Fiberglass Reinforced Thermoset
Plastic
Tank & Piping Standards
Fiberglass Tank & Pipe Institute
Sullivan (Sully) D. Curran PE, Executive Director
Executive Summary
The purpose of this paper is to provide the design engineer and
those responsible for purchasing tanks and piping for use in
aggressive environments with an understanding of the design,
material system, fabricating methods and quality control standards
for the manufacture of fiberglass products. While purchasing
decisions are based on quality, service and price, this paper
provides guidance on how to improve the quality and safety of
fiberglass Reinforced Thermosetting Plastic (RTP) tanks and piping
(i.e., pipe, fittings, and adhesives).
There are many manufacturers of commonplace plastic and fiberglass
products, but only a limited number of tank and piping manufacturers
are equipped to meet recognized fabrication standards
for design and construction. This list is further reduced to those manufacturers
who have established Quality Control and Quality Assurance programs for their
manufacturing facility, fabrication process and end product. Certain of these
manufacturers voluntarily submit to third party conducted Quality Assurance
programs.
Two nationally recognized organizations have developed the most widely used
programs for fiberglass FRP tank and piping manufacturers. American Society of
Mechanical Engineers (ASME) and Underwriters Laboratories Inc. (UL) have
developed standards and conduct Quality Assurance programs for aboveground RTP
tanks and underground FRP tanks and piping, respectively. ASME and UL Certified
tanks and piping are each labeled with a uniquely numbered “RTP-1” or “UL” stamp
to signify their respective certifications. While not all fiberglass products
produced by these ASME and UL qualified manufacturers (e.g., hoods, ducts,
stacks, large diameter pipes) are ASME or UL labeled, the purchaser of these
other products benefits from the overall qualifications necessary to meet the
third party Quality Assurance program that is in place.
The design engineer and those responsible for the purchasing of tanks and piping
for application in an aggressive environment will likely place product quality
high on their list of priorities. The specifying of ASME and/or UL third party
qualified manufacturers should achieve this goal. Further, by specifying this
level of standard, the user is more likely to receive competitive quotations for
like products. Finally, the Quality Assurance programs in place relieves the
buyer of the costs associated with conducting plant inspections to ensure that
the products meet their purchasing specification.
Introduction
Fiberglass reinforced thermosetting plastic (“fiberglass”) first became a viable
alternative to protected steel, stainless steel and exotic materials in 1950.
That year centrifugal cast fiberglass piping was first used in the crude oil
production industry as a solution to corrosion problems. During the mid-50’s
developments in manufacturing with polyester and epoxy resins resulted in the
application of fiberglass tanks and piping in the chemical industry. By the
mid-60’s fiberglass was accepted for the storage and handling of underground
flammable and combustible liquids and industrial, municipal water, sewage and
pulp and paper processing applications.
It was during the 1960’s that manufacturers began to develop nationally
recognized standards and test methods for fiberglass storage and fiberglass piping systems.
Today, there are a number of nationally recognized standards and specifications
for fiberglass tanks and fiberglass piping. While there are standards developed for
military applications, e.g., MIL standards for helicopter rotor blades,
following is a list of civilian organizations with published standards and
specifications:
|
Fiberglass |
Civilian Organizations
|
|
Tanks & Piping |
API American
Petroleum Institute
ASME American Society of Mechanical Engineers
ASTM American Society for Testing and Materials
AWWA American Water Works Association
FM Factory Mutual Research
NSF National Sanitation Foundation
UL Underwriters Laboratories Inc. |
Background ~ General
Fiberglass tanks and fiberglass piping contain glass fiber reinforcement embedded in cured
thermosetting resin, hence the term Reinforced Thermosetting Plastic (RTP)
describes the fiberglass material system. This composite structure typically
contains additives such as pigments and dyes. By selecting the proper
combination of resin, glass fibers, additives and design, the fabricator can
create a product that meets the equipment designer’s performance standard.
Following is a discussion on the components of a fiberglass material system.
Background ~ Glass Fibers
Glass Fiber Types: All glass fibers begin as individual filaments of
glass drawn from a furnace of molten glass. Many filaments of glass are formed
simultaneously and gathered into a “strand” and a surface treatment “sizing” is
added to maintain fiber properties. Glass fibers are designed for several
applications, some of which are shown as follows:
|
Types |
Applications |
E or E-CR
E
C |
Acid Environment
Alkali Resistance
Chemical Resistance |
Glass Fiber Forms: Glass fibers are
manufactured for use by the tank and piping fabricator in the following forms:
- Continuous Roving: Supplied as strands of
glass fiber on a cylindrical spool. Typically used in filament winding and
chop-gun spraying applications.
- Reinforcing Mats: Supplied as chopped
strands held together with a resinous binder. Typically used for hand lay-up
applications.
- Surface Veils: Supplied as light weight
reinforcing mats to provide a resin rich smooth surface which increases
corrosion resistance without the crazing that would occur in non-reinforced
resin.
Glass Fiber Reinforcement: The mechanical strength of a fiberglass product
depends upon the amount, type and arrangement of glass fiber reinforcement
within the material system. Strength increases proportionally with the
amount of glass fiber reinforcement. Following are three general types of
fiber orientation:
- Uni-directional: Glass fiber strength is greatest to forces applied in the
direction of the fibers. Continuous strand filament winding incorporates
this principle.
- Bi-directional: Some of the fibers are positioned at an angle to the rest
of the fibers. An example is to change the direction of the filament winding
at alternating levels within the tank or pipe laminate.
- Multi-directional: The fibers are positioned in near equal directions.
Such arrangements are obtained with the use of chop-gun applications of
continuous roving and reinforcing mats.
Background ~ Resins
The second major component of fiberglass tanks and piping is the
thermosetting resin system. Thermoplastic resin is one of two basic groups
of resin systems, but is not used with glass fiber reinforcing. A comparison
of the two resin systems is shown below:
- Thermoplastics are resins that are normally solid at room temperature, but
are softened by heat and will flow under pressure. Typical applications
include household kitchenware, children’s toys, bottles and other common
items.
- Thermosetting plastics are resins that undergo an irreversible reaction
when cured in the presence of a catalyst. They cannot be re-melted and are
insoluble.
Fiberglass products use only thermosetting resin systems of which there are
two generic types, epoxy and polyester resins. The resin system is chosen
for its chemical, mechanical and thermal properties. Epoxy resins are used
primarily for the manufacture of small diameter piping, whereas polyester
resins are commonly used for large diameter piping and storage tanks.
Polyester resins come in many variations with different properties to resist
acids, caustics and high temperatures.
Additional compounds are added to resins such as pigments, monomers (e.g.,
styrene, vinyl toluene) catalysts (e.g., organic peroxides), hardeners and
accelerators. For example, catalysts are typically added to polyester resins
to accelerate the curing action, whereas epoxy resins do not use catalysts.
Resistance to Aggressive Environments
Resistance to corrosion in aggressive environments is one of the primary
reasons for specifying fiberglass tanks or piping. Typical types of
corrosion do not affect fiberglass. This would include galvanic, aerobic,
pitting and inter-granular corrosion which harms metals but not fiberglass.
Although fiberglass resists a wide range of chemicals and temperatures, it
requires the right design, fabrication and installation to match the
appropriate application. For example, fiberglass may be subject to chemical
attack from hydrolysis, oxidation, pyrolysis or incompatible solutions. The
proper resin/glass matrix will minimize chemical attack.
Industry Standards and Specifications
Industry Segments Certain industry trade organizations have developed
fiberglass tank and/or piping standards and specifications that are specific
to their industry. In addition, certain third party organizations have
developed standards and specifications that are applicable to several
industries with similar corrosive environments. Following is a discussion of
civilian fiberglass standards and specifications and their applications:
Trade Association Standards & Specifications:
Potable Water Pipelines
The American Water Works Association (AWWA) maintains the following
standards for small and large diameter pressure piping for potable water
pipelines and tanks.
Pipe C950-88 Fiberglass Pressure Pipe
Tanks D120-84 Thermosetting Fiberglass-Reinforced Plastic Tanks
Petroleum Production & Exploration
The American Petroleum Institute (API) maintains the following standards for
high and low pressure crude oil and gases, and produced water (e.g., saline
solutions) line piping, well drilling tubulars and oil field non-potable
water tanks:
| Pipe |
Spec. 15HR
Spec. 14LR
R.P. 15TL4
|
Specification for High Pressure Fiberglass Line Pipe
Specification for Low Pressure Fiberglass Line Pipe
Recommended Practice for Care and Use of Fiberglass Tubulars |
| Tanks |
Spec. 12P |
Specification for Fiberglass Reinforced Plastic Tanks |
Third Party Standards & Specifications:
Flammable and Combustible Liquids Storage and Handling Applications
Underwriters Laboratories Inc. (UL) is a nationally recognized third party
testing laboratory that maintains performance standards. *UL testing and
approval also involves the labeling of the product and a listing service.
The listing service includes the periodic inspection of the manufacturing
facilities as part of a quality assurance program. UL testing standards for
fiberglass piping and tanks are shown below:
| Pipe |
*UL 971 |
Nonmetallic Underground Piping for Flammable Liquids |
| Tanks |
*UL 1316 |
Glass-Fiber-Reinforced Plastic Underground Storage Tanks for
Petroleum Products |
Chemical, Industrial and Pulp & Paper Applications
The American Society for Testing and Materials (ASTM) maintains standard
specifications for the testing of fiberglass materials and the fabrication
of fiberglass tanks and piping. The most commonly used standards are listed
below:
| Pipe |
D 2997-90
D 2996-88 |
Centrifugally Cast “Fiberglass” (Glass-Fiber-Reinforced
Thermosetting-Resin) Pipe
Filament-Wound “Fiberglass” (Glass-Fiber-Reinforced
Thermosetting-Resin) Pipe
|
| Tanks |
D 4097-88
D 3299-88
D 4021-92 |
Contact-Molded Glass-Fiber-Reinforced Thermoset Resin
Chemical-Resistant Tanks
Filament-Wound Glass-Fiber-Reinforced Thermoset Resin
Chemical-Resistant Tanks
Glass-Fiber-Reinforced Polyester Underground Petroleum Storage
Tanks |
The American Society of Mechanical Engineers (ASME) maintains standards for
certain applications of fiberglass piping and storage tanks as shown below.
In the case of the tank standard, ASME conducts a manufacturing facility and
*tank certification program. This program includes the application of an
ASME stamp on the tank and periodic quality assurance inspections by ASME
inspectors.
| Pipe |
B31.3 |
Chemical Plant and Petroleum Refining Piping |
| Tanks |
*RPT-1 |
Reinforced Thermoset Plastic Corrosion Resistant Equipment |
Quality Control & Quality Assurance
Quality Control: The manufacture of fiberglass tanks and piping requires the
control of materials and processing parameters to ensure consistency and
reliability of the end product. Manufacturers maintain control by
implementing a quality control program which includes raw materials
inspection, vendor certification, in-process inspection, finished product
inspection and testing.
Quality Assurance: There is a second level of quality control known as a
quality assurance program. This program may be conducted by a qualified
outside party and should include the outside party evaluation of the quality
control program in place to ensure that it will perform as intended.
Finally, the outside party should conduct periodic unannounced plant
inspections to verify the performance of the quality control program.
Certification Programs
General Typically a certification program includes the assignment of a
unique identification number to each product manufactured. The manufacturer
records all manufacturing, inspection and testing data for each unique
number and maintains a filing system for possible future retrieval. There
are two methods of certification, self and third certification.
Self Certification Self certification is when the manufacturer certifies
that the product meets a certain standard or specifications cited in the
purchase order. The validity of the certification is based on the quality of
the manufacturing process when the product was produced.
Third Party Certification Third party certification is when a qualified
third party participates in the certification process and shares in the
control of the unique numbers assigned to each product. Two examples of such
programs for fiberglass tanks and piping are the UL “Labeling” and the ASTM
“Stamp” quality assurance programs. UL labels are laminated onto each
fiberglass tank, pipe and fitting for underground flammable and combustible
liquid service. ASME RTP stamps are laminated onto aboveground tanks for
chemical or other industrial service applications.
The manufacturer pays for the third party certification service by first
paying a fee to have the production facility and product approved or
certified. Then there is an ongoing fee for the periodic plant inspections
and the purchasing of UL labels or ASME stamps to certify that each product
meets the standard setting organization’s standard. As a result, there is an
added cost to the manufacturer for the third party quality assurance program
and product certification. However, the added product cost represents an
overall savings to the end user. In terms of user costs, there are savings
by minimizing design engineering, purchasing specifications, plant
inspections and the longer trouble free life of a quality product.
Third Party Certification of Aboveground Storage Tanks
The ASME RTP-1 Reinforced Thermoset Plastic Corrosion Resistant Equipment
standard applies to Reinforced Thermoset Plastic (RTP) vessels in corrosive
and otherwise hazardous material service operating at pressures not to
exceed 15 psig external and /or 15 psig internal above any hydrostatic head.
The RTP-1 standard addresses the following requirements a fabricator must
meet to be certified and manufacture tanks with a RTP-1 stamp.
Shop Qualifications
Each fabricating facility is surveyed by a team of ASME Inspectors who will
conduct an inspection of the following capabilities:
- Fabricator’s Facility and Equipment The qualification survey includes the
general shop area and certain specific are i. e., raw material storage
areas, resin mixing and dispensing, molds (e.g., tank heads) and laboratory
equipment.
- Personnel The fabricator’s organization shall include specific personnel
designated for each of the following functions:
• Design and Drafting
• Quality Control
• Material Control
• Fabrication
• Laminators (i.e., a person who makes laminates)
• Secondary Bonders (i.e., a person who joins & overlays subassemblies)
- Quality Control Program and Record System The fabricator shall establish
and maintain a Quality Control Program for all phases of the fabricating
process. This program includes a procedure that assures current designs and
specifications are in place. A record keeping system shall be in place to
provide a paper trail for all fabricating phases.
- Materials Inspection Requirements The fabricator is required to conduct
minimum inspections and testing of reinforcing material i.e., glass-fiber
and resins and curing agents when received. These minimum procedures are
cited in the standard.
- Qualifications of Laminators and Secondary Bonders The Inspector will
qualify laminators and secondary bonders based on their ability to produce
demonstration laminates to meet all provisions of the standard. They shall
be re-qualified every three years.
- Demonstration of Capability The fabricator is required to produce
demonstration laminates for each type of laminate the shop will use on
vessels fabricated to the standard. This would include the production and
testing of a filament wound vessel and hand lay-up and/or spray-up laminates
using all glass-fiber mats and/or glass-fiber roving in the chopper-gun
process. The latter two laminates are required for the fabrication of heads
or when joining the subassemblies of vessels together.
- Demonstration Vessel To complete this requirement the fabricator must
have a comprehensive understanding of the standard. It involves the
fabricator’s ability to design, execute drawings, qualify demonstration
laminates, establish design values, qualify Laminators and Secondary Bonders
and follow an effective Quality Control Program. After vessel testing it
shall be sectioned to reveal the details and integrity of laminates and
secondary bonds.
- Materials Specifications The fabricator must use resins and glass-fiber
reinforcements that meet the standard and were used in the qualification
laminates.
- Test and Analytical Methods The standard includes accepted test and
analytical methods for physical mechanical properties. These include stress
analysis methods and examination by using acoustic emissions in conjunction
with a hydrostatic test.
Accreditation
An accredited fabricator is one who holds a current ASME RTP-1 “Certificate
of Authorization.” The certificate is issued for a three year period for
each shop location, after which time the shop must be re-certified. After
initial accreditation, ASME will conduct a continuing audit program of the
Quality Control Program i. e., a Quality Assurance program.
Third Party Certification of Underground Storage Tanks & Piping
Underwriters Laboratories Inc. (UL) is an independent testing laboratory
established to investigate materials, products, equipment, constructions and
systems with respect to hazards affecting life and property. UL
certification i.e., “Listing” is the largest nationally recognized testing
laboratory and is often required by local and regional building codes for
the storage and transfer of flammable and combustible liquids.
Underground Storage Tanks
UL 1316 “Glass-Fiber-Reinforced Plastic
Underground Storage Tanks for Petroleum Products” standard applies to
spherical or horizontal cylindrical atmospheric-type Reinforced Thermoset
Plastic (RTP) tanks that are intended for the underground storage of
petroleum-based flammable and combustible liquids, alcohols and
alcohol-blended fuels. The UL 1316 standard addresses the following
requirements a fabricator must meet to be certified and manufacture tanks
with a UL Mark.
Performance Standards
The manufacturer must submit a representative tank to UL’s testing facility
for an engineering evaluation of the following components:
- General Standards Lift lug strength, pipe connections, man-ways and other
fittings are standardized for the installer.
- Significant Performance Requirements Following is a summary of major
performance requirements included in the UL testing protocol:
- Internal Pressure Two internal pressure tests are performed on the
demonstration tank. First, the tank is placed aboveground on a sand bed with
no other support. It is then filled with water to capacity for one hour and
shall show no damage. Second, the tank shall withstand without rupture an
internal pressure 25 psig for 10 foot and 15 psig for 12 foot diameters,
respectively.
- External Pressure The demonstration tank is to be buried in a pit, filled
with water and then subjected to an internal vacuum of 17.9 psig with out
failure.
- Aged Properties Coupons are cut from the demonstration tank and are aged
at 158 degrees F in an oven for up to 180 days and must retain 80% of the
original flexural and impact strength.
- Impact and Cold Exposure Coupons are conditioned for 16 hours at 20
degree F and must retain 80% of their original flexural and impact strength.
- Material Compatibility Coupons are cut from the demonstration tank and
immersed in 100 degree F test liquids for up to 180 days and must retain 50%
of their flexural and 30% of their impact properties. The immersion liquids
include gasolines, heating fuels and gasoline blends up to 100% ethanol and
methanol.
Underground Piping UL 971 “Underground Piping for Flammable Liquids”
standard applies to primary and secondary containment non-metallic pipe and
fittings (piping) intended for use underground to transfer petroleum-based
flammable and combustible liquids, alcohols, and alcohol-blended fuels. The
UL 971 standard addresses the following requirements a fabricator must meet
to be certified and manufacture piping with a UL Mark.
Performance Standards
The manufacturer must submit a representative samples to UL’s testing
facility for an evaluation of the pipe, fittings and adhesives.
- Internal Pressure Primary Piping Test samples are subjected to 1.5
million cycles at a rate of 23 cycles per minute. Following this test, the
samples are subjected for five minutes to a hydrostatic pressure of two
times the rated pressure and then for one minute at five times the rated
pressure.
- Bending Bending moment and bending load tests are conducted on pipe
fittings threaded or bonded to the pipe and then tested for leaks.
- Aged Properties Samples are tested essentially the same as for fiberglass
tanks.
- Impact and Cold Exposure Piping is tested before and after 16 hours of
conditioning at minus 29 degrees F by dropping from a six foot height onto
pavement and by dropping a steel ball on the piping. The piping then must
then pass a leakage test.
- Material Compatibility Immersion tests and test fluids are essentially
the same as for fiberglass tank coupons.
- Permeability Eighteen inch lengths of pipe are filled with the test
fluids and sealed with end caps using the test adhesive or screwed fitting.
The primary pipe and containment pipe are weighed over a 180 and 30 day
period respectively, to determine if the test fluids permeate the materials.
Accreditation
An accredited (i.e., Listed) fabricator with Underwriters Laboratories has
submitted a demonstration product to UL engineers who have conducted an
investigation of the product for compliance with the UL 1316 or UL 971
standard. The registered UL Mark on a product is a means by which a
manufacturer can show that UL approves the product as having met the
standard test protocol and that the manufacturer participates in a third
party quality assurance program. This program typically includes quarterly
unannounced UL representative plant inspections of the manufacturer’s
quality control program.
Summary
- Since the 1950’s Fiberglass Reinforced Thermosetting Plastic (RTP) has
developed as a proven material for tanks and piping applications in an
aggressive environment.
- The fabricator has many different glass-fiber, resin and additive RTP
matrices from which to design the appropriate material system for the
intended application.
- Fiberglass standards and specifications are generally industry and/or
application specific. An exception may be found with certain ASTM standards.
- Product quality is an important factor when making a purchasing decision
for the storage and transfer of aggressive materials.
- Product quality assurance is attainable by:
• Buyer’s tight specifications and plant inspections
• Industry standards and self certification by the fabricator, or
• Third Party Standards and Quality Assurance Program
- American Society of Mechanical Engineers (ASME) and Underwriters
Laboratories Inc. (UL) are the two nationally recognized organizations that
have developed standards and conduct Quality Assurance programs for the
manufacture of aboveground RTP tanks and underground tanks and piping,
respectively.
- Third party Quality Assurance Programs:
• Provide an objective standard
• Require management dedication to the quality process
• Result in a higher level of overall service and product quality for all
fiberglass products produced at a qualified facility.
- In the absence of third party quality programs the next best option is to
know your fabricator.
Fiberglass tank stds Rev2
May 1, 1997
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