© ARTIS 2016 Manchester Polymer Group, 16th May 2016 1
Composition and Property Changes of
HNBR & FKM Elastomers after Sour Gas
Ageing
C. Norris, M. Bennett, M. Hale & J. Lynch
Overviewo Demanding Environment Facility
o Ageing Protocol
o Lifetime Predictions
o DMA Assessment
o Extract Analysis
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 2
o Extract Analysis
o TGA
o Elemental Analysis
o Degradation Mechanisms
o Conclusions
o Further Work
Sour Gas Testing Capability OverviewEquipment: Six autoclaves (initially) capable of sour gas
exposure testing following:
• NORSOK M-710 (ed. 3 Sep 2014)
• ISO 23936-2:2011
• NACE TM0187-2011
Temperature Range: Ambient to +250°C.
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 3
Temperature Range: Ambient to +250°C.
Pressure Range: Atmospheric to +110bar.
Gas Mixtures:
• 2% H2S/ 3% CO2/ 95% CH4
• 10% H2S/ 5% CO2/ 85% CH4
• 5% CO2/ 95% CH4
• Others upon request
Oil Price
Oil Price
@ sign-off
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 4
Oil Price @
commissioning
Ageing Protocol
Samples: HNBR and FKM compounds (exact formulation unknown).
Relevant Test Standard: NORSOK M710 ed.3/ ISO 23936-2:2011.
Vessel Contents: Water (10%), aromatic solvent blend (60%) and gas(30%) phases. Samples typically maintained in the solvent phase.
30% Gas Phase
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 5
Pressure and Temperature: Vessel pressurised to 60bar at ambient, sealed,and then taken to test temperature.
Lifetime Predictions: Testing of samples at periodic time intervals, at aminimum of three temperatures, allows for lifetime predictions using theArrhenius approach (as specified in NORSOK M-710 & ISO 23936). All testtemperatures above those of the operating environment. 10% Distilled Water
60% Solvent Phase
Lifetime Prediction - Example
Example: Cured FKM polymer aged using aggressive
conditions.
50% change in M50% used as the failure criterion.
M50% modulus plotted as a function of time.
y = -0.0092x + 2.6551
R² = 0.9359
y = -0.0234x + 2.6204
R² = 0.9659y = -0.034x + 2.633
R² = 0.9729
0
0.5
1
1.5
2
2.5
3
M5
0%
(M
Pa
)
166°C181°C195°C
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 6
Extrapolation often used to estimate time to failure,
especially at lower temperatures.
Arrhenius then used to predict lifetime at lower
temperatures.
In this case = 16 years @ 100°C
0
0 5 10 15 20 25 30 35 40 45
Time (days)
y = -9461.3x + 16.676
R² = 0.954
-5
-4.8
-4.6
-4.4
-4.2
-4
-3.8
-3.6
0.00212 0.00214 0.00216 0.00218 0.0022 0.00222 0.00224 0.00226 0.00228 0.0023
ln (
1/t
50)
1/TK
Additional Post-Exposure Testing
Should we rely on basic physical testing to direct lifetime predictions and product
development?
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 7
What additional information can we gain from these testing regimes?
The following analytical study was conducted on samples aged under the most
severe conditions.
DMA: Temperature Dependency• Samples tested in tension, 10Hz, 0.1% DSA & -80°C to +80°C.
• HNBR: Reduced tan δ peak height and higher stiffness indicative of higher crosslink density.
• FKM: Reduced stiffness and Tg suggesting molecular weight reductions had occurred; likely
associated with the loss of side-groups .
Opposing effects for the two polymer types
1.010.0
HNBR Control1.010.0
FKM Control
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 8
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
-80 -60 -40 -20 0 20 40 60 80
Tan
de
lta
Log
(E
'/ P
a)
Temperature (°C)
HNBR Control
HNBR Aged
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
-80 -60 -40 -20 0 20 40 60 80
Tan
de
lta
Log
(E
'/ P
a)
Temperature (°C)
FKM Control
FKM Aged
DMA: Strain Dependency
• Samples tested in tension, 10Hz, +80°C & 0.06 to 6% DSA.
• HNBR: Significant increase in filler-filler interacJons, as indicated by ∆E’ (↑ 79%).
• FKM: Reduced filler-filler interactions observed, possibly due to filler surface modification due to
contact with HF (∆E’ ↓ 7%) .
Opposing effects for the two polymer types
45.00
HNBR Control
30.00
FKM Control
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 9
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
0.01 0.10 1.00 10.00
E'
(MP
a)
DSA (%)
HNBR Control
HNBR Aged
0.00
5.00
10.00
15.00
20.00
25.00
0.01 0.10 1.00 10.00
E'
(MP
a)
DSA (%)
FKM Control
FKM Aged
Extract Analysis GCMS and IR Spectroscopy: • FKM: Unsurprising, the FKM was found to contain very little in the way of soluble matter. No evidence of low
molecular weight polymer was detected but such species may have remained in the ageing vessel fluids.
• HNBR: Naugard 445 antioxidant (↓90%) and a trimellitate plasticiser were found to be deficient in the aged
material, confirming migration of soluble matter to have occurred. The extract was noted as being gummy in nature
– IR spectroscopy revealed the presence of acrylonitrile groups (-C≡N), almost certainly arising from low molecular
weight polymer.100.00
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 10
E59505_A.sp - 30/09/2014 - UNAGED HNBR EXTRACT, SP_ATR
E59505_B.sp - 30/09/2014 - AGED HNBR EXTRACT, SP_ATR
L59410_A.002 - 17/04/2014 - TOTM/TNTM BLEND, SP_ATR
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600.0
52.92
55.0
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
cm-1
%T
TGA: HNBR
-20
-15
-10
-5
0
20
30
40
50
60
70
80
90
100
dW
/dt
We
igh
t /(
%)
HNBR Control
HNBR Aged
1
10
100
Cu
mu
lati
ve
we
igh
t lo
ss (
%)
HNBR Control
HNBR Aged
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 11
• No significant impact on bulk composition (other than reduced extract content).
• The cumulative weight loss profile reveals some modification of the polymer decomposition
behaviour, with more rapid weight loss being recorded for the aged sample over much of the
temperature range – further confirmation of formation of lower molecular weight species.
-30
-25
0
10
20
0 10 20 30 40 50 60 70 80
Time (mins)
0.1
200 300 400 500 600
Cu
mu
lati
ve
we
igh
t lo
ss (
%)
Temperature (°C)
TGA: FKM
-50
-40
-30
-20
-10
0
20
30
40
50
60
70
80
90
100
dW
/dt
We
igh
t (%
)
FKM Control
FKM Aged
1
10
100
Cu
mu
lati
ve
we
igh
t lo
ss (
%)
FKM Control
FKM Aged
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 12
• No significant impact on bulk composition.
• Increase in carbonaceous residue formed during polymer volatilisation.
• Increased carbon black oxidation rate, typically associated with the attachment or formation of pro-
oxidative species.
• More rapid polymer decomposition indicating some level of chain scission.
-600
10
0 10 20 30 40 50 60 70 80
Time (mins)
0.1
100 200 300 400 500 600
Temperature (°C)
SEM EDX Analysis
FKMHNBR
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 13
Presence of localised surface degradation on both compounds.
↑O & S at surface. Low-level oxidative
ageing.
↑O & F at surface. Possible bloom of low
molecular weight fragments. Low-level
oxidative ageing.
Sulphur content of secJoned samples show both to have ↑ sulphur content
Elemental Microanalyses
Quantitative elemental microanalyses of extracted samples
(aged – unaged values in wt%)
C -1.36 -3.5
H 0.1 -0.29
N -0.12 Not tested
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 14
S 0.55 0.73
F Not tested -0.67
• Sulphur content increased for both HNBR and FKM = permanently bound.
• HNBR – Reduction in N content further confirmation of loss of low MW polymer.
• FKM – Reduction in H & F content confirms dehydrofluorination. Significant reduction in carbon
content suggests loss of polymeric fragments.
Mechanisms Summary: HNBRData suggests that additional C-Sx-C is the dominant mechanism with regard to increased
stiffness. No evidence of H reduction to support additional C-C linkages.
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 15
*arbitrary numbers
Mechanisms Summary: FKMData suggests molecular weight reductions and dehydrofluorination to be the dominant
mechanisms:
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 16
*arbitrary numbers
Conclusionso The test fluids outlined in NORSOK M710 ed.3/ ISO 23936-2:2011 were found to impart
muliple modes of degradation to both HNBR and FKM compounds after relatively short
exposure times.
o Stiffening of HNBR attributed to additional crosslinking, plasticiser extraction and
increased filler-filler interactions.
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 17
o Softening of FKM attributed to dehydrofluorination and loss of polymer fragments.
o Crosslinking, chain scission, dehydrofluorination, oxidative ageing, filler surface
modification and extraction all likely to be occurring at different rates.
o Understanding of the mechanisms involved can be used to develop more robust
formulations for sour service conditions.
Further Work
• Currently running a Box-Behnken experimental
design to further understand the effects of
temperature, H2S concentration and time on the
different modes of degradation.
• HNBR material compounded at ARTIS –
therefore, composition fully understood.
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 18
• Can we use parameters other than standard
physical properties to estimate lifetimes?
• Can we correlate the ageing mechanisms occurring
during service with those of the accelerated
ageing?
Thank You!
Interested?
© ARTIS 2016 Manchester Polymer Group, 16th May 2016 19
Interested?
Please contact us:
Tel: 01225 896500
www.artis.uk.com
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