The Successful Application of FRP Linings in Above-Ground Storage Tanks: A 20-Year History by Louis C. Sumbry, ‘Amoco Corporation; and Robert M. Trull and Jacqueline Klass, Amoco Chemical Company rmoco has identified fiberlassreinforced plastic (FRP) lining as the most cost- ‘effetve solution to internal corrosion of above {round steel storage tank bottoms. From ts long history of using FRP linings in above-ground storage tanks, the company has developed an internal standard to ensure proper material seletion and installation techniques. Isophthalc acid-based, unsaturated polyester, offering excellent corrosion resistance ata ‘moderate price, was chosen asthe most cost effective resin. Other material selection included specifying the type and level of reinforcements, ‘The proper instalation method was also specified to standardize surface preparation, installation, and inspection Recent intemal surveys indicate that many of the original linings are sil in service after 20 ‘years of continuous use. Background Problems with Intemnal Tank Bottoms Steel tanks are designed to lst 20 to 30 years; however, if the bottoms are not properly protected from corrosion, they may have tobe replaced after only 5 years. Typically, thin film (15 to 30, ‘mils [380 to 750 microns} dry film thickness) coatings such as amine epoxy, coal tar epoxy, or pony phenolic are used on new internal tank bottoms to protect steel against internal corrosion. Thin film coatings, however, ae not suitable for use over heavily pitted and thinned internal tank bottoms. In these situations, FRP linings are required, An FRP lining system provides protection against corrosion from the stored product and structural reinforcement for steel bottoms exposed to corrosion by the external environment History of the Use of Coatings for Lining Internal Tank Bottoms ‘The use of reinforced or filled coatings in petroleum tank bottoms is not new. Heavy, sand- filled bitumen coatings have been used for many years, especially in crude oil tanks, to prevent in- ternal corrosion by corrosive oils and bottom sedi ‘ment and water. Protective coatings such as coal tar epoxies and epoxy phenolics were first used in the 1950s, and later in the 1960s, epoxies and polyesters replaced the sand-filed bitumen coatings. ‘At that time, FRP ining systems were used to,epair reinforce, and thus extend the life of steel bottoms exposed primarily to external corrosion. ‘Today, however, FRP lining systems have proven an acceptable, cost-effective alternative to replacing ‘corroded ste! bottoms, whether the source of cor rosion is internal (ie, from the product contained within the tank) or external (ie, from expasure to contaminants from the sol). Prior to the application of a protective lin- ing, small holes or thin areas in the corroded tank bottom are patched with heavy layers of resin rein- forced with glass cloth, glass mat, glass roving, or metal sets. For repair and reinforcement, the ‘physical properties of isophthalic polyester and bisphenol epony resins provide the greatest resis- tance to chemicals and solvents, Such resins are ‘most easly applied by the hand lay-up method, and ‘most effective when reinforced with 2-1/2 o per sq ft (700g/sq m) of glass mat or glass roving applied toa total dry film thickness of 60 to 150 mils (1.8 ‘mm to.45 mm) (Fig, 1, 40 | Journal of Protective Coatings & Liningswere used to inject air and garnet grit into the pipeline to blast the inside of the pipe. Grit was propelled through 1 end of the pipeline: dust collectors placed at the other end were used to contain the spent abra- sive and dust. A two-mil (50-mieron) pro- file was specified by the Navy. Profile was monitored using replica tape. At the front and back of each pipe section, an impres: sion of the profile was taken with the tape and measured witha spring micrometer. The lining procedure was similar to the cleaning process and was performed almost simultaneously with cleaning, After 1 see- tion was cleaned, it was lined, again using 4, 1600-CFM air compressors to propel the lining. Excess paint was collected in a ve covery vessel attached hy hose to the back end of each pipe section. Workers then moved on to clean and line the next sec: tion. Two coats were needed to ensure the required 12-mil (¢ 3 mils) [300 £75 mi: rons}, holiday-free dry film thickness, so after each section was lined once and cured for a maximum of 24 hours, workers ap- plied a second enat ofthe epoxy in the same ‘The second coat cured for 72 hours be- fore the pipeline was returned to service AA borescope was used at both ends of each pipe section to allow inspectors to verify visually that the inside of each sec- tion of pipe, including elbows, was lined, according to Wayne Nishimoto of American Pipeline Co. ‘The first installations of the pipe lining cost about $280,000 per carrier; this amount is expected to be reduced with ex: perience, Brady says. The lining is expected to last a minimum of 6 years, according to Brady and Mori. Its important to note, says Brady, that this process is suitable for cathodic metals ‘only and must not be used on anodic met- als such as iron alloys. This caution is an added measure to ensure successful appl cation. Should there be pinholes or defects in the first layer of lining applied to a sec tion of pipe, the exposed metal will not be damaged because cathodic metals are not reactive. However, anodic metals, when ex- posed, lose electrons and suifer rapid metal loss, leading to rapid pitting and perfora- News from the Field contin tion ofthe pipe section. Tes hoped that this process willbe used for drinking water pipes, which are also made from copper nickel. The ingredients chosen forthe lining have previously been approved for contact with potable water. The paint contains no volatile solvents, and the cured paint contains no extractable ‘materials. The Naval Medical Command is reviewing the formulation of the lining for possible approval fr application to drink ing water pipes. Michael Gustavson isthe engineer in change ofthis work. Brady directed formu lation ofthe lining at NRL. Jefirey Breiden- stein of Geocenters, In. (Fort Washington, MD) and Dr. James D. Adkins of SachsPreeman Associates, In. (Landover, MD) helped develop and test the lining, Funds from the Naval Sea Systems Com- ‘mand Detachment PERCY (Planning and Engineering for Repairs and Alterations— Carriers) in Bremerton, WA supported ‘work to develop the lining From Dr. Robert Brody, Naval Research Laboratory; and American Pipelining CoFRP Linings The Effect of Material Selection on Performance ‘Testing of Resin Systems Because ofthe problem ofboth internal and exter- nal corrosion, the resin used asa tank ining must demonstrate suficient corrosion resistance to en- sure long term durability of the laminate and to rmiimize the rsko leakage. To determine which resin type should be use, researchers conducted a series of studies to evaluate the corrosion ress- tance of fiberglass-einfrced resin panels. One- sied (ASTM C 868, “Test Method for Chemical Re sistance of Protective Linings’ and two-sided {ASTM C581, “Practice for Determining Chemical Resistance of Thermosetting Resins Used in Glass Fiber Reinforced Structures Intended for Liquid Services" test methods were used to examine 5 diferent resin types: isphenok-Aepon, bisphenol A polyester, isophthalic polyester, orthophthalic polyester and vin ester Standard ASTM C 581 laminates were con- structed using the above resin systems. These pan- «els were then exposed to a variety of chemical media, including benzene, distilled water, 5 per cent acetic acid, 5 percent nitric acid, 5 percent sodium hydroxide, and 5 percent sulfuric acid. ‘The one-sided exposure tests were conduct- ed using Atlas Cells (per ASTM C 868). The Alas Cell consist ofa horizontal short glass cylinder with’3 necks on the upper half ofthe ender. Two steel panes, 8 in. x8 i. x 0.25 in, (20 emx20 em 10.6 cm), coated on one side with a lining system ate clamped, one panel on each side, onthe open ends of the horizontal cylinder? ‘The lined side ofeach test panel is exposed to the test solution. The panels were evaluated after3 months, 6 mons, and 12 months. The evaluation consisted ofthe following: adhesion (ASTM D 3359), hardness (ASTM D 2583), and vi- sual appearances. ‘The two-sided exposure followed the ASTM C581 test method, Standard ASTM C 581 fiber- slass-reinforced panels were fly immersed inthe Yarious chemical media fra period up toa year. At intervals of 1 month, 3 months, 6 months, and 1 year of exposure, the leural properties and hard- ness ofthe panels were measured. After being plot. ted on the log-log sal, the data could be extrapo: lated out to 10 years to predict the long-term performance of each resin system, To be consid- ered acceptable, a material must retain a minimum Cross-section oflaminate 26. 95002 m0) aca coo e.3mm aap 25006 400g hs mat 2s 005m) awe me) Cost ton of he lminate Courtesy Amoco Corporation ‘of 50 percent of both its flexural properties and hardness. ‘Summary of Resin Resistances ‘Our company’s test results ofthe above resins have been previously reported, The following general characterization ofthe resins tested in our com pany’s laboratories are based onthe retention of, physical properties and visual appearance of the * Bisphenol-A epoxy: This low viscosity amine epony resin has good resistance to mineral acids and outstanding resistance to caustic. This epoxy has fair resistance to benzene and poor resistance to dilute acetic acid * Bisphenol polyester: This bisphenol-A Polyester resin has excellent resistance to all ofthe solutions tested except for benzene, for which it has poor resistance. This generic type of material does well in caustic, * Orthophthalic polyester: This general purpose corthophthalic polyester resin has the least desir able chemical resistance properties for use as an internal tank liner. Its performance in benzene and dilute caustic was poor. In dilute acetic acid and ‘mineral acids, this polyester has fair to good resis- tance « Isophthalic polyester: This isophthalic polyester resin performed well in each ofthe solutions test- ced. This material exhibited no excessive weakness in any of the chemicals or solvents tested. Its per- formance in benzene was only fair, but better than the performance ofthe orthophthalics and the bisphenol-A polyester resins. In caustic, the isoph- thalic polyester didnot perform as well a the March 1980/41FRP Linings 8 ol "o6i 1062 1989 1004 1995 1900 1967 1988 1969 1800 ver rg 2 Historical nts of poster esis (0S) epoxy or the bisphenol-A polyester, but it was far superior tothe orthophthalic resins. Performance inacetic acid andthe dilute mineral acids was very good. « Vinyl ester: The ving ester performed well in all ‘media tested. Vinyl esters perform well in aromatic storage, such as paraxylene. Resin Selection Criteria Suificent corrosion resistance isnot the sole de- termining factor for resin selection. The resin s- tem chosen must cure at room temperature and exhibit good adhesion to the steel tank floor. In ad- dition, the resin must have sufficiently low viscosi- ty toallow for easy wel-out of the glass fibers and removal of entrapped air. Finally, the resin system must be economi- cally reasonable, providing the best performance for the lowest cost. Amoco’ research has shown that isophthalc polyesters offer similar perfor- ‘mance to other premium resin systems at a lower cost. Figure 2 shows the historc difference in cost between isopolyester and vinyl ester resins. Isopolyester resins have been less than hal! the cost of vinyl ester resins for the last 9 years. Dur ing 1989, the median cost per sqft to install an ‘sopolyester system was approximately $4.50 ($4849 m), The median cost per sqft to installa vinyl ester was approximately $5.50 ($59/sq ‘Based on our company's test results, isoph- thalic acid-based resins, when properly formulated, “offer excellent chemical resistance at a moderate cost. Isophthalic polyesters have also shown good adhesion to metal and excellent handling and lass-wetting characteristics. Because ofthese cost/performance advantages, isophthalic polyester resins are currently being used by Amoco in hydro- ‘carbon service The epoxy materials, because of their low shrinkage and superior adhesion are ‘being used for spot patching and sealing jobs. Itis important to remember, however, that any specific resin should be thoroughly tested for alequate cot- rosion resistance prior to field use Selection of Reinforcement Material ‘The reinforcement materials should be easy to handle and compatible with the resin selected. In addition, they should have the required physical properties. The 3 types of reinforcement materials used are glass fabric, glass mat, and glass roving. Glass fabric generally isnot a desirable material for reinforcement because it lacks the strength and thickness to prevent pinholes in the lining. In ad dition, multiple layers of glas fabric are costly, both for material and for installation. Glass mat and glass roving are suitable for use asa reinforcement material in FRP tank bot- tom lining systems. Both materials provide suffi cient strength to meet the stresses involved during the flexing and bending ofa tank bottom. An ad- vantage of glass roving over glass mat is that glass roving produces a higher percentage of glass inthe laminate and, therefore, a lower thermal expansion coefficient than the steel bottom. However, the ad- vantages of glass mat over glass roving are that it is more flexible, less susceptible to high stress, and easier to saturate with resin, Therefore, glass mat is our preferred reinforcement material Installation Methods FRP tank lining systems can be installed by either the spray-up method or the hand lay-up method. Abrasive blasting and priming are necessary with either method to ensure a rough and uncontami- nated surface for good adhesion. Spray-up equip ment includes a gass-chopper gun that mixes the resin components and glass roving atthe time of application. Very rapid rats of deposition are pos- sible with these dual head glss-chopper guns. Tank bottoms having an average resin thickness of Vin, (mm) are usually specified when the spray-up method is used ‘The hand lay-up method isthe preferred method of aplication. Although it is slower, re ‘quires more labor, and has a longer resin gel time than the spray-up method, the hand lay-up method produces a more uniform, consistent ayer. In ad tion, it requires less sill o apply, First, a heavy layer of resin is applied by spay, roller, or brush Second, a glass mat is laid int the wet resin and 2 Journal of Proctive Coatings & LiningsFRP Linings Table 1 Selected Case Histories ning at current Tank No Insallation Inspection —_Servie Comments ‘Sabin, 7 05 wr 1999 Crate Ot No maintenance a ar 1989 Crue Oi hasbeen required a 1971 1989 Cra Of ‘on thes ans Dramrigh, OF = 1965 1989 crate oi ood onion. at 1964 1989 rate Oi Tankpatched once. on 1960 1869 rode Of No prolem with RP. Whiting 3607 1915 78 Jet Fuel ‘These tanks are in 30 im 1s ey Residuals good condition. Sugar Crock, MS Tit 1984 —— etree These tanks are in m5 1985 = HeFuelIPL excelent condition, ‘thoroughly saturated with resin. Then, a seal coat ‘of resin is applied ater the resin-saturated material has gelled. Standardized Approach ‘An FRP tank lining system will have optimum per formance in service if the lining system i properiy applied, The following isa condensed version of Amoco’ standardized approach to applying an FRP tank lining system using the preferred hand lay-up method. Surface Preparation The internal steel surface is cleaned and fred of all organic contaminants and then abrasive blasted in accordance with SSPC-SP 10. The profile is speci- fied to be 1.5 to 3.0 mils (38 to 75 microns). Prime Coat ‘The blasted steel surface is primed with 1 to 3 mils (25 to 75 microns) dry film thickness of a polyamide-cured epoxy primer to “hold” the blast and to protect the steel surface from contamina. tion. The prime coat is applied the same day as blasting and before rusting occurs. Aputty-type material is used to fil in the bottom angle and other sharp angles. The material should be the same as the resin used in laying the bottom, with the adition of fillers and fibers. In cases where the stee! bottom is deeply pitted, a putty is used to fill the pits to create a smooth, surface Resin and Reinforcement Abeavy layer of resin is applied by spray roller, or brush, Then a glass mat is laid into the wet resin and thoroughly saturated with resin, ‘The total dry film thickness ofthe system is determined by the extent of corrosion on the steel bottom and its source. A total dry film thickness of 60 to 80 mils (1500 to 2000 microns) is recom. ‘mended to protect the bottom from internal corro- sion. total dry film thickness of 80 to 120 mils (2000 to 3000 microns) is recommended to protect. the bottom from external corrosion, Finish Coat Asa final coat, a resin-rich layer is applied to the surface of polyester resin laminates a a seal coat to prevent “wicking” of product by capillary action along partially exposed glass fibers. As an aid in ‘curing, paraffin wax is added tothe base resin to form this seal coat. Inspection ‘An inspection is conducted to ensure that the PRP lining has been propery installed. Dry film thickness is determined using a magnetic dry film tester. Before application ofthe seal coat, the thick- ness of the fberglass-reinforced internal tank bot- tom should be tested with a high voltage holiday detector set at the appropriate voltage fora given March 1990/43FRP Linings Louis Sumbry {sa Recorch Scents the ‘gineering Research nd Seizes Dion at wee Corporation. “He proces chic sport {fo Amoco operations world inthe aeas of protective cotngs and ‘omemtale materi ‘Bofrejing Amoco, ‘he ia sia postion with ui Oi atthe Gulf Oi Research Contr in Ptah, PL He recited aS. Chemisty from Florida 4 ners in 162. Hewamember of AST, NACE, NTA and SPC, He sersd on SSPCS Executive Comite Fret 1985 1987 end on ‘PCs Bord of Governors “1987 bert MT ined Amoco Cherical (Camperg in 1987 ater cen 9 BS. Chemical Engineering fram he rivers of Mis Curent, he works in the (Chemica erodes Applicaton Dion at imac Research Contr eas made several presentations at NACE ad SPH eonfreces on the se of ‘pha old based unsaturated palestrsin ‘marine and corasion “ppliatins equine Kass ined he str Intermediates ison of Amoco Chemical Compr i uly 1988 as Marking Soca ‘She alsa Chemistry ‘on the Giver oF ote Dame ‘The authors canbe contacted a moo Ressarch Center, PO. Box 30, Nope, 65658 Ary film thickness. (See NACE Standard Recom= ‘mended Practice RP 0188, Discontinuity (Holiday) ‘Testing of Protective Coatings, for the recommend: ed voltage.) Barcol hardness readings are taken to deter ‘mine proper cure of the resin, Readings are ob- tained using an "Impressor” instrument (Barber Company's Model 934-1). A proper cure is obtained \when the resin manufacturers recommended hardness is reached Field Experiences with FRP Tank Lining System Since the 1960s, Amoco Corporation and its sub. sidiaries have evaluated the effectiveness of using FP linings to combat corrosion in above-ground steel storage tanks. ‘1978 study investigated the physical con- dition of the FRP lining in storage tanks located in Indiana, Missouri, Oklahoma, and Texas. The re- sults indicated thatthe performance of FRP lining was largely favorable, The few failures that did ‘occur were attributed to poor cure, poor adhesion, physical damage asa result of falling tank debri and misapplication. ‘The most recent case histony update was un- ertaken in August 1989 atthe same locations as the 1978 study, together with a few new locations in Texas. For most of the tanks, information was readily available regarding the installation date; last visual inspection date; current service; and maintenance, if any, that has been required over the years. The results for the 1989 update confirmed the previous study’s findings on the versatility of ‘sophthalic unsaturated polyesters. Of the FRP- lined tanks surveyed, approximately 15 percent failed. The failures inthe FRP-lined tanks were not due to the lining itselt, but rather to damaged seals ‘and problems with the roofs, Te tanks with par- ticularly noteworthy case histories are listed in Table 1 ‘The tanks in Drumright have been in service for at least 20 years without any damage tothe FRP lining. The 3 tanks in Sabine showed no indi cation of failure since the FRP lining was installed. Likewise, the tanks in Whiting and in Sugar Creek hhave been in service fr at least 14 and 5 years re~ spectively, without any required maintenance. ‘The length of service of the storage tanks in ‘these 4 locations supports the successful applica- tion of FRP to line the tanks and confirms the ability of isophthalic, acid-based polyesters to resist corrosion, Conclusions Under ideal conditions, the bottom of an above- ground steel storage tank should lst for the de- signed life of the tank, 20 to 30 years. However, corrosive waters or other corrodents accumulate in the tank bottom and reduce the life of the stel plates. Also, the tank bottom steel plates can be at= tacked from external sources such as corrodents present in the soils ‘The use of FRP linings has been shown to be cost-effective method to combat corrosion in above-ground storage tanks. Through design and ‘implementation ofa standardized approach to tank fabrication and repair, the service life of tank bot- toms has been extended, with minimal downtime. ‘When properly applied, gass-reinforced isophthal ie polyester resin has proven to provide excellent corrosion resistance fora lower cost than other ‘premium’ resin systems. Our standardized approach to protecting tank bottoms has mitigated corrosion and has ex tended the service life of the tank bottoms to the designed life ofthe tank itself. This is accom- plished by proper selection and specification ofthe linings, including surface preparation, resin and reinforcement materials, application technique, and inspection procedures. Q References 1. J.B Delahunt, Costing a ining ppliationso Control Storage Tank Comesion, JP, Feb 1987p 2 2. "Problem Soin Rerum,” PCL July 198, p. 12-17, 97. 1A SLE Wyant, KJ Ber. JF Maer, ‘The Use of Reinforced Piste in Petroleum Tk Botfoms" 18h Arua Meeting ofthe Renfro Pastis Division ofthe SPL 4, TE Nayar J Die, ‘he Use of lass Reinforce Pls tis in Petroleum Tank toms, National Assocation of Corrosion Engines, Northeast Region Conference, Oto ber 96h 5. H.R. Bévards, RJ Dit, “Update on Corosion Rss tancz of Renoreed Pasi Linings forthe Repair of Petroleum Tank Batons” SP1 Wes Technical Conference, November 1978 6, MH. Natove ef, “rcing Uae,” PlstiesTechology, Nols 27.5, 1981-988, 44 I Journal of Protective Coatings & Linings