, blow-out resistance, crush resistance, and other performance values obtained from the gasket manufacturer. This Tech-Note does not provide guidance on gasket selection; consult wi
21、th the gasket designer to discus the parameters outlined in Appendix C. Introduction: Lap-Joint Flanges (LJF) have been used for decades. The typical polyethylene flange adapter with loose LJF is also known as a Van-Stone Flange joint. The HDPE flanged joint assembly is an engineered pressure contai
22、nment connection subject to diverse forces. While simple in appearance, its design is complex due to the axial shear, radial dilation, disk-bending moments, residual interfacial sealing pressure, bolt-load versus bolt-torque, HDPE flange face creep-relaxation, LJF disc flexure, axial tension from th
23、ermal contraction of the pipe-line, some vibration, pressure-surge, pipe bending due to soil settlement, etc. The greatest contributors to flange leakage are insufficient torque, un-even torque, and flange misalignment. Written and correct bolt torque specifications and installation procedures will
24、eliminate these problems. The flange assembly design, and written assembly specifications, are controlled by the pipeline design-engineer or project engineer-of-record. The ideal flange-adapter joint should exhibit Compressibility, Resilience, and Creep-Resistance. The plastic flange-adapter face sh
25、ould be able to compress into any and all surface texture and imperfections of the mating flange. The plastic flange face should be sufficiently and elastically resilient to move with dynamic loadings to maintain seating stress. The flange-adapter face should exhibit sufficient creep-resistance so a
26、s not to permanently deform after bolt-up under varying load cycles of temperature and pressure. The “memory” of pipe-grade HDPE makes it an ideal flange face sealing surface. It becomes its own “gasket flange”, and seals well when un-marred and torqued to meet or exceed the HDPE seating stress. Whe
27、n properly torqued with a flexible LJF, the HDPE flange-adapter becomes self-gasketing. The LJF assembly is typically evaluated as a combined mechanical “spring” assembly. The torqued bolts are elastically stretched to initiate the sealing pre-load. The metal LJF (lap-joint flange) is elastically fl
28、exed (bent by the bolt-load) to maintain the pre-load and to transfer the load to the HDPE flange face. At small strains, the HDPE flange-face is elastically and visco-elastically deformed (axial compression and slight radial enlargement) so as to maintain pre-load sealing pressure on the flange-fac
29、e surface. The HDPE flange face compressibility is the measure of its ability to deflect and conform to the mating flange face. This compressibility compensates for flange surface irregularities such as minor nicks, non-parallelism, metal corrosion, and variation in surface roughness or grooving dep
30、th. The HDPE flange face also exhibits Memory / Recovery / Resiliency which are measures of the elasticity of the HDPE material to recover shape and to maintain its deformation sealing pressure under varying loads across broad temperature ranges. Although the HDPE is a visco-elastic material that sl
31、ightly creeps over time, at sufficient torque the flexure of the LJF and bolt stretch exceed the expected long-term compressive creep of the flange face, such that the residual sealing force exceeds the sum of the operating separation forces. In this way, the sealing pressure is maintained. The comb
32、ined “springs” of the stretched bolts, the flexed disc LJF, and the elastic component of the compressed flange-face, all serve to provide an elastic / visco-elastic, resilient “spring-seal” of the hydrostatically pressurized joint. The key element to an effective sealing HDPE flanged joint, is to to
33、rque the bolts to a sufficiently high value to stretch the bolts, so that the LJF is flexurally distorted, and the HDPE flange-face sufficiently and continuously compressed. The joint is at equilibrium, with the compressive sealing force distributed across the sealing face and equal in magnitude to
34、the pre-tension in the 7 bolts. The total bolt tension must be able to constrain the joint assembly against operating pressure, surge pressure, pipe-line axial thermal contraction, and pipe bending strain from soil settlement, and flange angular alignment; all with an applied safety factor. Figure 1
35、 The total possible force required from bolting torque should equal and exceed the sum of applicable separation forces: FTotal FPress+ FSurge+ FTherm.Contr.+ FPipe-Bend+ FFlng-Alignment + F% Variance Equation # 1 Caution: The component, Fpipe-bend(forces from pipe beam-bending), in the above equatio
36、n can sometimes exceed thermal contraction and hydraulic forces. HDPE flange joints are geometrically rigid assemblies, unlike the flexible HDPE pipe ring “hoop”. The rigid flanged joint cannot shed stress by ring deformation. Localized HDPE pipe beam-bending at a flanged joint due to soil settlemen
37、t, water buoyancy or wave action, pipe “snaking” above ground, etc, must be managed so as to isolate the flange from beam-bending strain. External installation measures to protect PE flange joints from beam-bending strain are necessary. While additional torque can maintain the pressure seal, bending
38、 strain across the HDPE flange adapter should be limited to prevent flange adapter fracture. NOTE: Appendix “A” provides the method for calculation and determination of specified bolt torque at the required seating stress. Proceed to Appendix “A” to perform the required engineering calculations to d
39、etermine the required target torque to be used in the Checklist following on the next page. 8 CHECKLIST and FLANGE TORQUE RECORD: Project: _ Flange Set Location : _ Connecting HDPE Flange to _ Flange. Bolt Dia AWWA C110 It does not volumetrically compress. The hardness of HDPE is about 65 Shore D, s
40、lightly harder than some rubber, or Teflon gaskets. The thick face of the HDPE 16 flange adapter enables the user to compress the flange face, through bolt torque, such that the flange face is elastically compressed. For example, a 5% squeeze on a 1” thick flange face is about 0.050”. For a 3.5” thi
41、ck flange-face, the elastic compression strain is 0.175-inches. This strain is the approximate thickness of a traditional elastic, resilient, reinforced rubber gasket. As the HDPE thermally strains, the flange face compression compensates for the thermal strain and maintains an elastic sealing stres
42、s greater than the operating pressure. Hence un-damaged HDPE flanges remain sealed without gaskets. The HDPE flange face is a compliant sealing material at less than 8% compressive strain. NOTE: Some users specify sealing gaskets, based on their experience with metal flanges, but gaskets are not nec
43、essarily required for HDPE flanges at temperatures less than 140 F when the LJF is properly aligned, torqued, and the flange-adapter face is un-damaged. However, when the pipeline designer actually specifies gaskets, full-face gaskets are recommended, not the smaller ring-gaskets, as the full-face g
44、asket bolt-holes provide for proper centering and alignment during flange-joint assembly. Gasket diameters should match the HDPE flange face OD and ” or larger for 14” to 54” IPS sizes. The fusion-end wall-thickness is nominally 10% thicker than the pipe-wall to which it will be fused, to compensate
45、 partially for pipe toe-in (in addition to “facing back” most of the pipe toe-in); and to provide the potential for 100% pipe-wall fusion-contact. The HDPE flange adapter is normally rated at the same working pressure rating (WPR) as the nominal wall thickness pipe to which it will be fused. The nec
46、k of the flange adapter is sufficiently long so as to fit in a fusion machine and provide for fusion joining twice. Stub-end flanges may require a “holder” for use in the fusion machine. This technical note applies equally to serrated face and flat face HDPE flange adapters, when the minimum seating
47、 stress is met or exceeded, and when used with or without gaskets. Testing of the self-gasketing properties of HDPE was done at temperatures less than 100F. Flange adapter manufacturers have internal standards regarding flange face flatness, parallelism between the seal face and the LJF back-face, s
48、eal face angular alignment to the theoretical bore centerline, etc. If questions arise regarding such technical issues, then the flange adapter manufacturer should be consulted. THE METAL LAP-JOINT FLANGE: Lap-Joint Flanges can be cut from carbon steel plate, radiused, and drilled to the required bo
49、lt-hole pattern. The metallic, contoured cross-section LJF is cast from ductile-iron or stainless steel. The cast Ductile-Iron is normally ASTM A536 Grade 65-45-12. The cast Stainless Steel is normally ASTM 351 Grade CF8M (#316 stainless). The LJF OD, bolt-hole diameter, and bolt-circle dimensions conform to the ANSI /ASME B16.5 Class 150 dimensional patterns and specifications for diameters 3/4” thru 24” nominal pipe sizes (IPS AWWA C207 - CL 150 / B, D The Heavy Hex Head b
