Best Practices of FRP and Elastomeric Linings for Steel ... · Best Practices of FRP and...
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Best Practices of FRP and Elastomeric Linings for
Steel and Concrete Tanks
Abstract:
Since case studies have demonstrated that achieving a service life of 15-20 years in
harsh environments is the norm, a number of projects continue to utilize FRP and
elastomeric liners. However, in order to have an adequate service life, many factors
including, material choice, training and inspection are required. This paper will
examine the use of polymeric linings, the common lining problems, the NACE/SSPC
standards and the industry practices necessary to produce a lining that will fulfill its
expected service life.
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Author Biography:
Michael P. Yee
The Managing Partner of RT Consults who also controls an engineering and 3rd-party inspection company for the FRP and coatings industry. Has over 10 years of experience in the nonmetallic industry and is a NACE Level III Certified Coating Inspector with a background in chemical engineering and construction management. He is actively involved in the nonmetallic technical committees at NACE and also ICRI. Presenter for a number of professional organizations over the years who continues to strive for excellence in providing technical services and support for many leading petrochemical companies in chlorine and sulfuric acid, in addition to the offshore oil industry.
Richard Taraborelli, P.E.
The owner of RT Consultants with over 35 years of experience in the protective coatings and nonmetallic industry. He is a registered professional engineer in the state of Texas. Performed over 2,000 failure analysis and other projects in his career and continues to provide technical services and support to many leading petrochemical Fortune 500 companies.
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Table of Contents
Introduction.................................................................................................................... 4
Material Selection.......................................................................................................... 4
Resins............................................................................................................................ 4
Fiber-Reinforced Polymers (FRPs)................................................................................. 5
Flake Glass Liners......................................................................................................... 7
Rubber Linings............................................................................................................ 10
Application and Quality Issues.................................................................................... 13
Quality Inspection Program…..................................................................................... 15
Conclusion………………..…..................................................................................... 16
References………………..…..................................................................................... 17
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Introduction
Chemical facilities face a number of issues when dealing with corrosion and harsh
chemicals. The conventional method of addressing these issues is to adequately-
prepare the steel surface and then apply the proper coating to protect it from the
elements. However, in chemical facilities, harsh chemicals are essential to the
process and require adequate containment and reliable service in order to keep
the facilities operational. This paper will address the issues that these facilities face
when dealing with severe chemical exposure and protection; namely, with respect
to the nonmetallic linings and construction materials where high-priced alloys and
thin coatings are not strong enough to withstand the constant thermocycling and
harsh facility operations.
Material Selection
Material selection determination is made based on existing tanks and secondary
containment areas that are primarily made out of steel and concrete. The
chemicals that require special attention include, but are not limited to, sulfuric acid,
chlorine, phosphoric acid, hydrochloric acid, sodium hydroxide, sodium
hypochlorite (bleach), potassium hydroxide, brine, white and black liquor,
hydrocarbon solvents and alcohols. The containment of these chemicals requires
materials that are considered unique, but continue to be rigorously used around
the world, like fiberglass-reinforced polymers (FRP), rubber linings and resin-rich
flake glass liners.
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Resins
While there are many resins on the market, the primary resin used in linings is the
thermosetting resin. Thermosetting resins cure to produce an infusible solid
material that does not melt when heated. The most commonly-used thermoset
resin system is epoxy vinyl ester with a chemically-resistant glass as the corrosion-
protection layer for caustic service. For stronger acids, the novalac epoxy vinyl
ester is commonly-used due to its chemical resistance. These combinations can
also be used as the liners for steel tanks, though a solid FRP-construction will
traditionally see a longer service life and lower installed cost due to the labor
reductions associated with automation in fabrication shops. Additionally, there is
limit to the vessel size and logistics costs when the vessels grow past the 30’-
diameter mark.
Fiber-Reinforced Polymers (FRPs)
FRPs are used daily in hostile environments. While the majority of FRP
applications and uses are located in Asia, it is equally-matched to the demand in
the United States, Canada and Europe. The use of chemically-resistant resins with
glass has been around since its introduction in the 1950’s by Dow Chemical, as
well as several other Japanese companies that have been incorporating
composites. FRP was created for its use in hostile, chemical environments and
thus, different product lines were created to address different services for each
environment. Today, a lot of these resins are being added to coatings to provide a
similar level of chemical protection to steel and concrete surfaces. Technology has
not changed much since the 1970’s and there are numerous case studies that
show that a properly-designed FRP vessel and lining with excellent quality,
properly maintained, inspected, and operated can reliably last for over 20 years.
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Figure 1: FRP Lined Steel tank with a BPO/DMA Cure
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Figure 2: Hand-lay up method of application
Flake Glass Linings
Flake glass linings are relatively-new to the coatings industry and are seeing a lot
of adoption by the petrochemical industry. They were developed in the 1960’s but
never really started to take off until the 1980’s when they then branched into many
different industries and companies. As in FRP, these resin-rich, flake glass linings
use a significant quantity of resin in the formulation. They also use the same
catalyst, benzo-peroxide, to fully-cure the system. Trowel methods are normally
employed to both provide a high material-to-surface transfer and to minimize air
bubble issues. These linings include glass flakes in the material and are reinforced
with fiberglass that is woven for concrete linings and unreinforced for steel linings.
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Figure 3: Sulfuric Acid Containment
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Figure 4: Reinforced Mat Lining Application
Figure 5: Trowel Method of Flakeglass Lining
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Figure 6: Holiday Testing
Rubber Linings
Rubber lining has been around since the 1890’s when the autoclave method of
curing was invented. Not much has changed, as evidenced by the steel linings of
rail car tanks for mild chemical and brine storage. Rubber can be either natural or
synthetic, but is a very robust material that handles impact and abrasion very well.
The upfront cost is less than FRP and is an economical choice for mild chemical
and brine service. On average, when properly installed, it will last longer than thin
paint coatings and unreinforced linings. It is applied by first preparing the surface
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and then applying a primer/adhesive that normally comes in sheets. Different
systems may use natural rubber as a bonding interface with the synthetic rubber
forming a composite. There are a number of things to observe when inspecting
the surface as well as when repairing a rubber lining and it is important to note the
difficulty of doing so in the field.
Figure 7: Rubber Sheets cut and fitted together inside a tank roof
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Figure 8: Issue with Stitching Quality
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Application and Quality Issues:
Lining systems are labor intensive and will typically involve 66-85% of a project’s
labor cost in the United States. This is the result of the surface preparation,
application and quality, which encompass a successful project. Surface
preparation is considered the foundation of the lining system. Steel and concrete
require the most rigorous surface preparation because there is little allowable
variation since almost all will call for a NACE 1/SSPC-SP5 white metal blast.
Before the abrasive blast, a detergent pressure wash must be performed in order
to remove salts, sulfites and nitrate contaminants from the surface. Concrete is a
difficult material to achieve a proper surface profile since it is heterogeneous and
very sensitive to moisture. When mechanically removing the surface, the laitance
must be removed in order to reveal any small and large aggregates. The required
and best-consensus standards available are either IRCI 300R8.1 or NACE
6/SSPC-13. Once surface preparation is complete, the application process soon
follows in an effort to either protect the steel from flash rusting or to take advantage
of the coating window. The substrate surface must be 5-degrees Fahrenheit higher
than the dew point in order to prevent moisture from interfering with the cure and
adhesion of the lining system. The application process must be initiated at
temperatures in excess of 50-degrees Fahrenheit because it is almost impossible
to obtain a complete resin cure without the application of external heat. Corners
and edges must be reinforced through the use of putties or flashings. The tank
must also have the radius filled-in with putty or reinforcement from the bottom to
the shell in order to prevent the formation of air pockets. This holds true for weld
seams and other metal deformities as well. A comprehensive guide to this practice
is found in the standard NACE SP01788. The surface preparation process is
considered a critical quality control point. It must have a proper surface profile and
be free of contaminates prior to application.
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Figure 9. Steel Pits Found on a Relining Project
Resin lining applications require an accurate gel time in order to provide sufficient
working time to remove air bubbles from the laminate. A resilient wetting primer is
recommended in order to provide an interface that will assist with expansion and
thermal cycling performance. The primer must be applied with a thickness of no
more than 4 mils in order to prevent detrimental effects on the adhesion. Following
manufacturer product data sheets during the application process is important and
training is needed for optimal lining performance. Quality inspections must be
performed and evaluated in order to ensure proper application techniques are
being used. Rubber application is normally done in sheets and requires the proper
technique with respect to the seam-stitching. Curing with either autoclave or
atmospheric steam must be performed within the time span specified by the
manufacturer. Hardness should be inspected and verified in order to conform to
manufacturer cure specifications prior to initiating chemical service.
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Quality Control Program
There are three motivating factors in completing a successful project: safety,
productivity, and quality. Safety in chemical plants is non-negotiable and therefore
the balance of productivity and quality is always at odds with one another. The
reality that exists today is that there is a failure rate of at least one out of three in
premature failures within 4-5 years. The expected life in proper service of these
lining systems with excellent quality, properly maintained, inspected, and operated
can reliably last for over 20 years. The main quality issues come from the
inadequate surface preparation requirements for the lining system and also issues
with application. In addition, testing and specifying the right system and material
choice is just as crucial since low concentrations of impurities in the chemical
stream will also result in premature failure. A lot of these lessons are imparted from
experience and not recognized by material suppliers since it would be detrimental
to the product line. An example of this happening is the issue of the recoating
window for a lining system. A manufacturer stated on product data sheets that it
could be recoated within 30 days. However, the coating cure was very sensitive to
moisture and so it was revised after a technical meeting to be 3 days. After
numerous adhesion failures, it was then finally revised to just one day which
resulted in the project being terminated and reworked. Another example is the
wrong curing mechanism and the lack of environmental conditions during
application. Moisture was seen in the laminate and also the hypochlorite contained
in the tank would have attacked the promoter used (Cobalt) for the FRP lining
system resulting in failure. There are many examples but the lesson is always the
same in the need of doing the project right the first time. There isn’t much that can
be done after failure has taken place, it normally results in total rework.
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Conclusion
With respect to each material, all waste and product streams must be accounted
for in order to determine proper material selection. Chemical services have special
requirements that demand respect for the chemicals being used as well as for the
dangerous/lethal concentrations being created. As a result of the changing service
conditions, one should not rely solely on the material service tables. Solution
mixtures in a waste stream can wreak havoc on any system that was designed for
only one concentration. Lower concentrations of certain chemicals as well as
alkaline solutions can be detrimental to the material being used. Permeation and
temperature changes can drastically-affect any laminate performance; therefore,
quality assurance and technical specifications addressing these issues is of vital
importance. There are many plants that had to close their doors due to chemical
remediation fines and regulatory requirements after leaks and spills resulted from
containment failures.
There is an important need for nonmetallic engineering and for the quality
inspections used to determine satisfactory results in a material’s performance.
While the best materials and methods can be used, the system won’t provide
reliable service if the quality is lacking. This is why 3rd-party inspections are
required, in order to ensure that details and issues are timely-addressed and
corrected.
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References 1. ACI Committee 440, “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures (ACI 440.2R-08),” American Concrete Institute, Farmington Hills, MI, 2008, 80 pp. 2. ASME RTP-1-20013, “Reinforced Thermoset Plastic Corrosion-Resistant Equipment,” American Society of Mechanical Engineers, New York, NY, 2013. 3. SSPC-SP 13/NACE NO. 6, “Surface Preparation of Concrete (2003),” SSPC: The
Society of Protective Coatings, Pittsburgh, PA.
4. ACI Concrete Repair Terminology,
http://www.concrete.org/Technical/CCT/FlashHelp/ACI_Terminology.htm, ACI
International, Farmington Hills, MI.
5. ICRI CSP 4-5, ICRI Committee 310, “Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair (ICRI 310.2R-2013),” International Concrete Repair Institute, St. Paul, MN, 48 pp. 6. ASTM C582, “Standard Specification for Contact-Molded Reinforced Thermosetting Plastic (RTP) Laminates for Corrosion-Resistant Equipment,” ASTM International, West Conshohocken, PA, 2009, 7 pp. 7. ASTM D7234, “Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers,” ASTM International, West Conshohocken, PA, 2012, 9 pp.
8. ASTM D4541, “Standard Test Method for Pull-Off Strength of Coatings Using
Portable Adhesion Testers,” ASTM International, West Conshohocken, PA, 2009.
9. ASTM D2583, “Standard Test Method for Indentation Hardness of Rigid Plastics by
Means of a Barcol Impressor,” ASTM International, West Conshohocken, PA, 2001.