© 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

enquiries@artis.uk.com

www.artis.uk.com