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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.