FRP LININGS IN ABOVEGROUND STORAGE TANKS
B. R. Bogner*
Senior Engineer
Amoco Chemical Company, Amoco Research Center
Naperville, Illinois, U.S.A.
and
L. C. Sumbry
Slaff Reseurch Engineer
Amoco Corporalion, Amoco Research Center
I50 W. Warrenville Road, B-1, Naperville, Illinois 60566, U.S.A.
ABSTRACT
This paper describes installation methods and long term performance testing of
fiberglass reinforced plastic tank linings. 1t shows lining large aboveground fuel
tanks with isopolyestcr fiberglass reidorced plastic linings can be done quickly
and these linings are cost effective. The paper also shows a proven method for
installing the tank linings.
-
*Address for comspondcnce:
Amoco Research Ccntcr
150 W. Wanunville Road, E-2B
Napenrille. nlinois 60566. U.S.A.
Fax: 708-361 -7979
April 1995
The Arabian Journal for Science and Engineering, Volume 20, Number 2.
361
FRP LININGS IN ABOVEGROUND STORAGE TANKS
INTRODUCTION
Fiberglass-reinforced plastic (FRP) linings are a cost effective solution to internal corrosion of aboveground
steel storage tank bottoms. Standards and specifications, howevcr, are valuable to ensure proper material selection
and installation techniques. Unsaturated isopolycstcr rcsins, offering excellent corrosion resistance at a moderate
price, are often selected to be among the most cost effective resins. OLhcr material selection includes specifying the
type and level of reinforcements. The proper installation melhod is also specified to standardize surface
preparation, installation, and inspection.
Problems with Internal Tank Bottoms
Although steel tanks are designed to last 20 to 30 years, if the tank bottoms are not properly protected from
corrosion, they may have to be replaced aftcr only 5 years. Typically, thin film (15 to 30 mils [380 to 750 microns]
dry film thickness) coatings such as m i n e epoxy, coal tar epoxy, or epoxy phenolic are used internally on new
steel tank bottoms to protect against internal corrosion. Thin film coatings, however, are not suitable for use over
heavily pitted and thinned internal tank bottoms [I, 21. In Lhese situations, FRP linings are required to provide
protection against corrosion from the stored product and structural reinforcement for steel bottoms exposed to
corrosion by Lhe external environrncnt.
Table 1 compares relative costs against expected life cycles for a variety of methods of tank bottom repair.
History of the Use of Coatings for Lining Internal Tank Bottoms
In the 1960s. epoxies and polyesters replaced sand-filled bitumen coatings to repair, reinforce, and thus extend
the life of steel bottoms exposed primarily to external corrosion. Today, FRP lining systems have proven an
acceptable, cost-effective alternative to rcplacing corroded steel bottoms, whelher the source of corrosion is
internal (i.e., from the product contained within thc tank) or cx~crnal(i.e., from exposure to the soil).
---
THE EFFECT OF MATERIAL SELECTION ON PERFORkIANCE
Testing of Resin Systems
Research test methods (ASTM C686, ASTM C581) [3]have been used to demonsuate the level of corrosion
resistance needed to ensure long-term laminate durability to minimize thc risk of leakage. A series of tests
Method
Table 1. Comparative Costs of Aboveground Tank Repair.
Expected Life
Cost
Commcnts
(Jfcan>
(Slsq mcter)
Replacement of stccl bottom
with another steel bottom
190-235
Tank out of service thrce weeks.
Epoxy paint coating plus
caulking (300-375 microns)
Can only be used on tanks with no
structural damage.
Isopolycster with one layer
chopped s m d mat (45-65
Talk out of service about one weck.
mils)
Glass flake coaling isopolyesrcr
resin (500-750 microns)
10-20
The Arabian Journal for Science and Engineering. Volume 20. Number 2. .
43-75
Tank our of service about one week.
Tank must be structurally sound.
April 1995
u
B. R. Bogner and L. C. Sumbry
-
examined five different resin types to evaluate the corrosion resistance of bisphcnol-A epoxy, bisphenol-A
polyester, isophthalic polyester, orthophthalic polyester, and vinyl ester FRP panels.
Standard laminates were consuuctcd using each of these resin systems. One side of these panels were then
exposed to a variety of chemical media, including benzene, distilled water. 5 percent acetic acid, 5 percent nitric
acid, 5 percent sodium hydroxide, and 5 percent sulfuric acid. The panels were evaluated after 3 months, 6 months,
and 12 months for laminate adhesion (ASTM D 3359), hardness (ASTM D 2583). and visual appearance.
Likewise, the range of panels were immersed in the chemical media to provide two-sided exposure for a period
up to a year. At intervals of 1 month, 3 monlhs, 6 monlhs, and 1 year of exposure, the flexural properties and
hardness of the panels were measured. A plot of the data on a log-log scale was extrapolated out to 10 years to
predict the long-term pcrformance of each rcsin system. To bc considered acceptable, a material must retain a
minimum of 50 percent of both its flexural properlies and hardness.
Summary of Resin Resistances
Specific test results of the above resins have been previously reported [4-61. The following general
characterizations of the resins are based on the retention of physical properties and visual appearance of the panels.
Resin Selection Criteria
Corrosion resistance is not the sole determining factor for resin selection. A desirable system must cure at room
temperature, exhibit good adhesion to Lhe steel tank floor, have sufficiently low viscosity to allow for easy wet-out
of the glass fibers and removal of entrapped air, and il must be economically reasonable, providing the best
performance for the lowest cost. Amoco's research has shown t h a ~isophthalic polyesters offer similar performance
to other premium rcsin systems at a lower c o s ~[7].
-
Based on our company's test results, properly formulated isophthalic acid-based resins [8] not only offer
excellent chemical resistance at a moderate cost, but have also shown good adhesion to metal and excellent
handling and glass-wetting characteristics. Becausc of these cost/performance advantages, isophthalic polyester
resins are currently being used by Amoco in hydrocarbon service. Because of their low shrinkage and superior
adhcsion, epoxy materials are used for spot patching and sealing jobs.
120
Excellent
100 ;
90'~
8
80-
.-
70-
Best straight line
Good
60-
Acceptable
50
r
Unacceptable
o
-
.-5
40-
c
Q)
30[r
20
1
2
3
4
5
6 7 891012
18
24
36
48
607284
120
Immersion time, months
Figure I .I-low Loss oJ Properries During O n e Yeczr Predicts Long Term Resistance.
April 1995
The Arabian Journal for Science and Engineering, Volume 20, Number 2.
Selection of Reinforcement Material
Reinforcement materials should be easy to handle and compatible with the resin selected. In addition, they
should have the required physical properties. The three types of reinforcement materials used are glass fabric, glass
mat, and glass roving. Glass fabric is generally not desirable material for reinforcement because it lacks the
strength and thickness to prevent pinholes in ihe lining. In addition multiple layers of glass fabric are costly, both
for material and for installation.
Either glass mat or glass roving are suitable for use as a reinforcement material in FRP tank bottom lining
systems. Both materials provide sufficient strength to meet the stresses involved during the flexing and bending of
a tank bottom. An advantage of glass roving over glass mat is that roving results in a higher percentage of glass in
the laminate and, therefore, a lower thcrmal expansion coefficient than the steel bottom. Conversely, glass mat is
more flexible than glass roving and therefore less susceptible to high stress, and it is easier to saturate with resin.
Therefore. glass mat is our prcferrcd reinforcemcnt material.
Installation Methods
FRP tank lining systems can be installed by eirhcr the spray-up me~hodor the hand lay-up method. Abrasive
blasting and priming are necessary with eilher melhod to ensure a rough and uncontaminated surface for good
adhesion. Spray-up equipment includes a glasschopper gun that mixes the resin components and glass roving at
the time of application. Very rapid rates of deposition (2-4 kglmin) are possible with these dual head glass-chopper
guns. Tank bottoms having an average resin thickness of j/, in (6 mm) are usually specified when the spray-up
method is used.
The hand lay-up method is the preferred method of application. Although it is slower, requires more labor, and
has a longer resin gel time than h e spray-up method, the hand lay-up method produces a more uniform, consistent
layer. In addition, it requires less skill to apply. First, a heavy layer of resin is applied by spray, rollcr, or brush.
Second, a glass mat is laid into the wet resin and dloroughly saturated wiih resin. Then, a seal coat of resin is
applied after the resin-saturated material has gelled.
11
t?
k
L.
3000
2500
0
P 1 .oo
d-
i
Vinyl Ester/
I
-
2
8
'P
4
T """ Z
2
+lsoo 2
mnn
IsopoIyester
- /
-
Orthopolyester
Source: Plastics Technology
Year
Figure 2 . Lf~~sarurured
Polyesfer Resin Prices (U.S.)
364
The Arabian Journal for Science and Engineering, Volume 20. Number 2.
April 1995
-
B. R. Bogner and L. C.Surnbry
Installation of Lining
An FRP tank lining system will have optimum performance in service if the lining system is properly applied.
The following is a condensed version of Amoco's approach to applying an FRP tank lining system using the
preferred hand lay-up method.
Surface Preparation
The internal steel surface is cleaned and freed of all organic contaminants and then abrasive blasted in
accordance wilh SSPC-SP 10. Thc surface prol'ilc or "roughness" is specified to be 1.5 to 3.0 mils (38 to 75
I
microns).
Prior to the application of a protective lining, small holcs or thin areas in the corroded tank bottom are patched
with heavy layers of resin reinforced with glass cloth, glass mat, glass roving, or metal sheets. For repair and
reinforcement, the physical properties of isophhalic polyester and bisphenol-A epoxy resins provide the greatest
resistance to chemicals and solvents. Such resins are most easily applied by the hand lay-up method, and most
effective when reinforced with 2 f / , oz per sq ft (700 g/m2) of glass mat or glass roving applied to a total dry film
thickness of 60 to 150 mils (1.8 mm to 4.5 mm) (Figure 3). Note that two 1 f / , oz. per sq. ft. (350 g/m2) mats are
also acceptable.
Prime Coat
The blasted steel surface is primed with 1 LO 3 mils (25 LO 75 microns) dry film thickness of a polyamide-cured
epoxy primer to "hold" the blast and to protect the steel surface from contamination. The prime coat is applied the
same day as blasting and before rusting occurs.
-
A putty-type material is used to fill in the bottom angle and other sharp angles. The material should be the same
as the resin used in laying the bottom, with the addition of fillers and fibers. In cases where the steel bottom is
deeply pitted, a putty is used to fill the pits to create a smooth surface.
lr-
1 5 mils (0.4 mm) isopolyester resin
60-100 mils (1-3 mm) isopolyester laminate
2.5 ozlsq ft (700 g/m2) glass mat
I
grout over row of rivets
1mils (0.05 rnm) primer
2
Figure 3. Cross Sccfion oj'ltrrtritmre.
April 1995
The Arabian Journal for Science and Engineering, Volume 20. Number 2.
365
8. R. Bogner und L. C. Sumbry
Resin and Reinforcement
A heavy layer of resin is applied by spray, rollcr, or brush. Then a glass mat is laid into the wet resin and
thoroughly saturated with resin.
The total dry film thickness of the system is delemined by Ihe extent of corrosion on the steel bottom and its
source. A total dry film dlickness of 60 to 80 mils (1500 to 2000 microns) is recommended to protect the bottom
from internal corrosion. A total dry film thickness of 80 to 120 mils (2000 to 3000 microns) is recommended to
protcct the bottom from external corrosion.
Finish Coat
As a final coat, a resin-rich layer is applied to the surface of polyester resin laminates as a seal coat to prevent
"wicking" of product by c a p i l l q action along partially exposed glass fibers. As an aid in curing, paraffin wax is
added to the base resin to foh'ihis seal coat.
Inspection
An inspection is conducted to ensure that the FRP lining tias bccn properly installed. Dry film thiclcness is
determined using a magnetic dry film tcster.
Before application of the seal coat, h e polyester resin laminates should be tested with a high voltage holiday
detector set at the appropriate voltage for a given dry film thickness. (See NACE Standard Recommended Practice
RP 0188, Discontinuity (Holiday) Testing of Protective Coatings, for the recommended voltage.)
Barcol hardness readings are taken to determine proper cure of the resin. Readings are obtained using an
"Impressor" instrument (Barber Company's Model 934-1). A proper cure is obtained when the resin
u
manufacturer's recommended hardness is rcached.
FIELD EXPERIENCES WITH FRP TANK LINING SYSTEM
Since the 1960s. Amoco Corporation and its subsidiaries have evaluated the effectiveness of using FRP linings
to combat corrosion in above-ground steel storagc tanks.
A 1978 study [6] investigated the physical condition of the FRP lining in storage tanks located in Indiana.
Missouri, Oklahoma, and Texas. The resulls indicated that the performance of FRP lining was largely favorable.
The few failures that did occur were attributed to poor curc, poor adhesion, physical damage as a result of falling
tank dcbris, and misapplication.
Thc most recent case history updatc was undcrrakcn in August 1989 at the same locations as the 1978 study,
togcther with a fcw ncw locations in Tcxas. For most of tllc tanks, information was readily available regarding the
installation datc; last visual inspcclion datc; currcnt scrvicc; and mrrintcnancc, if any, that has been required over
the years.
The rcsults for the 1989 update confirmed tlic prcvious study's lindings on the versatility of isophthalic
unsaturatcd polycstcrs. Of the FRP-lincd tanks survcycd, approximately 15 percent failed. These failures were not
due to Lhc linings, but rather to damaged scals and problcms with lhe roofs. The tanks wilh particularly noteworthy
case histories arc listcd in Table 2.
Thc tanks in Drumright, OK have bccn in scrvicc for a1 least 20 years without any damage to the FRP lining.
The three tanks in Sabine, TX showcd no indication of failure since the FRP lining was installed. Likewise, the
tanks in Whiting, IN and in Sugar Crcck. MO have bccn in service for at least 14 and 5 years, respectively, without
any rcquired maintcnancc.
The lcngth of scrvice of h e storagc tanks in thcsc locations supports the successful application of FRP to line the, ,
tanks and confirms Ihe ability of isophlhalic, acid-bnscd polyesters to resist corrosion.
366
The Arabian Journal for Science and Engineering. Volume 20. Number 2.
April 1995
B. R. Bogner and L.C. Sumbry
'I'able 2. Selected Case Histories.
---/
Tank No.
Linulg
Installation
Last
Insuecrion
Current
Service
Comments
Sabine, TX
405
41 1
412
Drumright. OK
6693
6694
6997
Whiting, IN
3607
3620
Sugar Creek, MO
114
115
L
Crude Oil
Crude Oil
Crude Oil
No maintenance
has been required
on these tanks.
Crude Oil
Crude Oil
Crude Oil
Good condition,
Tank patched once.
No problem with FRP
Jct Fucl
Hcavy Residuals
1084
1985
Jct Fuel JP4
Jct Fuel JP4
These tanks are in
good condition. -
These tanks are in
excellent condition.
CONCLUSIONS
Under ideal conditions, the bottom of an abovcground steel storage tank should last for the designed life of the
tank, 20 to 30 years. Howevcr, waicr or other corrosives can accumulate in Lhe tank bottom and reduce the life of
the steel plates. The tank bottom stecl plates can also I>eattacked from exte~nalsources such as corrosives present
in the soils.
The use of FRP linings has becn shown to be a cost-efkctive method to combat corrosion in above-ground
storage tanks. Through design and implemcntation of a standardized approach to tank fabrication and repair, the
service life of tank bottoms has been extcndcd, will1 minimal downtime. When properly applied, glass-reinforced
isophthalic polyester resin has provcn Lo providc exccllcnt corrosion resistance for a lower cost than other premium
resin systems.
Our standardized approach lo protccting tank bottoms has miligatcd corrosion and has extended the service life
of the tank bottoms to the dcsigncd lire oS t l ~ clank itself. This is accomplished by proper selection and
specification of the lining systcms. including surl'acc preparation, resin and reinforccmcnt materials, application
technique, and inspection proccdurcs.
REFERENCES
[I]
[2]
[3]
[4]
u[5]
J. R. LeBleu. "The Ability of FRP Linings to Rridgc Corrosion Holcs in Tank Bottoms", Paper No. 36, Muterials
Technology Institute's Second Interttational Syrnl)osiuttr on /\bovegrouttd Sforage finks, January 1992.
Corrosion", JPCL, Fcbruary 1987, p. 24.
J. F. Dclahunt, "Coating and Lining Applications to Control Stor;~gc
"Problcm Solving Fomtn", JPCL, July 1988, pp. 12-17,97.
J. F. Wygant, K. J. Bcrg, J. F. Maycr, "Thc Usc of Rcirlforccd Pliis~icsin Petroleum Tank Bottoms", 18th Annual Meefing
of [he Reinforced Plasfics Llivision of the SPI.
J . F. Mayer, R. J. Dictcric. 'Thc Usc oS Class Rcinforccd Plastics in Pctrolcu~nTank Rottorns", Nafional Association of
Corrosion Engineers, Northeast Region Conference, Ocwbcr 1964.
April 1995
The Arabian Journal for Science and Engineering, Volume 20, Number 2.
367
B. R. Bogner and L.C.Sumbry
[6] H.R. Edwards. R. J. Dictcrte, "Update on Corrosion Rcsistancc of Rcix~forccdPlastic Linings for the Repair of Petroleum
Tank Bottoms", SPI West Technical Conference. Novcnlbcr 1978.
[7] M. H. Naitove, ed., "Pricing Update", Plastics Techrwlogy. 27-35 (1981-1989).
[a] "Make Corrosion Resistant Unsaturated Polyesters with PA",
in BufletinIP-866. Chicago: Amoco Chemicals, 1991.
Paper Received 12 April 1994, Accepted 8 January 1995.
b
368
ntr Arabian Journal for Science and Engineering, Vulwne 20. Number 2.
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