RILSAN® Polyamide 11 in Oil & Gas Off - HCL Fasteners Ltd

3.3 Chemical aging
In offshore applications, certain offshore
fluids and chemicals can have a detrimental
effect on polyamide 11 performance. For
each application, the specific chemicals
should be reviewed in order to estimate
service life.
Polyamides, and in particular polyamide
11, are very resistant to many types of
chemicals. Polyamide 11 is very resistant
to oils and hydrocarbons as well as to a
large variety of solvents. In contrast to
standard polyamides 6 and 66; polyamide
11 shows only little absorption of water
and is also resistant to diluted acids and
bases. Due to its increased flexibility and
molecular structure, it is also highly resistant
to stress cracking, unlike most other thermoplastics.
Polyamide 11 can be used in conjunction
with a great variety of standard offshore
chemicals. A detailed description of compatibilities
is given in sections 3.8 and 3.9.
Because chemical species attack thermoplastic
resins when they are absorbed,
diffusion and solubility play important roles
in the assessment of chemical compatibility.
There are two effects induced by absorbed
species – an influence on the mechanical
properties due to plasticization, and a
chemical effect leading to loss of material
performance.
Specific examples of absorption and
plasticizer extraction are given in sections
3.6 and 3.7 on methanol-and glycol-based
hydraulic liquids.
The main chemical effect is reduction in
polymer molecular weight due to hydrolysis.
Hydrolysis is the reverse reaction of the
chain-forming polycondensation reaction.
It can be induced by water at elevated
temperatures and is accelerated by acids
and, to some extent, also by bases. Due to
the importance of hydrolysis in aging related
to offshore applications, section 3.5
describes the phenomenon in detail.
ELONGATION AT BREAK (%)
Fig. 6A Evolution of Yellowness Index (YI) in Xenotest aging
40
35
30
25
YI 20
15
10
5
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0
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500 1000 1500 2000 2500
TIME (HOURS)
EQUILIBRIUM SWELLING AND CHEMICAL COMPATIBILITY
OF COMMON SOLVENTS AND OFF SHORE FLUIDS
Solvent Swelling at 20°C in % weight Compatibility
Benzene 7.5 good up to 70°C / swelling
Toluene 7 good up to 90°C / swelling
Cyclohexane 1 good
Petrol ether 1.5 good
Decaline < 1 good
Gasoline depends on type, mostly < 2% good
Kerosene depends on type, mostly < 2% good
Ethylene glycol 2.5 good up to 60°C / swelling
Glycerol 1 good up to 60°C
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