Design Guide: Supporting FRP Piping Systems

Britt Engineering Associates, Inc.Birmingham, ALexcess of support ratings will require specialdesigns and should be brought to theattention of Britt Engineering Associates7. SUPPORTS for INSULATED PIPE Special supports are used to accommodateup to 4" of insulation. In all except veryspecial cases the supports, anchors, andguides are attached to the pipe and are notdesigned to clamp or support the outside ofthe insulation. When heat tracing is requiredthe tracing passes outside of the support. ***Important *** If heat tracing is requiredcontact Britt Engineering Associates forspecial details and designs.8. COMPONENT SUPPORTS - It is veryimportant that all valves and inlinecomponents be supported independently ofthe pipe. In some instances, it is necessaryto anchor the component where heavyactuators are cantilevered off of the valve orcomponent or where external loads ordynamics might damage the pipe.Components in vertical and horizontal piperuns require support although components invertical runs may not require independentsupport of each component,9. EXPANSION - The thermal expansionof FRP is two times that of steel andrequires special attention especially where afully anchored system is not used.Expansion joints and expansion loops aresometimes specified, but these add a1-27-2018Page 5 of 16weakness to the system. Expansion loops inaddition to adding extra piping will add asmany as four fittings and at least eight morejoints. Each joint is an additional point ofweakness. If lack of structural restraintpresents a problem where anchor loadsmight preclude the use of the anchoredsystem, there are several other designmethods that can be employed, but in mostcases, the anchored system can beincorporated. The description of the otherdesign methods is beyond the scope of thismanual because these are special cases. Ifthere is a problem in using the anchoredtechnique call Britt Engineering Associatesand we will be glad to discuss specificapplications.10. COATINGS – Hot dip galvanizes is themost common finish but a high-qualityprime coat that is applied by spray coating isavailable. Paint systems are in compliancewith EPA regulations regarding VOC andhazardous materials. It is very importantthat the designer selects a corrosion resistantcoating that will withstand theenvironmental conditions in the area wherethe pipe supports are to be installed. Ifspecial high-performance coatings arerequired these should be specified in thepurchase documents. Britt EngineeringAssociates is able to provide any coatingsystem that might be required and can alsoprovide assistance in the selection of specialcoatings.Britt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, ALDesign Considerations for FRP Piping SystemsBackground - The use of fiberglassreinforced plastic (FRP) in the constructionof pipe for process piping systems isbecoming more and more popular. Thepossibilities of its utilization in new andunique ways have outgrown the availablebody of knowledge necessary to assure itsproper application. The shared interestamong designers is to extend the range andquality of those and other new applications.There are many years of practical experiencein every area of FRP application, yet there islittle published data that would allow anengineer to establish basic ground rules forthe design of an FRP process piping system.Recently, there has been tremendous growthin the use of FRP in piping systems, and itappears that this growth will continue.The purpose of this report is to present thebasic principles that have been usedsuccessfully to design FRP piping systems1-27-2018Page 6 of 16and also to describe problem areas that havecaused difficulty. The main emphasis of thisreport is toward piping design rather thanmaterial selection. The task of materialselection has been much simplified throughthe efforts of resin suppliers who providecomplete corrosion data for the properselection of a resin system. Most resinsuppliers will also provide case historiesdetailing the behavior of their products inalmost every environment and application.Mechanical Properties - After the selectionof a resin system, a determination as to thetype of pipe must be made. There are threemajor categories of FRP pipe construction.They are: (1) contact molded, (2) filamentwound, and (3) centrifugally cast. Themechanical properties of the pipe are closelylinked to the method of fabrication, andthose properties vary considerably amongthe three types.Britt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, ALDespite conjecture as to the advantages anddisadvantages of each type of pipeconstruction, it has been found that any ofthe three can be utilized if the pipe is of highquality and if the system has been properlydesigned and supported. The specificmechanical properties of the pipe selectedare incorporated into the design of thesystem. This includes the location and typeof support. The mechanical propertiesinherent to the method of pipe fabricationare discussed in a later section.operational temperature range of the system.The catalogs for many pipe manufacturerslist the range of properties for variouslaminates, but very few provide performancedata at elevated temperatures. The equationwhich is used to determine the designaspects of any structural system utilizesfactors for the mechanical properties underthe expected design conditions, includingtemperature. Without this information, thedesigner is severely handicapped.The most important factor in the design of apiping system is the determination of themechanical properties of the pipe over the1-27-2018Page 7 of 16Britt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, AL1-27-2018Page 8 of 16Britt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, ALFigure 1 shows the change in modulus at elevated temperatures for two filament woundpolyester pipes. This type of data is required in system analysis if the design is to be soundComparisons - The following compares andcontrasts the design features and advantagesof the three types of FRP pipe:Contact Molded. The high resin to glassfiber ratio of this pipe makes it ideal forhighly corrosive fluids. In order to meet thestrength requirements in the hoop direction,it usually has a thicker wall than the othertypes of pipe. For this reason, it is heavier.Also, since it is virtually hand made, it ismore expensive. Strength in the axialdirection is higher than filament woundpipe. Because the pipe is hand made, it issubject to wider manufacturing tolerancesthan the other types of pipe. This is1-27-2018Page 9 of 16especially important to the support designerwho is responsible for the designed fit ofsupports. Contact molded pipe is highlyrecommended for use where it might besubject to a severe exterior environment.Fittings are normally joined to the pipeusing the butt and strap method.Filament Wound. A high glass content andprecise fiber orientation make this type ofpipe ideal for pressure applications.Machines are used more in its fabrication, sothe tolerances are closer, the mechanicalproperties more consistent, and theproduction cost is lower than for contactmolded pipe. Due to the low resin to glassBritt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, ALfiber ratio, a corrosion liner of a minimum100 mils should be provided. Since theaxial strength of filament wound pipe is lessthan that for contact molded pipe, at thesame pressure rating, the filament woundpipe will require a much closer supportspacing. This is due to the thinner wallcommon with filament wound pipe. Thepreferred method of joining fittings and pipeis the butt and strap method, althoughseveral manufacturers provide tapered belland spigot ends for joining pipe and fittings.The bell and spigot joint is an adhesive jointthat is dependent on the glue line betweenthe bell and spigot.Centrifugally Cast. This type of pipe isalmost fully machine made, and it providesthe most consistent mechanical propertiesand the closest tolerances. It has a lowerglass fiber content than filament wound pipeand features higher corrosion resistance.The smooth outside diameter also facilitatesa more consistent support design. Cast pipe,due to fiber orientation and higher glasscontent, has a higher axial strength thaneither the filament wound or contact moldedpipe. Cast pipe has an unreinforcedcorrosion liner which is susceptible todamage by impact, but if the pipe is properlyhandled and supported, it should pose noproblems. Fittings are normally of thesocket weld type that can be overwrapped ifadded joint security is desired. However,with correct installation procedures andinspection, the overwrap is generallyconsidered unnecessary.Design Considerations1-27-2018Page 10 of 16Contact molded FRP pipe, made accordingto PS 15-69, is normally rated by pressure inincrements of 25 psi up to 150 psi. Standardmachine made pipe does not follow this typeof rating and the designers should refer tothe ultimate pressure rating listed in themanufacturer's catalog. It is important tonote that these ratings are based on theallowable pressure of a continuouslysupported pipe subject to pressure stressonly. Since piping systems are almost nevercontinuously supported, the stresses ofbending must be considered whendetermining the allowable working pressureof an FRP pipe. The equations presented inthe section on Support Design take thesestresses into account.Wall thicknesses are based on a 10:1 safetyfactor in the hoop direction and it iscustomary to use a 5:1 or 6:1 safety factor inthe axial direction. By maintaining thesesafety factors in the design, stress risers inelbows and other fittings will be within theallowable stress limit.The method of design layout preferred byBritt Engineering Associates is an anchorto anchor design. This design method canbe economical and offers many advantages.The anchor to anchor system is more rigidand less susceptible to damage due todynamic loading. This system alsoprovides a means for controlling expansion(thermal and pressure), thereby reducing thelength of offsets and eliminating the needfor expansion joints. Anchors are placed oneither side of every change in pipe directionand as near to the fitting as possible. TheBritt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, ALamount of structural steel required to absorbthe loads imposed on the anchors can beminimized by keeping the pipe elevationclose to the steel and by utilizing tensionmembers between anchors. It is importantto recognize that the pipe must be guidedbetween anchors to prevent buckling. Incases where there are long straight runs,anchors should be placed no more than 150to 200 feet apart.design techniques presented here will help tostandardize a conservative design approach.Beyond this, a great deal of work isnecessary to standardize installationtechniques, especially the methods forfabricating joints.When the anchor to anchor design cannot beused, and the pipe must be hung with rodhangers, a great deal of care should be takento ensure flexibility. However, a pumpedsystem that is too flexible will vibrate anddestroy itself if vibrations are within theresonant range. Excessive stresses can alsobe induced by wind loads. To reducevibration and wind load effects, the pipeshould be laterally restrained at specifiedintervals along the pipe. These restraintsshould not be located near changes indirection where offset legs are required forflexibility.Keep the pipe run away from high trafficareas where damage from equipment impactis likely.Design TechniquesMany piping system failures that occurduring hydrostatic testing, or even afteryears of service, have been attributed to poorworkmanship. These failures are due to anoverstress condition which was caused byeither poor workmanship or unsatisfactorydesign. The task of the designer is toeliminate, as much as possible, thelikelihood of failure. With sufficient effortspent on the design and in the instruction ofinstallation personnel, failures can beeffectively reduced. It is hoped that the1-27-2018Page 11 of 16In an effort to reduce the possibility offailure, the designer should seriouslyconsider the following: Keep flange joints to a minimum. Provide vents at each high point. Provide drains at each low point orpocket. (Drains with blind flanges willallow the line to be drained if repairs arenecessary.) Ensure that all supports, anchors, andguides are installed prior to the hydrotest. (This cannot be overemphasizedsince the pipe system can be severelydamaged without proper pipesupport.) All valves and valve operators, orcomponents in the system, must beindependently supported. Riser supports for long vertical runsshould be guided or restrained toreduce vibration and wind loadeffects.When setting up for hydro testing, open allhigh point vents to remove all air andconnect the pump to the lowest point in thesystem. (The pump should be a small,positive displacement pump [3 to 5 gpm]Britt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, ALand should be equipped with a pressureregulator that will allow the system pressureto build slowly.)Economic ConsiderationsWith material prices and the cost oflabor rising frequently, a costcomparison between an FRP system andany other is meaningless since cost datais out of date before it is printed. FRP isnormally selected because of itscorrosion resistance. However, oneimportant point that should be madeconcerning any comparison is that thetotal installed cost to be considered.Many studies do not include data on thesupport system required for FRP pipe.This is because most analysis procedurestend to regard all piping systems asbeing supported in the same manner andat the same relative cost. In addition, thecost of auxiliary steel, and the labornecessary to install that steel should beevaluated.The service life of each system is animportant factor and should be includedin the evaluation if sufficient historicaldata can be obtained. Many designerswould probably elect to use materialsother than FRP when the installed priceof the two systems is relatively close, butthe extended service life of FRP systemswill usually be more favorable.Generally, experience at BrittEngineering Associates has indicatedthat FRP systems are more economicalthan other systems in pipe sizes above 41-27-2018Page 12 of 16inches where special metallic materialsare considered.Applicable Codes and StandardsThere are very few codes or standardsapplicable to the design of FRP pipingsystems. The designer should befamiliar with the American NationalStandard Code for Pressure Piping(ANSI) B31.3, although it deals mainlywith metallic pipe it has been expandedto cover non-metallics includingthermoplastic and thermoset materials.The only other standard that could proveuseful for design purposes is the NBSVoluntary Product Standard PS 15-69,which covers custom contact moldedFRP equipment. This document is nolonger published by NPS, but copies canbe obtained through some of the resinand glass manufacturers. The tables forpipe included in this Standard should beused with care.The American Society for Testing andMaterials (ASTM) has publishedstandards for Plastic Pipe and BuildingProducts, Section 8, Volume 08.04,1993. This document is a compilationof test procedures and methods forestablishing material and mechanicalproperties for plastics used in piping.A number of codes and standards arebeing developed to promotestandardization of the product, but theyare not available at this time. Oneexcellent guide that is available is a bookentitled "Corrosion -- Resistant PlasticBritt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, AL Composites in Chemical PlantDesign" by J. H. Mallinson, publishedby Marcel Dekker, New York , 1988.Another book that provides goodoverall coverage of the use of FRP is"Fiberglass Reinforced PlasticsDeskbook" by N.P. and P.N.Cheremisinoff, Ann Arbor Science,Michigan, 1978.The Composites Institute of theSociety of Plastics Industry publisheda "Fiberglass Pipe Handbook" in 1989that is a document that was written bythe Fiberglass Pipe Institute, New York.The handbook is a compilation oftechnical sections covering above andbelow ground piping systems, and whileit is an excellent reference for pipingdesign, the methods of analysis anddesign of supports presented in this bookare not the same as recommended in thiscatalog.The use of expansion joints andexpansion loops are very rarely used inpractice, and the supports recommendedin the handbook should not be usedexcept in very light duty service. Layout of Piping SystemsThe preliminary piping layout for FRPpiping is the same as for any othersystem (Figure 2). Once a generalpiping arrangement has been selected, anisometric of the system should be madeand the following steps taken:1-27-2018 Page 13 of 16 Locate available support steel andestablish the location of additionalsupport steel as required. Existingbridges, pipe racks and buildingstructural steel will establish theavailable support spacing.Locate anchors at each change inpipe direction and as close aspossible to elbows.Locate riser supports and componentsupports. Riser supports can betentatively located on 10-foot centersuntil calculations are made.Establish support design criteria andpipe wall thickness required using theequations in the section on SupportDesigns factoring the operatingtemperature and pressure of the system.An iterative process is employed toobtain wall thickness and to defineacceptable support spans.Tabulate support design criteria shownin Table 1 and rearrange support spacingand anchor locations on the isometric tomeet design criteria. Add guides atlocations determined in the table.Check offset leg requirements betweenanchors at directional changes. Relocateanchors as required to meet offsetrequirements.Rearrange riser support locations. Thedistance between centers should notexceed the guide spacing. In areas whereoffset leg requirements cannot be met,consideration should be given toBritt Engineering Associates, Inc.

Britt Engineering Associates, Inc.Birmingham, ALrerouting the pipe to provide moreflexibility.Vibration - Pump or equipment vibrationsare usually absorbed by the piping system;however, it is a good practice to use anexpansion joint with tie rods at the pumpdischarge if the discharge pipe can beanchored. Care must be exercised to insurethat the pump is capable of handling thethrust loads and/or thermal loads that aredeveloped by the fittings.Water Hammer - There are severalrecommended method

frequent piping failures were causing concern. One of the major manufacturers of resins determined that most of the piping failures could be eliminated through the use of proper supports, guides, and anchors. T