Hydrocarbon Processing - February 2021 - 66

Maintenance and Reliability
TABLE 6. Cure study evaluations conducted at different temperatures
Cure temp = 24°C (75°F)

Cure temp = 38°C (100°F)

Time, hr

Shore D
hardness

Reduction of
FTIR peak, %

Time, hr

Shore D
hardness

Time, hr

Reduction of
FTIR peak, %

7.4

168

56
80

Hardness over time

FTIR peak reduction over time

70
Area under epoxy peak

60
D-hardness

Reduction of
FTIR peak, %

T = 75°F
T = 100°F
T = 130°F

40
30

50
40
30
T = 75°F
T = 100°F
T = 130°F

Cure temp = 55°C (130°F)

0
0

Time, hr

120

144

168

FIG. 8. Graph of FTIR peak reduction over time.

FIG. 7. Graph of hardness change over time.

a fully cross-linked system (i.e., a fully cured system), the ultimate Tg must be reached, which is achieved by curing the epoxy
at the measured Tg of 134°C (273°F). Note that successful usage
may not require full cross-linking, but only a specific percentage. While this study is not fully vetted in this article, it should
be considered for the practical application capacity of a system.
This phenomenon can be seen in FIG. 6, where each line represents the FTIR spectroscopy of a different cure temperature.
The top line represents a specimen cured at 100°C (212°F) for
19 hr, where there is no epoxy peak at 912cm-1 because the resin
is fully cured. The red line has a small peak at 912cm-1, which
corresponds to a specimen partially cured at 55°C (130°F) for
9 hr. Finally, the blue line was cured at 24°C (75°F) for only
2 hr; the depth of the epoxy peak means that there is not yet
a crosslinking reaction between the epoxy and amine, indicating that the sample is not fully cured. The area under the epoxy
peak curve is what is considered for calculation purposes-the
smaller it is, the more cured the sample is until it disappears,
indicating a fully cured resin.
If this is not possible in the field of use conditions that this
ECRS will be subjected to, then a minimum cure must be known.
Since it was determined that chemical compatibility was success66 FEBRUARY 2021 | HydrocarbonProcessing.com

ful at the previous time and temperature values, these were used
as the baseline to plot expected cure curves for the system. TABLE 6
displays the correlation of time with Shore D hardness values and
percent reduction in FTIR peak values at three of the primarily
reviewed temperatures. FIGS. 7 and 8 show the change in hardness and the FTIR peak, respectively, over time. As can be seen
within the figures, the previous statement regarding hardness being only one piece of the puzzle for cure measurement is shown
to be true. Specifically, the samples cured at 24°C (75°F) reached
their full hardness in 2 d or less, while the associated FTIR peak
measurements took up to 7 d to reach the minimum levels to be
considered to have a resistance to the 98% sulfuric acid.
Based on this information, it can be determined that specific
curing protocols should be used for this system when it is going
to be used with 98% sulfuric acid to ensure adequate resistance.
The graphs can provide some ideas and indications of how to
monitor and ensure that this cure level has been met when utilized in the field for repairs.
Qualifying the final ECRS. Upon completing the validation
testing, and successfully characterizing the requirements and
meeting the primary goals set forth, the last phase is to complete
the full qualification testing to the ASME PCC-2 Article 4.1 and

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Hydrocarbon Processing - February 2021

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