application of gfrp

6.31Application of FiberglassReinforced Plastic to CorrosionResistant Equipment (for PipingSystems and Pressure Vessels)R. J. LEWANDOWSKI and W. F. BRITT, JR.

Britt Engineering, Inc., Birmingham, AL, USA

6.31.1 INTRODUCTION 2

6.31.1.1 Resins and Reinforcements 26.31.1.1.1 Polyesters 26.31.1.1.2 Vinylesters 36.31.1.1.3 Resin selection 36.31.1.1.4 Reinforcements 3

6.31.2 APPLICATIONS AND USES 3

6.31.2.1 Applications 36.31.2.2 Uses 3

6.31.3 DESIGN Of CORROSION RESISTANT FRP 4

6.31.3.1 Storage Tanks and Process Vessels 46.31.3.1.1 Operating conditions 46.31.3.1.2 Method of fabrication 46.31.3.1.3 Laminate design 66.31.3.1.4 Stress analysis and vessel design 76.31.3.1.5 Special considerations 7

6.31.3.2 Piping Systems 86.31.3.2.1 Background 86.31.3.2.2 Laminate design 96.31.3.2.3 Piping design 96.31.3.2.4 Mechanical properties 106.31.3.2.5 Comparisons 116.31.3.2.6 Design approach 116.31.3.2.7 Hydrostatic testing 146.31.3.2.8 Economic considerations 156.31.3.2.9 Applicable codes and standards 156.31.3.2.10 Layout and design of piping systems 156.31.3.2.11 Vibration, water hammer, and cavitation 166.31.3.2.12 General 19

6.31.3.3 Approaches for Design of Supports 206.31.3.3.1 Fitup of support 206.31.3.3.2 Location of supports 206.31.3.3.3 Location of guides 206.31.3.3.4 Location of anchors 206.31.3.3.5 Fixing of anchors 206.31.3.3.6 Riser supports 21

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6.31.3.3.7 Supports for insulated pipe 216.31.3.3.8 Component supports 216.31.3.3.9 Thermal expansion 216.31.3.3.10 Coatings 21

6.31.3.4 Support Illustrations 21

6.31.4 CONCLUDING COMMENTS AND FUTURE PROJECTIONS 22

6.31.5 REFERENCES 25

6.31.1 INTRODUCTION

The use of fiberglass reinforced plastic (FRP)materials has grown considerably over the past20 years and many successful designs haveevolved to become standards. Basic rules fordesign parallel those that have been successfulin steel tank design for close to 100 years.Engineers and designers involved in the appli-cation of FRP would be wise to follow thosesuccessful design rules while keeping in mindthat FRP is a very different material. Under-standing the unique mechanical properties ofFRP is essential and as successful new designsevolve through practical applications orthrough new analytical tools, we will see thestandards develop for FRP materials. The ref-erences presented in this chapter have beenproven through experience and the analyticalmethods that are included are the result oftesting and successful case histories. Some ofthe design considerations are the result of ex-periencing failures. As the applications of thismaterial continued to expand, it is most impor-tant that design rules are developed from thepositive applications, and lessons are learnedfrom failures.

The development of materials has been thesingle most important factor in the growth ofFRP in the process industry. Safe design meth-ods, quality fabrication, and improvements inspecifications have kept the growth steady. Inyears past, FRP materials were used to solvecorrosion problems before proper design meth-ods were developed and the result almostcaused the demise of FRP, especially for appli-cations in process piping.

A great deal of work is still required toquantify mechanical properties, behaviorunder various environments, creep, long-termbehavior, the nature of stress concentrations,precise design limits, and unique characteristicsof shapes. As this work progresses the designerwill be given the tools to bring factors of safetywithin cost efficient limits and when this plat-eau is reached the use of this material will growexponentially.

6.31.1.1 Resins and Reinforcements

Thermoset FRP basically derives its mechan-ical properties from the reinforcement and itschemical resistance from the resin matrix. Thetypes of resins involved are all polyester andvinylester since these offer the cost benefits tocompete with alternate materials. An emergingapplication area is the use of thermoplasticliners for special applications.

6.31.1.1.1 Polyesters

The most common thermoset polyestergroup used today is based on the combinationof a glycol and orthophthalic acid/maleic acidreacted together. Unfortunately these resins arevery useful for producing marine, bathware,and other items but their resistance to acids,caustics and their hydrolytic stability at ele-vated temperatures virtually rule out their usein corrosion applications.

Isophthalic acid and specialty glycols yieldresins which have improved hydrolytic stabilityand resistance to acids. Terephthalic acid andglycol based resins have higher molecularweight and hydrolytic stability. Both the isoand tere resin family of resins are generallyacceptable for applications below 140 8F and apH of 8. They must not be used for caustics,bleaches, and similar reactive chemicals. Theirmechanical properties are most applicableunder static stress conditions. The designershould be careful with situations where highcreep, fatigue, or thermal stresses are involved.Resilient polymer structures are favored inthese cases.

Atlas chemical was basic in propoxylationtechnology and found that a propoxylatedbisphenol A structure was an ideal glycol forreaction with maleic acid to form a polyester.Together with a team from E. I. DuPont deNe-mours they ascertained that these polyesterswere quite resistant to a broad range of corro-sive chemicals. These resins became the fore-most component in the ªcorrosion fieldº for the

Application of Fiberglass Reinforced Plastic to Corrosion Resistant Equipment2

replacement of costly alloys to handle difficultcorrosion environments.

6.31.1.1.2 Vinylesters

In the early 1960s scientists from both ShellOil and Dow Chemical were attempting toexpand the epoxy market. They discoveredthat polymeric bisphenol A epoxies could bereacted with acrylic acids yielding a structurewith pendant vinyl groups. These resins couldbe reacted with styrene to yield very resilientthermoset structures. This chemistry has beenextended to other epoxy structures to give ªvi-nylestersº with special properties. Chemists atICI Americas soon discovered that the propoy-lated bisphenol intermediate used to make theAtlas polyesters could be reacted with an iso-cyanate and then used to form a urethanemodified vinylester.

6.31.1.1.3 Resin selection

After completing definition of the containedfluids and the operating conditions, the de-signer should contact the resin manufacturerto assist in the selection of the most cost-efficient resin. The resin manufacturer willalso make recommendations for selecting theoptimum corrosion barrier and will suggest thebest cure system for the application. After themanufacturing method is defined, it is recom-mended that the resin manufacturer be con-tacted to insure that the selected resin iscompatible with the manufacturing process.Whether the tank is to be filament wound orhand lay-up construction will sometimes neces-sitate a modification of the resin selection. Themanufacturer will need to be informed of anydesign or operating changes before approvalfor fabrication.

6.31.1.1.4 Reinforcements

Except in very special cases, fiberglass is thereinforcement of choice for most designers ofindustrial tanks and process vessels. ªEº (elec-trical) glass is favored for structural laminatesbecause of its enormous strength. ªCº (chemi-cal) glass is the predominant selection for theinitial corrosion barrier surface because of itschemical resistance. Special high strength rein-forcements such as Kevlar, ceramic, carbon,graphite, and some special thermoplastic fibers

might be selected when high strengths are man-dated by special design requirements. For themost part these special fibers are not widelyused because of cost.

6.31.2 APPLICATIONS AND USES

6.31.2.1 Applications

Today all of these specialty structures areutilized to produce corrosion-resistant matricesthat are very corrosion resistant. The Het(chlorendic anhydride polyester) acid resinsare still used in various duct applications andfor strong oxidants like chromic acid.

The BPA (bisphenol A fumerate) polyesterscover the widest range of chemical applications.They resist both acid and caustics environmentsas well as oxidizing materials. A flexible versionis suitable for filament winding and many of theoriginal filament wound chemical tanks madewith this version are still in service over 30 yearslater.

The vinylesters give tough and resilientmatrices. They present very significant benefitsespecially in filament wound structures. Mostpipe applications are produced with vinylesters.Whenever strong stress conditions are to behandled, such as occurs in many process vessels,the vinylesters are the matrices chosen. Vinyl-esters give good acid resistance, moderate alka-line resistance, and an acceptable level ofresistance to a broad range of oxidative chemi-cals. The urethane-modified vinylesters are re-silient and tough with the benefits of improvedcaustic resistance, temperature resistance, andwetting properties.

6.31.2.2 Uses

When properly incorporated with glass rein-forcement, these resins produce structures withdocumented, predictable strength properties.These in turn can be used to design tanks,scrubbers, pipe, duct and various other FRPequipment.

The mechanical properties used in the designof FRP equipment include the flexural strengthand modulus, tensile strength and modulus,compressive properties, Poisson's ratio, andheat distortion temperature. It is important tounderstand that the structural properties of anycomposite are a function of glass type andcontent, glass orientation, and resin properties.It is imperative that the resin system be used inaccordance with the guidelines of the manufac-

Applications and Uses 3

turer to insure proper cure so that optimummechanical properties and chemical resistanceis achieved. All major resin manufacturers pub-lish comprehensive corrosion guides and in-structive bulletins to assist the user.

6.31.3 DESIGN OF CORROSIONRESISTANT FRP

6.31.3.1 Storage Tanks and Process Vessels

Improvements in resins have made contain-ing corrosive fluids and vapors somewhat easierfor the designer but containment is still a ser-ious problem for long-term service. It has beenaptly stated that all tank and piping failures arethe result of an overstress condition. In manycases corrosion was thought to be the primarycause of failure and in the past that was fre-quently true. Even so, the degraded laminatewas overstressed as laminate strength was lost.The newer resins provide much better protec-tion of the laminate but FRP equipment mustbe carefully designed to insure that total stres-ses are held to approximately 10% of the ulti-mate throughout the operating range of thetank or equipment.

There are several important steps that thedesigner must take to insure that the equipmentis capable of reaching its maximum service life.A successful design includes:

(i) Complete identification of exact operat-ing conditions

(ii) Resin selection(iii) Reinforcement type(iv) Method of fabrication(v) Laminate design(vi) Stress analysis and vessel design.

Experience has also shown that attention mustbe given to quality control to insure that fabri-cation techniques meet the requirements of thedesign. All of the care exercised during designcan be lost due to improper fabrication or poorquality and workmanship.

6.31.3.1.1 Operating conditions

A successful design must begin with a com-plete identification and understanding of oper-ating conditions. The chemical environment,concentrations, specific gravity, and maximumtemperature of the contained fluid will set therequirements for resin selection and mechanicalproperties of the laminate. The designer can usea design data sheet, such as the User's BasicRequirements Specification (UBRS) form of-fered in the ASME Standard RTP-1 (1993), toidentify all critical operating and design condi-

tions. Most standards, such as ASTM D 3299and ASTM D 4097, or data sheets similar toPressure Vessel & Storage Tank Data Sheet,Figure 1 are specifically for cylindrical tanksfor above ground, vertical installations. Thesetanks are limited to atmospheric pressures andgenerally have a domed top and flat bottom.Design or operating conditions for other tankconfigurations are shown in Figure 2 and willrequire stringent analysis by the designer.

The designer must define all other conditionsthat might subject the vessel to loads other thanhydrostatic loads. Wind, seismic, and snowloads must be incorporated into the design.Equipment attached to the tank, such as agita-tors, heaters, relief or control valves and accessladders and platforms will add to the designloads and must be considered. In many casesthe vessel must accept heavy external pipingloads and the designer must make special ac-commodations for weight, thermal, and dy-namic loading imposed by the piping system.Pumps can sometimes induce large dynamicloads, thermal loads, or vibrations that mustbe accommodated in the design.

Defining these design requirements are criti-cal to a successful design. This information isused to select the resin, glass reinforcement, andmethod of fabrication. Any changes to the ser-vice conditions that may be made by the owneror process engineer after the design is completecan negate the design. There have been a num-ber of tank failures caused by a change in theprocess fluid or operating conditions by theowner after the tank has been put into service.A well-designed tank will call for a prominentlydisplayed nameplate that incorporates all of thedesign data to help prevent misuse.

6.31.3.1.2 Method of fabrication

All tanks are manufactured either by using ahand lay-up method (HLU) sometimes referredto as a contact molded method, or by filamentwinding (FW). Filament winding, except invery rare instances, applies only to the manu-facture of the straight shell of the tank. HLUcan be used to manufacture the straight shellbut is the only method used for making theheads of all tanks.

(i) Hand lay-up (HLU)

ASTM D4097 provides a comprehensive de-scription and specification for this process. Thelaminate is built up of alternate layers of awoven roving glass material, usually ªEºglass, and a chopped strand roving bound inthe form of a mat. Mechanical properties are


presented in the standard with ultimate tensilestrength varying between 9000 and 15 000 psidepending on the thickness.

This process offers exceptional corrosionresistance due to the high resin content wherethe to glass to resin ratio ranges from 0.3 to 0.4.A corrosion barrier thickness of 0.100º isstandard and consists of a ªCº veil and two1.5 oz./ft2 mat layers.

(ii) Filament wound (FW)

Filament winding is a popular method offabricating but it is applicable only to surfacesof revolution. Because it offers a much highertensile strength than the hand lay-up methodit becomes a more cost-effective method ofproduction, especially when manufacturingmore than one tank of the same size. Strength

Figure 1 Pressure vessel/storage tank data sheet (cylindrical, above ground, vertical installation).

Design of Corrosion Resistant FRP 5

is derived from the glass orientation, preten-sioning of the glass roving, and the high glass toresin content. The glass to resin ratio can be ashigh as 0.75 by weight, but the low resin contentmeans that this laminate is not as corrosionresistant as the HLU laminate. The same0.100º corrosion barrier used in the hand lay-up method is standard for FW construction(ASTM 4097).

The manufacturing equipment used to fila-ment wind is more expensive than that requiredfor hand lay-up but production is much fasterand less hand labor is required. Strength is themain advantage of FW structures but an addi-tional advantage is the highly consistent glasspattern that is precisely controlled by the wind-ing equipment. Wall thickness and resin to glassratios are also consistent.

6.31.3.1.3 Laminate design

Composites obtain their strength from thereinforcement, in most cases fiberglass, andderive their corrosion resistance from theresin. One of the most attractive features ofglass reinforced plastics is the wide range oflaminate designs that are available. Manufac-turers of composites can easily provide anyglass orientation, thickness, or combinationsof glass types that the designer can imagine.Directional strength is obtained by aligning theglass strands parallel to the axis where maxi-mum strength is required. By placing equalamounts of glass in a bidirectional pattern,strength is highest in these two directions. Ap-plying the glass in random pattern results in alaminate with equal strength in all directions.

With this latitude for design, it becomes pos-sible to apply these three patterns to obtain al-most any laminate properties that a designwould require. There are analytical programsavailable such as ªTriLamº and ªSuperLam,ºproduced by Osborne Composite Engineering,ON,Canada, that allows the designer tomix andmatch glass types, orientations, glass weights,resin types and ratios, and thicknesses to obtainthe most efficient composite available for a par-ticular set of requirements. Fortunately in thedesign of tanks there are a few standard laminatedesigns that have been developed which havebeen extremely successful and cost-effective forthe production of most tanks and vessels.

FW tank shells are manufactured using an80±858 wind angle. A 908 angle would be a flatwind angle and would provide maximum hoopstrength. The slight angular pitch, 80±858, of-fers a component of axial strength (along theaxis of the tank) to pull the shell from themandrel and provides the strength needed tolift the tank. Where additional axial strengthis required, several layers of low angle glass(30±458) might be intermixed during the wind-ing process. Some manufacturers have also ap-plied layers of a knitted (textile style) cloth withall of the glass oriented in the axial direction.When knitted cloths are used it is necessary thata mat layer be applied before and after thecloth. These mat layers enhance the bondingof the two types of glass.

Hand lay-up shells are manufactured usingalternate layers of mat and woven roving. Thisprocedure produces both a uniform bidirec-tional pattern with the woven roving but alsoa multidirectional pattern with the mat layers.The woven roving provides the hoop and axialstrength while the mat provides a uniformmultidirectional strength. Another key featureof the mat layers is the bond strength that itprovides between the layers of woven roving.

Figure 2 Various tank configurations.


6.31.3.1.4 Stress analysis and vessel design

The geometry of the tank will dictate themethod of analysis used to design the tank.Vertical, cylindrical tanks with flat bottomsare the simplest designs and usually followlong established rules as specified in API 650,ASTM D 3299, ASTM D 4097, and ASMERTP-1 (1993). Each of these standards providesdesign rules for calculating wall thickness, jointdimensions, and nozzle requirements. Calcula-tions for the top heads are not provided in APIor ASTM standards but Part 3 of RTP-1 pro-vides a comprehensive method for calculatingthe heads, external loads, stiffeners, and offersrules for the reinforcement of openings andattachments for flanges.

Design by stress analysis is included in Ap-pendix M-4 of RTP-1 and is an adaptation ofSection VIII, Div. 2, of the ASME Boiler andPressure Vessel Code. This procedure is a rig-orous engineering exercise and should be per-formed by a professional engineer withcomposite experience. There are other methodsof analysis that will provide a satisfactory de-sign. The use of finite element analysis (FEA)has grown in popularity and is becoming anacceptable method of design but it is also arigorous procedure and is highly dependenton the accuracy of the definition of the mechan-ical properties of the laminate.

The design procedures presented in Megyesy(1995) can be employed but the engineer musttake care to use the properties of the compositeand insure that factors of safety comply withthe referenced standards and specifications.Mallinson (1988) also offers an excellent pro-cedure for the design of vertical, cylindricalvessels as well as other tank configurations.This reference provides many design examplesas well as details for nozzles, stiffeners, lugs,and special consideration of agitators, externalpressure, knuckles, and special openings.

6.31.3.1.5 Special considerations

All of the above references will guide thedesigner and provide sufficient background in-formation on the selection of materials, analy-sis, and fabrication and offer most of the detailsused in the design of standard tanks. However,the designer should be aware of several specialconsiderations when designing FRP tanks.These are listed for the designer's review, andwhile most of the references do not addressthese special details, these have been found byexperience to be important issues.

Secondary bonds. Structural welds are alwaysapplied to the outside of the tank and only

under special conditions installed inside of thetank. Corrosion barriers can be applied insidethe tank but structural welds applied inside thetank are prone to delamination when hydro-static loads are applied. Laminates shrink whenthey cure and this shrinkage generates a shearforce that works against the bond strength ofthe laminate.

Tank bottom. Flat bottoms should be at-tached to the tank shell by means of a standardknuckle as defined in the ASTM Standards,RTP-1, and other referenced documents.RTP-1, Section 4, presents several knuckle de-signs that have proven successful. Recent de-signs have incorporated an internal knuckle,described as an internal ªflexibleº or in somecases as an internal ªrigidº knuckle. This designemploys a heavy structural lay-up inside thetank and has been found to develop stresscracks around the perimeter of the tank. Thecracks usually occur near the lower tangentwhere the curved surface ties into the tankfloor. While repairs can be made, this designhas required frequent maintenance and couldfail catastrophically unless carefully inspectedon a frequent basis.

Tank top. Elliptical or flanged and dishedheads should be detailed by the designer andshould include fabrication details describing theweld to the tank shell. Recommended detailsare shown in Part 4 of RTP-1. Flat, cone, orspherical tops should incorporate a transitionradius to the tank shell or should be flanged tomate with a body flange on the tank.

Flanged nozzles. Many tank manufacturersand designers specify 25 psi rated flanges formost tank storage tanks. A 100 psi rated nozzleis recommended as a minimum for all nozzlesexcept for manholes and tank vents, where a 25psi rating is acceptable.

Vents. Vents must be sized to accommodatethe largest inlet nozzle. A general rule is tospecify a vent size at least one size larger thanthe inlet. Where more than one inlet is used thevent must be sized to accommodate both.

Foundations. The foundation must be flatwithin 1/4º over the entire tank area. Voids orlow spots must be grouted. After the concretehas cured, a corrosion resistant top coat shouldbe applied and allowed to cure. Two layers ofbuilding felt should be smoothly rolled over thesurface to cushion the tank.

Insulation. Insulated tanks should employclips or support rings to keep the insulation inplace. Rings should be providedwith weep holesto allow condensation to drain. A 1/8º outerskin of FRP, pigmented to reduce UV degrada-tion, provides an excellent cover for the insula-tion. Glass rock insulation has been a materialof choice where fire protection is required.


Nozzle load. All nozzles 4º in diameter andbelow should be gusseted to reduce nozzlestresses caused by excessive piping loads. Be-fore the tank design is completed it is recom-mended that the tank designer check all pipingloads into the tank nozzles. In cases wherepiping loads cannot be reduced by re-routingthe pipe or by supports, the tank and/or thenozzle must be reinforced so that the pipe doesnot overstress the tank or nozzle.

Hold down lugs. Hold down lugs should bemade of FRP, stainless steel, or in some casesgalvanized steel depending on the service of thetank. Lugs should not be drilled for a singleanchor bolt but should incorporate a fish plateor hold down clip that is anchored separatelyfrom the tank lug. This arrangement provides asecure attachment without restricting thermalexpansion of the tank. In a number of cases, theanchored lug has caused severe buckling andradial cracking of the tank bottom.

Lifting lugs. Lifting lugs use the same materi-als as for hold down lugs. The lifting lugs mustbe designed to allow the tank to be lifted ontothe foundation without inducing buckling loadsinto the top and shell and should have a designload factor of 10. The designer should provideinformation on the drawing that specifies de-tails for lifting. Cable connections, spreaderbars, and tag lines should be called out. It isgood practice to call for a special permanent tagto be attached to the tank that specifies liftingdetails and the empty weight of the tank.

6.31.3.2 Piping Systems

6.31.3.2.1 Background

In the late 1960s and early 1970s, FRP ma-terials were being developed that would bringthe market for FRP pipe to new heights. FRPwas specified in many applications where onlyspecialty alloys had been used and as the appli-cations expanded, FRP was becoming the com-plete problem solver for corrosion service.Resin manufacturers were developing newpolyesters and vinylesters that were tougherand more resilient. Manufacturers were devel-oping fabrication methods that improved qual-ity and reduced costs. In 1974 several businessprojections indicated that FRP was to be thegrowth industry of the future but at about thesame time some plant owners and engineersbegan to experience frequent piping failures.Many users were questioning the ability ofthis material to handle the operating stress ofprocess piping.

One of the major producers of resins began astudy in an attempt to understand the cause of

these frequent failures. They discovered that95% of all failures were tensile failures in theaxial direction of the pipe and were the result ofaxial thrust or bending. Also of interest, 95% ofthese failures occurred at pipe joints. This studyled engineers to believe that by restraining thepipe in the axial direction and by guiding thepipe to reduce bending, the failures could beeliminated. Support spans were reduced tocompensate for pressure stress, which adds tothe bending stresses. Almost all span calcula-tions had been based on simple bending stressinstead of total stress resulting in extremelylong support spans. The most important find-ing from this study was that FRP piping couldbe successfully used when careful analysisof support, guide, and anchor placement isconsidered.

The responsibility of the engineer is to insurethat the piping system operates within allow-able stresses when the system is subjected to themost severe operating conditions. The allow-able stress is usually 0.100 times the ultimatestrength for hoop stress and 0.050 times theultimate strength in the axial direction. Themajor difference between the design of a pipingsystem and a tank is that the tank is one finitestructure with easily defined boundariesÐapiping system is a complex three-dimensionalframe that has three degrees of freedom. Anengineer usually performs the stress analysis,however, the layout of the FRP piping system isbest left to an experienced piping designer. Thisperson learned the art of piping by years ofpainful experience with very little help fromtextbooks or handbooks.

If the designer does his job well, the layoutwill consider expansion, support locations, ac-cess to equipment and control stations, and willprovide access and clearance for maintenance.The designer will find that FRP piping is some-what more complex than metallic piping be-cause of the lower strength, higher coefficientof expansion, installation differences, and be-cause FRP requires positive restraint to keepstresses within acceptable boundaries. A wellplanned routing will allow the engineer to ana-lyze the system and with adequate supportprovisions, the system stresses can becontrolled.

Before laying out the system the designer andengineer are referred to several technical papersthat address important considerations for suc-cessful design (Escher, 1979; Britt, 1979, 1983).Britt (1979, 1983) provides a simplified methodof analysis for FRP pipe that is presented in thischapter. There are several formal stress pro-grams that are designed for PCs that havebeen used by experienced engineers but with agreat deal of caution since the programs were


not primarily designed to handle the uniqueproperties of nonisotropic materials such asFRP.

6.31.3.2.2 Laminate design

(i) Hand lay-up

NBS PS 15-69 (1969) provides a descriptionof the hand lay-up pipe. The laminate beginswith a corrosion liner consisting of a resin-richlayer that is reinforced with a ªCº veil and two1.5 oz./ft2 ªEº glass mat layers. The structuralwall consists of alternate layers of 24 oz./yd2

ªEº glass woven roving and mat. The methodof construction provides a resin-rich laminatethat is ideal for corrosion service.

(ii) Filament wound

ASTM D 2996 describes the process for fila-ment-wound pipe. This type of pipe offers aneconomical method of manufacture and pro-vides exceptional hoop strength. The corrosionliner is applied by hand lay-up on a rotatingmandrel in exactly the same way as the handlaid-up pipe. The standard liner is the sameglass material and thickness. Once the linerhas gelled a pretensioned glass roving iswound over the pipe to form a structural

cage. The accepted angle of wind is 54 + 18measured from the axis of the pipe. The windangle was mathematically derived to balancethe axial and hoop stress.

(iii) Centrifugally cast

The manufacture of this pipe is described inASTMD2997. Glass fiber is in the form of mat,woven roving, or chopped strand. The amountof glass is determined by the desired wall thick-ness. The glass is inserted into a mold which is atube with the required inside diameter and thetube is rotated at high speeds. Centrifugal forcepresses the glass against the wall of the spinningtube and as the resin is injected it is also forcedto the wall, fully wetting the glass. This processproduces a laminate that is completely free ofair and results in a smooth, resin-rich innerlayer for corrosion resistance. This methodproduces a very uniform pipe with excellentmechanical properties (see Table 1).

6.31.3.2.3 Piping design

The following steps concerning the designand installation of FRP pipe and supports areprovided as a help to the designer or engineer.These design steps are intended to serve as aguide to the proper use of the supports, and

Table 1 Pipe physical properties comparsion.

Filamentwounda

Centrifugallycastb

Hand lay-up(contacted molded)

Low carbonsteel

Modulus of elasticityin tension axial(77 8F psi)

1.0±2.76 106 1.3±1.56 106 0.8±1.86 106 3.5±4.06 105 296 106

Ultimate axial tensilestrength (77 8F psi)

8000±10 000 25 000 9000±18 000 6000±7000 50 000±70 000

Ultimate hoop tensilestrength (77 8F psi)

24 000±50 000 25 000 9000±10 000 6000±7000 50 000±70 000

Modulus of elasticityin beam flexure(77 8F psi)

1±26 106 1.3±1.56 106 1.0±1.26 106 3.56 105 296 106

Thermal expansion(in. /in/8F)

8.5±12.76 1076 136 1076 156 1076 3.06 1075 6.06 1076

Heat deflectiontemperature(264 psi 8F)c

200±300 200±300 200±250 155±165 N/A

Thermal conductivityBTU/h/ft2 8F/in)

1.3±2.0 0.9 1.5 1.0±1.4 300±350

Specific gravity 1.8±1.9 1.58 1.3±1.7 1.3±1.6 7.85

Source: Escher (1979). For exact values contact pipe manufacturer.aValues shown for filament -wound pipe are based on pipe wound at an angle of approximately 548 bAs published by a leading manufacturer ofcentrifugally cast pipe.cASTM D 648.


while it is impossible to cover every pipingcondition, experience indicates that approxi-mately 95% of the design requirements can bemet through the use of these procedures. If thedesigner is faced with special conditions where aspecial design might be required, he/she shouldcontact the engineer for assistance.

(i) Review piping specifications.(ii) Review piping drawings.(iii) Review structural drawings.(iv) Review valve and fitting specifications.(v) Locate possible hanger locations.(vi) Analyze thermal movement, stress, and

flexibility of the piping system.(vii) Calculate hanger loads.(viii) Select hanger types.(ix) Check piping and hanger clearance

around existing piping structure and equip-ment.

The principles of design and analysis for FRPpipe differ considerably from the principles ofdesign for metallic pipe. The analysis of steelpipe normally begins with maximum flexibilityand the final support-guide-anchor design endswhen allowables are achieved. When dealingwith FRP pipe, the analysis normally beginswith a fully anchored system and the final sup-port-guide-anchor configuration is establishedwhen the minimum stress condition is reached(based on the available structural steel).

The fully anchored FRP piping system isoften referred to as an anchor to anchor system.This simply means that an anchor is placed ateach end of a straight run of piping. The pipe isrestrained from growing thermally by the an-chors and is guided to prevent buckling. Thisarrangement is never considered with metallicpipe but the low compressive modulus of FRPallows anchoring. The anchor loads are nor-mally less than 1/60th that of steel but must beconsidered in the structural design of the sup-port system, especially in large-diameter pipe.

6.31.3.2.4 Mechanical properties

After the selection of a resin system, determi-nation of the type of pipe must be made. Thereare three major categories of FRP pipe con-struction: (i) contact molded, (ii) filamentwound, and (iii) centrifugally cast. The mechan-ical properties of the pipe are closely linked tothe method of fabrication and those propertiesvary considerably among the three types.

Despite conjecture as to the advantages anddisadvantages of each type of pipe construc-tion, it has been found that any of the three canbe utilized if the pipe is of high quality and if thesystem has been properly designed and sup-ported. The specific mechanical properties of

the pipe selected are incorporated into the de-sign of the system. This includes the locationand type of support. The mechanical propertiesinherent to the method of pipe fabrication arediscussed in Section 6.31.3.2.12.

The most important factor in the design of apiping system is the determination of the me-chanical properties of the pipe over the opera-tional temperature range of the system. Thecatalogs for many pipe manufacturers list therange of properties for various laminates, butvery few provide performance data at elevatedtemperatures. The equation, which is used todetermine the design aspects of any structuralsystem, utilizes factors for the mechanical prop-erties under the expected design conditions,including temperature. Without this informa-tion, the designer is severely handicapped.

Many piping catalogs include tables that thedesigner can use to determine support, guide,and hanger spacing. The spacings are usuallybased on a specific gravity of 1.2, a liquidtemperature of 160 or 180 8F, and a limiteddeflection of 1/2º. This information is usefulfor estimating but in most instances the spa-cings are not based on total pipe stress. Veryseldom is pressure stress considered in the deri-vation of these tables. In FRP piping systems itis very important that the total stress be con-sidered when selecting support spans. By usingthe equations presented in Section 6.31.3.2.6,the designer can accurately define support andguide spacings and be assured that the pipe isdesigned to operate within the specified allow-able stress.

The use of the procedures outlined in thissection will greatly improve the reliability andservice life of any FRP piping system. The sameprocedures will work equally well with ductsystems. As these procedures were being devel-oped it became evident that there were nocommercially available standard supports forFRP piping. Many different designs were illu-strated in many of the catalogs but a review ofthe designs indicated that additional workwould be needed to make them acceptable forFRP piping and ducting. A family of specialFRP pipe support designs is illustrated in Fig-ure 13. This family of supports has been used inalmost every environment and in almost everycondition found in process industries. The ap-plications need to be carefully checked to insurethat loads are compatible but the basic designcan be extended to include pipe diameters up to120º.

When specifying the supports, the designerwill become familiar with the unique featuresthat are important to the design of an FRPsystem. The long support with a fully bondedliner eliminates failures due to local stresses.


The low profile of supports keeps the pipe closeto the structural steel, thus reducing the size andamount of auxiliary steel. Selecting standardsgreatly reduces design time and the standardi-zation of supports reduces manufacturingcosts. Interchangeability and standardizationreduces or eliminates field rework, thereby re-ducing construction costs. Each support shouldbe clearly marked to identify type and location.

Duct systems can be supported using thesesame basic designs, however, since duct systemsvery seldom have fluid loads, the supports canbe much lighter.

Figure 3 shows the change in modulus atelevated temperatures for two filament-woundpolyester pipes. This type of data is required insystem analysis if the design is to be sound.

6.31.3.2.5 Comparisons

The following sections compare and contrastthe design features and advantages of the threetypes of FRP pipe.

(i) Contact molded

The high resin to glass fiber ratio of this pipemakes it ideal for highly corrosive fluids. Inorder to meet the strength requirements in thehoop direction, it usually has a thicker wallthan the other types of pipe. For this reason,it is heavier. Also, since it is virtually hand-made, it is more expensive. Strength in theaxial direction is higher than filament woundpipe. Because the pipe is hand-made, it is sub-ject to wider manufacturing tolerances thanother types of pipe. This is especially important

to the support designer who is responsible forthe designed fit of supports. Contact moldedpipe is highly recommended for use where itmight be subject to a severe exterior environ-ment. Fittings are normally joined to the pipeusing the butt and strap method.

(ii) Filament wound

A high glass content and precise fiber orien-tation make this type of pipe ideal for pressureapplications. Machines are used more in itsfabrication so the tolerances are closer, themechanical properties more consistent, andthe production cost is lower than for contactmolded pipe. Due to the low resin to glass fiberratio, a corrosion liner of a minimum 100 milsshould be provided. Since the axial strength offilament wound pipe is less than that for con-tact molded pipe, at the same pressure rating,the filament wound pipe will require a muchcloser support spacing. This is due to the thin-ner wall common with filament wound pipe.The preferred method of joining fittings andpipe is 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 between thebell and spigot.

(iii) Centrifugally cast

This type of pipe is almost fully machinemade and it provides the most consistent me-chanical properties and the closest tolerances. Ithas a lower glass fiber content than filamentwound pipe and features higher corrosion re-sistance. The smooth outside diameter also fa-cilitates a more consistent support design. Castpipe, due to fiber orientation and higher glasscontent, has a higher axial strength than eitherthe filament wound or contact molded pipe.Cast pipe has an unreinforced corrosion liner,which is susceptible to damage by impact, but ifthe pipe is properly handled and supported, itshould pose no problems. Fittings are normallyof the socket weld type that can be over-wrapped if added joint security is desired. How-ever, with correct installation procedures andinspection, the overwrap is generally consideredunnecessary.

6.31.3.2.6 Design approach

Contact molded FRP pipe, made accordingto PS 15-69 (1969), is normally rated by pres-sure in increments of 25 psi up to 150 psi. Stan-

Figure 3 Tensile modulus, E1, vs. temperature(8F).


dard machine made pipe does not follow thistype of rating and the designers should refer tothe ultimate pressure rating listed in the manu-facturer's catalog. It is important to note thatthese ratings are based on the allowable pressureof a continuously supported pipe subject to pres-sure stress only. Since piping systems are almostnever continuously supported, the stresses ofbending must be considered when determiningthe allowable working pressure of an FRP pipe.The equations presented in Section 6.31.3.3take these stresses into account.

Wall thickness is based on a 10:1 safety factorin the hoop direction and it is customary to usea 5:1 or 6:1 safely factor in the axial direction.By maintaining these safety factors in the de-sign, stress risers in elbows and other fittingswill be within the allowable stress limit.

The method of design layout preferred bymany engineering firms is an anchor to anchordesign. This design method can be economicaland offers many advantages. The anchor toanchor system is more rigid and less susceptibleto damage due to dynamic loading. This systemalso provides a means for controlling expansion(thermal and pressure), thereby reducing thelength of offsets and eliminating the need forexpansion joints. Anchors are placed on eitherside of every change in pipe direction and asnear to the fitting as possible. The amount ofstructural steel required to absorb the loads

imposed on the anchors (see Figure 4) can beminimized by keeping the pipe elevation closeto the steel and by utilizing tension membersbetween anchors. It is important to recognizethat the pipe must be guided between anchorsto prevent buckling. In cases where there arelong straight runs, anchors should be placed nomore than 150±200 feet apart.

In many cases where the anchor to anchordesign is not used, the pipe is often simply hungwith rod hangers (see Figures 5±7). This is anexample of a highly flexible piping system.Expansion is uncontrolled and dynamic forcescan cause very large movements of the pipesystem. This design will work where the operat-ing temperature is near ambient temperatureand fluid velocities are very low. However,even mild fluid dynamic forces can destroy apumped system that is installed in this manner.Vibrations induced by the pump can damagesections of the system where frequencies arewithin the resonant range. Wind loads canalso induce damaging stresses. To reduce vibra-tion and wind load effects, the pipe should belaterally restrained at specified intervals alongthe pipe. These restraints should not be locatednear changes in direction where offset legs arerequired for flexibility.

Many piping system failures that occurduring hydrotesting, or even after years of ser-vice, have been attributed to poor workman-

Figure 4 Anchor loads.


Figure 5 Support spans.

Figure 6 Offsets.


ship. In reality, failures are caused by overstressand this could be due to poor workmanshipand/or unsatisfactory design. The task of thedesigner is to eliminate, as much as possible, thelikelihood of failure. With sufficient effortspent on the design and in the instruction ofinstallation personnel, failures can be effecre-duced.

The design techniques presented here havehelped to standardize a conservative designapproach. Beyond this, a great deal of work isnecessary to standardize installation techni-ques, especially the methods for fabricatingjoints.

In an effort to reduce the possibility of fail-ure, the designer should seriously consider thefollowing:

(i) Keep the pipe run away from high trafficareas where damage from equipment impact islikely.

(ii) Keep flange joints to a minimum.Flanges are expensive components and sourcesof leaks.

(iii) Provide vents at each high point to allowair to be removed from the system prior totesting and system start up.

(iv) Provide drains at each low point orpocket. Drains with blind flanges will allowthe line to be drained if repairs are necessary.

(v) Ensure that all supports, anchors, and

guides are installed prior to the hydrotest.This cannot be overemphasized since the pipesystem can be severely damaged without properpipe support.

(vi) All valves and valve operators or com-ponents in the system must be independentlysupported.

(vii) Valves that require high torque to openand close should be anchored so that the hightorque does not damage the pipe.

(viii) Riser supports for vertical runs shouldbe guided or laterally restrained to reducevibration and effects of wind load.

6.31.3.2.7 Hydrostatic testing

When filling the system for hydrostatic test-ing, all high point vents should be opened toallow air to be vented. Fill the system at thelowest point and connect a small, positive dis-placement pump with a maximum flow rate of3±5 gpm. The pump should be equipped with apressure regulator and bypass that will allowthe system pressure to build slowly.

Hold pressure at 25, 50, 75, 100, and 120% ofthe design pressure. The hold time at each levelshould allow sufficient time for checking forleaks. Any leaking flanges will require retor-quing of bolts. Bleed off all pressure before

Figure 7 Guide spacing.


retorquing. Increase torque to 110% of initialrecommended value and retest the system. Ifthe flanges continue to leak, bleed of pressureand increase torque to 120%. If the flangescontinue to leak, drain the system and inspectthe flange faces and examine the gasket fordamage. Never retorque bolts when the systemis under pressure.

6.31.3.2.8 Economic considerations

With material prices and the cost of laborrising frequently, a cost comparison between anFRP system and any other corrosion resistantmaterials is difficult. FRP is normally selectedbecause of its corrosion resistance, however,one important point that should be made con-cerning any comparison is that the total in-stalled cost be considered. Many studies donot include data on the support system requiredfor FRP pipe. This is because most analysisprocedures tend to regard all piping systemsas being supported in the same manner and atthe same relative cost. In addition, the cost ofauxiliary steel, and the labor necessary to installthat steel, should be evaluated.

The service life of each system is an impor-tant factor and should be included in the eva-luation if sufficient historical data can beobtained. Many designers would probablyelect to use materials other than FRP whenthe installed price of the two systems is rela-tively close, but the extended service life of FRPsystems will usually be more favorable. Gener-ally, experience has indicated that FRP systemsare more economical than other systems in pipesizes above 4º where special metallic materialsare considered.

6.31.3.2.9 Applicable codes and standards

There are very few codes or standards applic-able to the design of FRP piping systems. Thedesigner should be familiar with the AmericanNational Standard Code for Pressure Piping(ANSI) B31.3; although it deals mainly withmetallic pipe it has been expanded to covernonmetallics including thermoplastic and ther-moset materials. The only other standard thatcould prove useful for design purposes is theNBS Voluntary Product Standard PS 15-69(1969), which covers custom contact moldedFRP equipment. This document is no longerpublished by NBS but copies can be obtainedthrough some of the resin and glass manufac-turers. The tables for pipe included in thisstandard should be used with care.

The American Society for Testing and Ma-terials (ASTM) has published standards for

Plastic Pipe and Building Products, Section 8,Volume 08.04 (1993). This document is a com-pilation of test procedures and methods forestablishing material and mechanical propertiesfor plastics used in piping.

A number of codes and standards are beingdeveloped to promote standardization of theproduct, but they are not available at thistime. One excellent guide that is available is abook by Mallinson (1988). Another book thatprovides good overall coverage of the use ofFRP is by N.P. Cheremisinoff and P.N. Cher-emisinoff (1978).

The Composites Institute of the Society ofPlastics Industry published a Fiberglass PipeHandbook in 1989 that is a document writtenby the Fiberglass Pipe Institute, New York.The handbook is a compilation of technicalsections covering above and below groundpiping systems and while it is an excellentreference for piping design, the methods ofanalysis and design of supports presented inthis book are not the same as recommended inthis section. Expansion joints and expansionloops are very rarely used in practice and thesupports recommended in the handbookshould not be used except in very light dutyservice.

6.31.3.2.10 Layout and design of pipingsystems

The preliminary piping layout for FRP pip-ing is the same as for any other system(Figure 8). Once a general piping arrangementhas been selected, an isometric of the systemshould be made and the following steps taken.

(i) Locate available support steel and estab-lish the location of additional support steel asrequired. Existing bridges, pipe racks, andbuilding structural steel will establish the avail-able support spacing.

(ii) Locate anchors at each change in pipedirection and as close as possible to elbows.

(iii) Locate riser supports and componentsupports. Riser supports can be tentativelylocated on 10-foot centers until calculationsare made.

(iv) Establish support design criteria andpipe wall thickness required using the equationsin Figures 3±7 factoring the operating tempera-ture and pressure of the system. An iterativeprocess is employed to obtain wall thicknessand to define acceptable support spans.

(v) Tabulate support design criteria shownin Table 2 and rearrange support spacing andanchor locations on the isometric to meetdesign criteria. Add guides at locations deter-mined in the table.


(vi) Check offset leg requirements betweenanchors at directional changes. Relocateanchors as required to meet offset require-ments.

(vii) Rearrange riser support locations. Thedistance between centers should not exceed theguide spacing. In areas where offset leg require-ments cannot be met, consideration should begiven to rerouting the pipe to provide moreflexibility.

6.31.3.2.11 Vibration, water hammer, andcavitation

(i) Vibration

Pump or equipment vibrations are usuallyabsorbed by an FRP piping system with littleeffect; however, it is an accepted practice by

some engineers to use an expansion joint at thepump discharge. If the piping cannot be an-chored the expansion joint must be restrainedwith tie rods. The use of an expansion joint mayallow thrust loads to be imposed on the pumpand care must be exercised to insure that thepump is capable of handling the thrust loadsand/or thermal loads that are developed by thepiping system.

It is sometimes possible to have segments of apiping system that are subjected to vibrationsthat result in large deflections of the piping.This usually occurs when segments are notsupported or guided. Severe damage canoccur during start up or shut down if the pipeis subjected to frequencies at or near the naturalfrequency of the pipe. The natural frequenciesof several pipe sizes are shown as a function ofsupport span in Figure 9. The forcing frequen-cies generated by a pump are normally muchhigher than the natural frequencies of the pipe

Table 2 Sample calculations

Nominalpipe size

Wallthickness

(in.)

Supportspan

(Max.)

Offsetleg

(Min.)

Guidespacing(Min.)

Anchor load(Max.)

4 0.202 8.3 0.47��Lp

11.5 35006 0.202 9.6 0.64

��Lp

16.7 520010 0.250 12.3 0.82

��Lp

28.0 984212 0.265 13.1 0.90

��Lp

33.7 12250

Figure 8 Typical pipe run (after Britt and Britt, 1993).


but transient frequencies during start and stopcan produce high deflections and high stresses.Figure 9 can be used to approximate therequired spacing to insure that dynamic condi-tions cannot damage the pipe.

(ii) Water hammer

Water hammer in a piping system is causedby high-energy fluid transients and is easilyidentified by the sound that can be comparedto the sound of a series of hammer blows to thepipe (see Figure 10). The magnitude of thetransient is a function of the fluid properties,change in velocity, and modulus of elasticity of

the pipe. The transient condition results in apressure wave that can produce a shock thatmay exceed five times the normal system pres-sure (see Figure 10).

(a) Calculation of pressure rise. Considera fluid flowing frictionless in a rigid pipe ofuniform area A with a velocity V. The pipehas a length L, and an inlet pressure p1 and apressure at the outlet of p2 at L. At length L,there is a valve which can suddenly reduce thevelocity at L to V±DV. The equivalent massrate of flow of a pressure wave traveling atsonic velocity c, M= rAc. From the impulse-momentum equation, M(V27V1)= p2Ap1A1;for this application (rAc)(V7DV7V)=p2A7 p1A, or the increase in pressureDp=7rcV. When the fluid is flowing in anelastic pipe, such as in an FRP pipe, the equa-tion must be modified to account for the ex-pansion of the pipe; thus

c ��

Es

P�1� �Es=Ep��Do �Di�=�Do ÿDi��

s�1�

where r=mass density of the fluid, Es isthe bulk modulus of elasticity of the fluid, Ep

is the axial modulus of elasticity of the pipe, Do

is the outside diameter of the pipe, and Di isthe the inside diameter of the pipe.

In many cases the piping system can be sub-jected to large movements which can causesevere overstress. The cause of the hammer isa very rapid change in fluid velocity as a resultof a quick closing valve or a rapid start or shutdown of a pump. The best way to reduce theshock due to valve opening is to slow the open-ing and closure of the valve. Air or hydraulicactuated valves can be programmed to openmore slowly by restricting the actuation pres-sure. A needle valve installed in either the inletor outlet side of the actuator provides a simple

Figure 9 Natural frequency vs. support span (afterBritt and Clark, 1996).

Figure 10 The build up of shock waves by quickly closing a valve at the end of a line.


way to reduce operating speeds. Experience hasindicated that by restricting the opening andclosing to approximately 10±20 s, most pressuresurges can be eliminated.

(b) Time of closure. These calculationswill provide the engineer with an approxima-tion of the severity of the pressure wave and theclosure time for the valve can be established toattenuate or eliminate the shock. The time for apressure wave to travel the length of a pipe Land return is t=2L/c. If the time of closure tc isequal to or less than t, the approximate pressurerise

p=72rV(L/t c) (2)

Typical values for fluid and material propertiesare r=1.937 lb-s2/ft4 for water, Es=319 000lb/in2, Ep=1.06 106 lb/in2 axial modulus forFRP pipe; and c=4860 ft/s.

When the system shocks cannot be controlledor eliminated by slowing the valve closure,other means of attenuation must be employed.Air chambers, surge tanks, expansion joints,and standpipes are a few of such devices thathave been used for this purpose. These areexpensive and have disadvantages such aslimited life, excessive maintenance, or they

may not cover the full range of pressures.Each of these devices requires special engineer-ing and should be carefully reviewed by themanufacturer of the device. Many piping sys-tems carry process fluids containing solids ormay be corrosive. The operation of the devicemust not be affected by a build up of solids orcorrosion. Two typical devices are illustrated inFigures 11 and 12.

The pump start up can be a problem, espe-cially if the line is empty when the pump starts.A full line is important and if the dischargevalve is properly timed there is usually verylittle shock. The main problem occurs whenthere is a power failure resulting in a quickrundown of the pump. This can cause a vacuumto be formed in the pipe and can result in aphenomenon called water column separation.This occurs in long lines where the momentumof the fluid column causes a vacuum to beformed at the pump discharge or at a pointjust downstream of the pump. As the fluidcolumn slows and stops there is a reversal offlow and when the two columns collide at thepoint of separation there is a large pressure riseat the point of collision. Whenever this condi-tion occurs, normal water hammer solutionsare no longer valid. Whenever possible, watercolumn separation should be avoided becauseof the potentially high-pressure rises and thevacuum conditions which can cause pipe fail-ure. Water column separation presents a verydifficult problem for analysis. One method ofsolving this problem is presented in a paper byKephart and Davis (1961).

Figure 11 Cross-sectional view of a gas filledpulsation dampener.

Figure 12 Pulsation damper


Water hammer can be a serious enemy ofFRP piping systems but a properly supportedand anchored piping system can safely handleall but the most severe shock conditions. Ifcontinual shock problems persist, the sourceand cause of the hammer should be determinedand corrected.

(i) Cavitation

This is caused by a restriction in the line, suchas a control valve, that causes a drop in localpressure due to high flow velocities through therestriction. Cavitation will eventually erode thecorrosion barrier and in time, damage the struc-tural wall of the pipe. The effects of cavitationare usually limited to a short section of pipe justdownstream of the restriction and can be de-tected by a noise that sounds like gravel beingpumped through the line. Gate valves havemuch better flow characteristics than butterflyvalves and should be used whenever possible. Avery popular and successful solution to cavi-tation can be achieved by continuously intro-ducing a small continuous flow of air into thepiping system just upstream of the valve or con-striction. Large diameter systems may requireair injection at several points around the pipe.

Cavitation usually occurs when a small valveis used to control flow in a line size that is 2±3times the size of the valve size. The small valveis selected because of cost or because the con-trol range is narrow and the smaller valve iseasier to control. Some engineers have installedtwo valves in series with a short spool betweenthe valves to reduce the local drop across eachvalve. This is an expensive solution but willwork when the process will not allow air to bebled into the system.

6.31.3.2.12 General

The design approach presented in this sectionhas been successfully used for over 20 years andwill provide the engineer and designer withanalytical tools and procedures that will insurea successful piping system if reasonable careand control is exercised when the pipe is in-stalled. The supports, guides, and anchors thatare illustrated have been designed to match theanalysis and support requirements for FRPpipe and will provide maximum service life forany FRP system. The designer is again cau-tioned to specify the finish and/or coating forthe support to prevent or reduce corrosion ofthe supports. Standard finishes for most condi-tions are either epoxy primer or hot dip galva-nize. Special coatings must be specified forextreme corrosion conditions and suppliers of

these materials should be consulted for recom-mendations and specifications.

There is a wide selection of materials, meth-ods of manufacture, pipe grades, and ratingsavailable to the engineer when specifying FRPpipe. Generally the hand lay-up pipe is specifiedfor extreme conditions, especially where exter-nal corrosion might be expected. While thispipe has a lower hoop strength, the higheraxial strength provides better beam strength.The method of fabrication allows this type ofpipe to act more like an isotropic composite.

When the designer is considering the use ofthe more economical filament wound pipe he/she should consult the manufacturer's catalogdata for mechanical properties. It is often as-sumed that the axial strength of the filamentwound pipe is the same as the hoop strength;this is a dangerous assumption. The axialstrength of this pipe varies between 9000 and11 000 psi. It is common practice to use 9000 psifor all calculations.

The cast pipe offers some unique mechanicalproperties due to the nature of construction.Hoop and axial strengths are as high as25 000 psi providing excellent mechanical prop-erties for maintaining longer spans.

Selecting the method of joining pipe sectionsand fittings is an important consideration forthe designer and while joint strength is a criticalissue, the joint quality will always dictate thesuccess of the piping system. There are threebasic methods being used today, not countingthe bolted flanged connection, which must beconsidered. The most widely accepted methodis the butt and strap joint. In its simplest form,two pipe ends are butted together and over-wapped around the outer circumference of thepipe. This has been called the workhorse of allconnections and is the easiest to fabricate andinspect for quality. The outer wrap shrinks as itcures and provides a strong mechanical bond.Each step of the lay-up is performed in openview and any discrepancies are easily detectedand corrected before the joint is complete.

Some pipe, especially the commodity type, isnormally joined by means of a bell and spigotjoint. The spigot end of the pipe is coated withan adhesive and inserted into the bell. Some-times the bell and spigot is tapered rather thanstraight. Both of these joints are satisfactorywhen assembled by a skilled craftsman. Apply-ing an even and smooth coating of adhesive isimportant as well as insuring that the spigot isinserted completely into the bell. Keeping thepipe rigid as the adhesive cures is critical as anymovement can ruin the joint. The tapered jointadds a bit more difficulty and does not seem tooffer any great structural advantage over thestraight bell and spigot. After the joint has been


completed there is no way to determine if thejoint was properly made. The proof of the jointis not determined until the entire system ispressurized. Repairing discrepant joints at thispoint is very expensive.

In most critical process systems it is wise toselect an engineered (custom) pipe and to usethe Butt and Strap joint for most connections.Flanges should be kept to a minimum.

The most important factor in insuring a rea-sonable service life is the consideration of awell-designed support system. The designercan contribute to the success by routing thepipe through areas where access to structure isavailable for supporting the pipe.Many systemsare compromised when the designer attempts toshorten the routing by using diagonal routes tosave a few feet of pipe. The 45-degree fittingswith diagonal runs are difficult to analyze andpose awkward support problems. The engineerand the designer need to work closely togetherduring the preliminary pipe design in order toreduce support and structural costs.

Maintenance is a matter of paramount im-portance when designing the system. Keepclearances between pipes and between struc-tures large enough to make joint repairs.Make sure that FRP pipe is never allowed torub or contact sharp edges during operation.Abrasion and impact damage can drasticallyshorten the life.

With all of the advantages that FRP can offerin handling corrosive fluids, it is easy to see whythe designer and engineer might prefer thesematerials, and when the principles of designare carefully followed there is no other cost-effective competitor. But when the wrong resinor type of construction is selected, or when thedesigner neglects to properly design the re-quired supports, these materials can pose ser-ious problems and cause the owner doubts as towhether there is a real advantage. The designprinciples in this section were developed forFRP pipe and have proven that failures canbe virtually eliminated when put into practice.

6.31.3.3 Approaches for Design of Supports

The designer should review the following de-sign considerations to insure that all supportsare correctly used. If there are any deviationsfrom these standard practices and designs, thedesigner should contact the engineer (Britt andBritt, 1993).

6.31.3.3.1 Fitup of support

The designer must specify the maximum out-side diameter (OD) of the FRP pipe to insure

proper support fit. Pipe specifications normallyrequire the pipe manufacturer to maintain atolerance +1/8º, 70.0º on the OD and themanufacturer is required to state the maximumOD in the quotation. The support will be man-ufactured to fit within 1/16º of the maximumOD.

6.31.3.3.2 Location of supports

When supporting pipe inside a building, thebuilding steel will provide the easiest supportpoints. If the support spacing is based on thespacing of the structural steel, and is found toexceed the calculated support spacing, use aslightly (1/16º) thicker pipe wall and re-runspacing calculations. Continue adding wallthickness until the required span is reached oruntil the added wall thickness starts to decreasethe span capability. If the pipe will not meet thespan then intermediate supports, requiring theaddition of auxiliary steel, are required. Ofcourse a comparison of the increased pipe costvs. the cost of auxiliary steel will allow thedesigner to decide whether a heavier pipe willoffer advantages.

6.31.3.3.3 Location of guides

Guides serve as supports and also providelateral restraint to prevent buckling of thepipe due to forced generated by thermal expan-sion. Small diameter piping will require morefrequent guiding and in some cases the use ofguides may be required at every support point.Large piping may require every other supportpoint to be a guide. Calculations should bemade to determine exact requirements.

6.31.3.3.4 Location of anchors

Anchors can be located at each change ofdirection in many applications and allow thesystem to operate at the lowest possible stress.This increases service life and greatly reducesthe susceptibility of failure due to dynamics. Insome cases it may not be possible to fullyanchor portions of the system due to structurallimitations. When this occurs, the amount ofoffset must be determined through the use ofthe offset equation shown in Figure 6.

6.31.3.3.5 Fixing of anchors

FRP anchors are designed to lightly grip thepipe and are never to be allowed to clamp thepipe with any excessive force. The anchor isfixed to the pipe by applying shear collars or


FRP bands to the pipe on either side of theanchor. Except for very unusual cases the col-lars are applied in the field after the anchor hasbeen installed. The collars are built up of layersof 1.5 oz. mat to a thickness that allows theanchor to bear against the collar (seeFigure 13.21).

6.31.3.3.6 Riser supports

Vertical runs of pipe inside a building arenormally supported on floor sleeves or off ofcurbs surrounding a pipe chase through thefloor. Riser supports or riser guides when re-quired are fixed to the pipe using the same shearcollars used with anchors, however, the collarneed only be applied to the top side of thesupport so that the weight of the riser can becarried by the riser support. The rule for riserguide spacing is the same as other guides unlessthe pipe is subjected to wind loads where morefrequent guiding is required. It is important tonote that loads for riser supports can be veryhigh, especially in large diameter pipe. Loads inexcess of support ratings will require specialdesigns and should be brought to the attentionof the engineer.

6.31.3.3.7 Supports for insulated pipe

Special supports are used to accommodateup to 4º of insulation. In all except very specialcases the supports, anchors, and guides areattached to the pipe and are not designed toclamp or support the outside of the insulation.When heat tracing is required the tracing passesoutside of the support. Please note that if heattracing is required, contact an engineer forspecial details and designs.

6.31.3.3.8 Component supports

It is very important that all valves and inlinecomponents be supported independently of thepipe. In some instances it is necessary to anchorthe component where heavy actuators arecantilevered off of the valve or component orwhere external loads or dynamics might da-mage the pipe. Components in vertical andhorizontal pipe runs require support althoughcomponents in vertical runs may not requireindependent support of each component.

6.31.3.3.9 Thermal expansion

The thermal expansion of FRP is 2±3 timesthat of steel and requires special attention espe-cially where a fully anchored system is not used.

Expansion joints and expansion loops aresometimes specified but these add a weaknessto the system. Expansion loops in addition toadding extra piping will add as many as fourfittings and at least eight more joints. Each jointis an additional point of weakness. If lack ofstructural restraint presents a problem whereanchor loads might preclude the use of theanchored system, there are several other designmethods that can be employed, but in mostcases the anchored system can be incorporated.The descriptions of the other design methodsare beyond the scope of this chapter becausethese are special cases.

6.31.3.3.10 Coatings

The standard coating for most support ap-plications is either a high-quality prime coatthat is applied by spray coating, or hot dipgalvanizing. Paint systems must comply withEnvironmental Protection Agency (EPA) regu-lations regarding volatile organic compounds(VOCs) and hazardous materials. It is veryimportant that the designer select a corrosionresistant coating that will withstand the envir-onmental conditions in the area where the pipesupports are to be installed. If special highperformance coatings are required these shouldbe specified in the purchase documents.

6.31.3.4 Support Illustrations

The following illustrations from Britt (1983)present a variety of supports that have beensuccessfully used in conjunction with the designprocedures and practices that have been pre-sented in this section. These support designscover almost any requirement needed in thedesign of an FRP piping system and can beadapted to duct systems by simply making afew design alterations to accommodate thelighter loads imposed by ducting.

Caution is again raised to insure the supporthardware is protected by the proper coating orby galvanizing. The supports shown are pro-duced with a low Durometer rubber linerbonded to the inside of the support to protectthe pipe surface. Roundness and concentricityare key elements of the support specificationand the support diameter should closely matchthe unique diameter of the FRP pipe. Lowclamping forces must be used so that local stressdoes not crush the pipe. Clamping forces shouldnever be used to restrain the pipe. Piping anddynamic forces are transferred to the anchor orriser support by means of a field applied shearcollar. Shear collars are illustrated in Figure 13.


6.31.4 CONCLUDING COMMENTS ANDFUTURE PROJECTIONS

The fiberglass industry was born in the early1950s as an alternate material competing withcoated steel, stainless steel, and other specialtyalloys. FRP began to make inroads into theautomotive industry when FRP bodies wereintroduced at about the same time. Plasticstoday are used in almost every product webuy and use.

This chapter has addressed the use of FRP inindustrial applications where the acceptancehas been much slower. The slow developmentof standards and codes for this unique materialhas been a major impediment to growth but, inthe 1970s, as corrosion became a primary issue,many new applications were attempted with agreat deal of success. Failures were not uncom-mon but as engineering became familiar withthe mechanical properties, design practicesbegan to evolve and with the publication of

Figure 13 Support illustrations (after Britt and Britt, 1993)


case histories, codes and standards began to bedeveloped.

Today corrosion problems plague the chemi-cal process industry, costing this industry morethan $82 billion a year. Studies have indicatedthat more than one-half of this cost could besaved through the use of FRP in plant design.Corrosion has spurred a rapid growth in the useof these materials but recent US environmentallegislation, CFR 40, Resource Conservationand Reclamation Act (RCRA) and EPA man-

dates for clean air and water will greatly in-crease the demand for FRP piping, tanks, andducting.

In the US a recent market survey (Britt, 1998)has indicated that the industrial market (pulpand paper, chemical, and power industries) forthe next five years in just the environmentalapplications will exceed $1.6 billion per year.A great deal of work is underway to developnew guidelines, specifications, codes, and stan-dards and as these are put into the hands of the

Figure 13 (continued)

Concluding Comments and Future Projections 23

engineers the growth of the FRP industry willbe based on a solid foundation.

The rising cost of oil presents an economicdeterrent to the growth of the FRP market andit is having an effect as the cost of this materialapproaches or exceeds the cost of such materi-als as stainless steel, titanium, and special steelalloys. It is important to improve competitive

difference and this can be achieved by engineer-ing. Design factors can be reduced as engineersbecome more confident of the mechanical prop-erties of this material. This is being accom-plished through testing and improvedanalytical tools, and will be a factor in reducingequipment costs. Efficient designs will help fuelthe demand for new applications.

Figure 13 (continued)


6.31.5 REFERENCES

`API Standard 650 Welded Steel Storage Tanks for OilStorage', American Petroleum Institute, Washington,DC.

ASME RTP- 1, `Reinforced Thermoset Plastic CorrosionResistant Equipment', The American Society of Me-chanical Engineers, New York, 1993.

ASME B31.3, `Chemical Plant and Petroleum RefineryPiping', The American Society of Mechanical Engi-neers, New York.

ASTM, `Plastic Pipe and Building Products', AmericanSociety for Testing and Materials, Philadelphia, PA,vol. 08.04.

ASTM D2996, `Standard Specification for FilamentWound Reinforced Thermosetting Resin Pipe', Amer-ican Society for Testing and Materials, Philadelphia,PA.

ASTM D2997, `Standard Specification for CentrifugallyCast ReinforcedThermosetting Resin Pipe', AmericanSociety for Testing and Materials, Philadelphia, PA.

ASTM D 3299, `Standard Specification for Filament-Wound Glass-Fiber Reinforced Thermoset Resin Che-mical-Resistant Tanks', American Society for Testingand Materials, Philadelphia, PA.

ASTM D 4097, `Standard Specification for Contact-Molded Glass-Fiber Reinforced Thermoset Resin Che-mical-Resistant Tanks', American Society for Testingand Materials, Philadelphia, PA.

F. Britt, in `Business Projections for Fiberglass ReinforcedPlastics, FRP Symposium', Niagara Frontier Section ofthe National Association of Corrosion Engineers Inter-national (NACE), Buffalo, NY, 1998.

F. Britt and C. K. Clark, Basic Requirements for Ship-ping FRP Equipment, Clark, Ph.D., National Associa-tion of Corrosion Engineers, Frontier Conference,Buffalo, NY, 1996.

W. F. Britt, Jr., `Design Consideration for FRP PipingSystems', Managing Corrosion with Plastics, NationalAssociation of Corrosion Engineers, Houston, TX,1979, vol. IV.

W. F. Britt, Jr., in `Providing Proper Supports for Re-

inforced Thermoset and Non-Reinforced ThermoplasticProcess Pipe', The National Association of CorrosionEngineers, Paper No. 92, The International CorrosionForum by the National Association of Corrosion En-gineers, Anaheim, CA, April 1983.

W. F. Britt and W. F. Britt, Jr., `FRP Piping DesignManual', Britt Engineering Inc., Birmingham, AL,1993.

N. P. Cheremisinoff and P. N. Cheremisinoff, `FiberglassReinforced Plastics Deskbook', Ann Arbor Science,Ann Arbor, MI, 1978.

G. A. Escher, `Transition to FRP, Basic Guidelines forPiping Designers and Users', Managing Corrosion withPlastics, National Association of Corrosion Engineers,Houston, TX, 1979, vol. 4.

Fiberglass Pipe Institute, Fiberglass Pipe Handbook, TheComposites Institute of the Society of Plastics Industry,New York, 1989.

J. T. Kephart and K. Davis, Trans. ASME J., 1961,September, 334±342.

J. Mallinson, `Corrosion-Resistant Plastic Composites inChemical Plant Design', Marcel Dekker Inc., NewYork, 1988.

Mark's Handbook for Mechanical Engineers, McGraw-Hill, New York, 1996.

E. Megyesy, `Pressure Vessel Handbook', Pressure VesselPublishing, Tulsa, OK, 1995.

M. L. Nayyar, `Piping Handbook', 6th edn, McGraw-Hill, New York, 1992.

NBS Voluntary Product Standard PS 15-69, CustomContact-Molded Reinforced Polyester Chemical Resis-tant Process Equipment, 1969.

Pulsation Preventor, Pulse Guard, Inc., PO Box 506,Hampstead, NC 28 443, USA.

Pump Handbook, 2nd edn., McGraw-Hill, New York,1995.

J. H. Smith, `Fluid Energy ControlÐSome Causes andSome Controls of Hydraulic Transients in Piping Sys-tems, Managing Corrosion with Plastics', NationalAssociation of Corrosion Engineers, Houston, TX,1979, vol. 4.

References 25

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