metals and coating performance increase
dramatically with increasing depth:
1. Temperature
2. Formation fluid pressure
3. Gas contaminants (H2S, CO2)
4. Microbiological contaminants.
To understand how an internal pipe
coating system degrades over time at
high operating temperatures, several
factors must be considered, such as the
environment to which it will be exposed during its lifetime. However, the
most critical property for the success of
Fusion Bonded Epoxy (FBE) coating systems is its glass transition temperature,
Tg. The Tg is the temperature at which
a change of the polymer (coating) from
a hard and relatively brittle solid state
to a viscous or rubbery condition occurs.
At or above this temperature, the permeation rate of oxygen, moisture, and other
ionic substances increases considerably,
which may lead to rupture of the polymer structure and ultimately failure of
the coating system.
Temperatures above 110 °C (230 °F)
start to represent a conflict in selection of
protective coating systems for corrosion
control because many of the most popular internal pipe FBE coating systems
available today have a Tg of around 109
°C (228 °F). Table 1 shows a comparison of an FBE coating currently available
on the market and advertised as able to
withstand 205 °C (400 °F), to our newly
developed product.
Development of a New
Internal Pipe Coating
System
When Axalta staff began research and
development work on a new FBE inter-
nal pipe coating system for the oil and
gas market, researchers examined many
specifications from end-users in order
to find the most difficult required auto-
clave qualification testing to pass. The
JO Wafra “Test Condition 4” was agreed
upon as the most difficult testing environ-
ment. The autoclave test conditions are:
• Temperature: 400±2 °F (205±1 °C)
• Duration: 96 Hours
• Pressure: 755± 10 psi
• Gas Phase: 20% (20% H2S, 15%
CO2, and 65% CH4)
• Hydrocarbon Phase: 40% (Toluene/
Kerosene 1:1 by Volume)
•Water Phase: 40% (25% NaCl
Solution).
After exposure, the barrier properties of the coating were evaluated using
Electrochemical Impedance Spectroscopy
and compared with a sample of the coating not exposed to the autoclave environment. The results of the evaluation were
Figure 1. Pre- and post-autoclave exposures for coating “C”.
Figure 2. Pre- and post-autoclave exposures for the experimental Axalta coating system.
