Hydrocarbon Processing - February 2021 - 62

Maintenance and Reliability
compatible composite repair system. These include:
* Mechanical, metallic clamp/patch/enclosure: Reasons
for using a compatible composite repair system include:
° Cost-This option can be costly, depending on the
full scope of repair.
° Limitation on size-This option can have limitations
based on the size of pipe requiring repair, including
its overall weight.
° Lead times-This option can be associated with
long lead times, depending on the scope of repair.
* Cut and replace: A reason for using a compatible
composite repair system includes:
° Downtime-Time spent out of operation for this
option can be extremely costly to the facility
due to loss of production.
* Existing composite repair systems: Reasons for using
a compatible composite repair system include:
° Compatibility-Most existing, commercially
available composite repair systems are not compatible
(or not proven to be compatible) with sulfuric acid
at concentrations above 40% or temperatures
above 24°C (75°F).
° Testing-Most existing, commercially available
composite repair systems do not have the physical
testing in place to validate claims of compatibility
in operating conditions.
Development plan. Commercially available epoxy systems

were reviewed for potential inclusion in the testing program;
however, despite claims of compatibility, there were other hurdles that prevented them from being considered. The correct
selection and combination of the epoxy resin and the hardener
components determine the final characteristics and suitability
of the system for a given environment, and, as such, a set of criteria was developed for review of formulations.
TABLE 1. Gel time test results

Sample no.

Gel time (min)

150

137.4

153

154

Average

A newly required epoxy resin formulation was to be designed for use as both a primer and saturant on repairs, and to
meet recommended operational conditions. Additionally, the
chosen fibers had to be able to withstand the conditions. When
a corrosive chemical comes into direct contact with a fiber, if
the wrong type and grade of fiber are selected, then the chemical can degrade the fiber and destroy the resin bond, resulting in a significant reduction in structural properties. Due to
known reaction levels between sulfuric acid and carbon fibers,
a glass fiber was chosen for the new system reinforcement.
Among the primary goals that a development project for the
repair system should include are:
1. Glass transition temperature of 130°C (266°F) or above
2. Gel time longer than 1 hr
3. Lap shear strength greater than 580 psi (4 MPa)
4. Easy to mix epoxy parts A and B
5. Chemical resistance to sulfuric acid up to
98% concentration.
A stringent formulation and testing process was conducted
to achieve the targeted properties through various epoxy formulations. Various concentrations of base resins and advanced
hardeners were mixed and tested until the desired sulfuric acid
resistance, glass transition temperature (Tg ), viscosity and gel
times were achieved. Once the primary goal properties were
obtained, it was necessary to evaluate and adjust percentages of
raw materials to meet all the specific performance goals. Various fabric types, architectures and combinations were tested for
sulfuric acid resistance to find the final fiber-reinforced plastic
(FRP) makeup most compatible for sulfuric acid environments
with concentrations up to 98%. Results of the final formulation
testing, along with some developmental discoveries of the system's curing protocols, are provided in the following section.
Upon completion of the initial research and evaluation of a
suitable composite combination, full qualification testing to the
ASME PCC-2 Article 4.1 standard (and, similarly, to the ISO
24817 standard) was completed to fully qualify and characterize the new system and its design properties and capabilities.
Material evaluation. Firstly, a thorough research was con-

ducted to determine the appropriate epoxy formulation to be
used that would theoretically perform to the primary goals and
1.5

148.6

1.0

Sample no.

Lap shear strength (psi)

1,150

1,140

950

1,132

1,023

1,307

1,266

1,295

Average

1,158

62 FEBRUARY 2021 | HydrocarbonProcessing.com

Heat flow, W/g

TABLE 2. Lap shear test results
0.5

0.0

-0.5

120 °C

134 °C(T)

142 °C

-1.0
0

100

FIG. 2. Tg of epoxy, using DSC.

150
Temperature, °C

200

250

300

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Hydrocarbon Processing - February 2021

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