1、Recommended DesignFactors and DesignCoefficients forThermoplastic Pressure PipeTR-9/20021825 Connecticut Ave., NW Suite 680 Washington, DC 20009P: 202-462-9607F: 202-462-9779www.plasticpipe.org2FOREWORDThis report was developed and published with the technical help and financial support ofthe member
2、s of the PPI (Plastics Pipe Institute, Inc.). The members have shown theirinterest in quality products by assisting independent standards-making and userorganizations in the development of standards, and also by developing reports on anindustry-wide basis to help engineers, code officials, specifyin
3、g groups, and users.The purpose of this technical report is to provide important information available to PPIon design factors and design coefficients recommended for thermoplastic pressurepiping applications. These recommendations are based on discussions with severalinternationally recognized tech
4、nical experts in the plastic pipe industry. More detailedinformation on its purpose and use is provided in the document itself.This report has been prepared by PPI as a service of the industry. The information inthis report is offered in good faith and believed to be accurate at the time of itsprepa
5、ration, but is offered without any warranty, expressed or implied, includingWARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULARPURPOSE. Any reference to or testing of a particular proprietary product should not beconstrued as an endorsement by PPI, which do not endorse the proprietary product
6、s orprocesses of any manufacturer. The information in this report is offered forconsideration by industry members in fulfilling their own compliance responsibilities. PPIassumes no responsibility for compliance with applicable laws and regulations.PPI intends to revise this report from time to time,
7、 in response to comments andsuggestions from users of the report. Please send suggestions of improvements to theaddress below. Information on other publications can be obtained by contacting PPIdirectly or visiting the web site.The Plastics Pipe InstituteToll Free: (888) 314-6774http:/www.plasticpip
8、e.orgOctober 20023Recommended Design Factors and Design Coefficients forThermoplastic Pressure Pipe1.0 GENERAL INTRODUCTIONThis Technical Report provides a summary of industry recommended design factors(DF) used with the Hydrostatic Design Basis (HDB) determined in accordance withASTM D 2837, and re
9、commended design coefficients (C) used with the MinimumRequired Strength (MRS) determined in accordance with ISO 9080 and ISO 12162. Toavoid confusion, we are using the standard definitions and terms in this report that arerecognized internationally in ASTM and ISO documents.These design factors and
10、 design coefficients differ because of the conventions by whichHDB and MRS are determined. Therefore, one should not use a design factor (DF) withMRS or a design coefficient (C) with HDB.Other PPI Technical Reports that are concerned with pressure applications ofthermoplastic pipe material are PPI T
11、R-4, “PPI Listing of HDB, SDB, PDB and MRSRatings for Thermoplastic Piping Materials or Pipe“, and PPI TR-3, “Policies andProcedures for Developing HDB, PDB, SDB and MRS Ratings for Thermoplastic PipingMaterials or Pipe“.These recommended design factors and design coefficients have been developed on
12、the basis of several years of international field experience, engineering tests,investigations, and safety considerations. Experience to date indicates that they areconservative within the limits for which they are recommended. However, no guaranteeor warranty can be assumed regarding their applicat
13、ion and use. Under someconditions, such as cyclic pressure applications or applications where theconsequences of failure are heightened, a more conservative (i.e., smaller DF or largerC) should be applied.2.0 STANDARD TERMINOLOGY2.1 HDB MethodLong-Term Hydrostatic Strength (LTHS) - the hoop stress t
14、hatwhen appliedcontinuously, will cause failure of the pipe at 100,000 hours (11.43 years). This is theintercept of the stress regression line with the 100,000-h coordinate as defined in ASTMD 2837. Note The typical condition uses water as the pressurizing fluid at 23C (73F).Hydrostatic Design Basis
15、 (HDB) one of a series of established stress valuesspecified in Test Method D 2837 “Standard Test Method for Obtaining HydrostaticDesign Basis for Thermoplastic Pipe Materials” for a plastic compound obtained bycategorizing the LTHS determined in accordance with Test Method D 2837. HDB refersto the
16、categorized LTHS in the circumferential, or hoop direction, for a given set of end4use conditions. Established HDBs are listed in PPI TR-4.Design Factor (DF) - a number less than 1.00 that takes into consideration thevariables and degree of safety involved in a properly installed thermoplastic press
17、urepiping installation. For purposes of this document, a service design factorrecommended for use with an HDB category is designated DFS. Hydrostatic Design Stress (HDS) the estimated maximum tensile stress (psi) in thewall of the pipe in the circumferential orientation due to internal hydrostatic p
18、ressure thatcan be continuously applied with a high degree of certainty that failure of the pipe willnot occur.HDS = HDB X DFHDB Pressure Rating (PRHDB) - the estimated maximum pressure (psig) that themedium in the pipe can exert continuously with a high degree of certainty that failure ofthe pipe w
19、ill not occur.PRHDB= 2 (HDB) (DF) = 2 (HDS)DR-1 DR -12.2 MRS MethodLower Predictive Limit (LPL) a pipe materials 97.5% lower confidence level of theextrapolated value (typically at 20C and 50 years) obtained in accordance with ISO9080 “Determination of the long-term hydrostatic strength of thermopla
20、stics materials inpipe form by extrapolation”.Minimum Required Strength (MRS) - the categorized lower predictive limit (LPL) ofthe ISO 9080 long-term strength at 20C and 50 years as defined in ISO 12162,“Thermoplastic materials for pipes and fittings for pressure applications Classificationand desig
21、nation Overall service (design) coefficient.Design Coefficient (C) - a number greater than 1.00 that takes into consideration thevariables and degree of safety involved in a properly installed thermoplastic pressurepiping installation. For purposes of this document, a service design coefficientrecom
22、mended for use with an MRS category is designated CS. Hydrostatic Design Stress (_HDS) the estimated maximum tensile stress (psi) in thewall of the pipe in the circumferential orientation due to internal hydrostatic pressure thatcan be continuously applied with a high degree of certainty that failur
23、e of the pipe willnot occur._HDS= MRSC5MRS Pressure Rating (PRMRS) - the estimated maximum pressure (bar) that themedium in the pipe can exert continuously with a high degree of certainty that failure ofthe pipe will not occur.PRMRS= 20 (MRS)(DR-1) C3.0 SIGNIFICANCEA design factor or design coeffici
24、ent is intended to make allowance for two generalgroups of conditions. The first group considers manufacturing and testing variables;specifically, normal variations in the material, manufacture, dimensions, and in theevaluation procedures (ASTM D 2837 and D 1598, for example). Experience to dateindi
25、cates that the variation due to this group of conditions is usually within plus or minusten percent. The second group considers installation, chemical environment (bothinside and outside the piping), temperature, hazard involved, life expectancy desired,and the degree of reliability selected If the
26、temperature of use and/or the chemicalenvironment differs from that associated with the long-term stress rating, an additionalchemical design factor (DFC) is used. If anticipated handling and installation proceduresmay adversely affect the material, the service design factor (or design coefficient)s
27、hould be reduced (increased) to account for these effects.4.0 THE HDB APPROACHA. Introduction to HDBThe Hydrostatic Design Basis (HDB) is the categorized long-term hydrostatic strength(LTHS) determined in accordance with ASTM D 2837. General ASTM thermoplasticpipe specifications use the HDB at 73F (
28、23C) to establish dimensions and maximumoperating pressures. PPI lists HDBs and maximum recommended HDSs for specificthermoplastic piping materials in TR-4. The service design factor used to obtain theseHDS values is 0.50, which is the service design factor for water.HDS = HDB X 0.5B. Service Design
29、 FactorProduct standards or codes for specific applications or jurisdictions may require moreconservative service design factors (DFS) reflecting additional design or safetyconsiderations. A governmental agency, a trade association or standards writing groupmay establish the service design factor. A
30、s an example, in the United States theDepartment of Transportation has assigned a service design factor of 0.32 for all plasticpipe used in natural gas applications. These regulations may result in requiring that anactual pressure rating being marked on the pipe (e.g., ASTM D 2241 and AWWA C6900) or
31、 it may require a pressure rating code letter be marked on the piping (e.g., ASTMD 2513).Some of the accepted industry maximum service design factors are given in Table 1.TABLE 1 - MAXIMUM RECOMMENDED SERVICEDESIGN FACTORS FOR USE WITH HDB-RATED MATERIALSSERVICEAPPLICATIONTHERMOPLASTIC PIPINGMATERIA
32、LMAXIMUM SERVICEDESIGN FACTOR for HDBDFSWater PE and other approved materials 0.50PVC distribution pipe 0.40PVC transmission pipe 0.50Fuel GasDistribution(USA)All approved materials 0.32Fuel GasDistribution(Canada)All approved materials 0.40Dry natural gas All approved materials 0.50C. Temperature E
33、ffectPPI publishes HDB values in TR-4 at 73F (23C) and also at other selected elevatedtemperatures (120F, 140F, etc.). Where recommended by the manufacturer, the HDBat this elevated temperature is used with the appropriate service design factor andwithout the need for a temperature design factor. Th
34、is is the preferred method toaccount for elevated temperature because it is more accurate.HDS(140F)= HDB(140F) (DFS)For service temperatures between 73F and the elevated temperature at which the pipemanufacturer has established an HDB,the user may arithmetically interpolate the HDBat his service tem
35、perature (T) to determine the appropriate pressure rating:HDS(T)= HDB (interpolated between two temperatures) (DFS)7PPI has published a temperature interpolation policy in TN-18, “Long-Term Strength(LTHS) By Temperature Interpolation”. This policy is also included in TR-3.If the service temperature
36、exceeds the maximum established HDB for a material, themanufacturer should be consulted to obtain an appropriate recommended temperaturedesign factor (DFT):HDST= HDB(73F) (DFS) (DFT)Where a recommendation is not available from the manufacturer, conservative values,such as those in Table 2 for PVC, m
37、ay be used. These PVC values for DFTareconsistent with AWWA C900 and C905. Temperature design factors should only beused when an established HDB is not available at the desired temperature.TABLE 2 - Maximum Recommended TEMPERATURE DESIGN FACTORSService Temperature(F)Service Temperature(C)Temperature
38、 DesignFactor (DFT)For PVC80 27 0.8890 32 0.75100 38 0.62120 49 0.40130 55 0.30140 60 0.22With liquid hydrocarbons and other chemicals, temperature can have a disproportionaleffect on the long-term performance of the pipe. No general chemical design factor forelevated temperature service can be esta
39、blished and each case should be designed onits own merit.D. Chemical EffectsBecause of the wide differences in chemical resistance of various thermoplastic pipingmaterials, specific attention should be given to the effect of the transported medium fluidon the piping. Experience has shown that the ef
40、fects of air, water, natural gas, andneutral salt solutions on the long-term stress rating are relatively insignificant withpresently used thermoplastic pressure piping materials. However, other fluids mayhave a significant effect on the long-term strength of thermoplastics pipe materials. Thedesign
41、 engineer must consider these effects. In these cases, use of a chemical designfactor (DFC) is appropriate. Table 3 gives, as an example, maximum recommendedchemical design factors for three thermoplastic materials when continuously exposed to8liquid hydrocarbons.Table 3 - Maximum Recommended Chemic
42、al Design Factors forContinuous Liquid Hydrocarbon ExposurePipe Material Chemical Design Factor(DFC)PA polyamide 1.00PE polyethylene 0.50PVC poly (vinyl chloride) 0.50E. Overall Design Factor/Pressure RatingMultiple design factors (service, temperature, chemical, others) may be necessary forcertain
43、applications. For example, one may apply a service design factor (DFS) for aspecific application and a temperature design factor (DFT). One could also apply achemical design factor (DFC) if that piping is used in the presence of a chemicalenvironment that lowers the long-term stress capacity of the
44、material (see PPI TR-19and TR-22). The overall design factor (DF) is the product of all these design factors:DF = (DFS) (DFT) (DFC)Pressure ratings (PR) are calculated from the dimension ratio of the pipe (DR), thematerials hydrostatic design basis (HDB), and the overall design factor (DF):PR (psig)
45、 = 2 (HDB) (DF)(DR - 1)95.0 THE MRS APPROACHA. Introduction to MRSThe Minimum Required Strength (MRS) is the categorized long-term hydrostaticstrength determined in accordance with ISO 9080 and ISO 12162. PPI lists MRSs forspecific thermoplastic piping materials in TR-4. For classification purposes,
46、 the MRS isobtained at 20C and 50 years. For pressure rating calculations, the MRS may beobtained at the desired use temperature and the desired time.B. Design CoefficientThe standard ISO 12162 describes the “overall service (design) coefficient“ or “C-factor“and details the contents of this coeffic
47、ient and gives the minimum values to be used forthis coefficient. The minimum coefficient is established for static water pressure at20 C for 50 years, and takes into account the following considerations:1. Additional stress and other unquantifiable effects which are considered to arise inthe applic
48、ation;2. Influence of temperature, time and environment inside or outside of the pipe, ifdifferent from 20 C, 50 year and water. This influence can have either positive ornegative effects;3. Standards relating to MRS for temperatures other than 20 C.The C coefficient is related to the pipe material
49、and the anticipated installation andoperating conditions. It should be corrected with individual factors introduced toseparately cover material and application aspects. The material related coefficient (CM)reflects the properties of the components of a piping system other than thoserepresented in the lpl(e.g. extrusion, batch to batch variation).The application related coefficient (CA) is left to the design engineer to incorporate viaappropriate design codes (e.g. ISO 10839) and national regulations and should bedepend
