Composition and Property Changes of HNBR & FKM Elastomers after Sour Gas Ageing C. Norris, M. Bennett, M. Hale & J. Lynch

Transcription

1 Composition and Property Changes of HNBR & FKM Elastomers after Sour Gas Ageing C. Norris, M. Bennett, M. Hale & J. Lynch ARTIS 2016 Manchester Polymer Group, 16 th May

2 Overview o Demanding Environment Facility o Ageing Protocol o Lifetime Predictions o DMA Assessment o Extract Analysis o TGA o Elemental Analysis o Degradation Mechanisms o Conclusions o Further Work ARTIS 2016 Manchester Polymer Group, 16 th May

3 Sour Gas Testing Capability Overview Equipment: Six autoclaves (initially) capable of sour gas exposure testing following: NORSOKM-710 (ed.3sep2014) ISO :2011 NACE TM Temperature Range: Ambient to +250 C. Pressure Range: Atmospheric to +110bar. Gas Mixtures: 2%H 2 S/3%CO 2 /95%CH 4 10%H 2 S/5%CO 2 /85%CH 4 5%CO 2 /95%CH 4 Others upon request ARTIS 2016 Manchester Polymer Group, 16 th May

4 Oil Price Oil sign-off Oil commissioning ARTIS 2016 Manchester Polymer Group, 16 th May

5 Ageing Protocol Samples: HNBR and FKM compounds (exact formulation unknown). Relevant Test Standard: NORSOK M710 ed.3/ ISO : % Gas Phase Vessel Contents: Water (10%), aromatic solvent blend (60%) and gas (30%) phases. Samples typically maintained in the solvent phase. 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 a minimum of three temperatures, allows for lifetime predictions using the Arrhenius approach (as specified in NORSOK M-710 & ISO 23936). All test temperatures above those of the operating environment. 60% Solvent Phase 10% Distilled Water ARTIS 2016 Manchester Polymer Group, 16 th May

6 Lifetime Prediction - Example Example: Cured FKM polymer aged using aggressive conditions y = x R² = C 181 C 195 C 50% change in M50% used as the failure criterion. M50% (MPa) y = x R² = y = x R² = M50% modulus plotted as a function of time. 0.5 Extrapolation often used to estimate time to failure, especially at lower temperatures Time (days) y = x R² = Arrhenius then used to predict lifetime at lower temperatures. Inthiscase=16years@100 C ln (1/t 50 ) ARTIS 2016 Manchester Polymer Group, 16 th May /T K

7 Additional Post-Exposure Testing Should we rely on basic physical testing to direct lifetime predictions and product development? What additional information can we gain from these testing regimes? The following analytical study was conducted on samples aged under the most severe conditions. ARTIS 2016 Manchester Polymer Group, 16 th May

8 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 T g suggesting molecular weight reductions had occurred; likely associated with the loss of side-groups. Opposing effects for the two polymer types HNBR Control HNBR Aged FKM Control FKM Aged Log (E'/ Pa) Tan delta Log (E'/ Pa) Tan delta Temperature ( C) Temperature ( C) ARTIS 2016 Manchester Polymer Group, 16 th May

9 DMA: Strain Dependency Samples tested in tension, 10Hz, +80 C& 0.06 to 6% DSA. HNBR:Significant increase in filler-filler interac ons, 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 HNBR Control HNBR Aged FKM Control FKM Aged E' (MPa) E' (MPa) DSA (%) ARTIS 2016 Manchester Polymer Group, 16 th May DSA (%)

10 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 %T cm-1 E59505_A.sp - 30/09/ UNAGED HNBR EXTRACT, SP_ATR E59505_B.sp - 30/09/ AGED HNBR EXTRACT, SP_ATR L59410_A /04/ TOTM/TNTM BLEND, SP_ATR ARTIS 2016 Manchester Polymer Group, 16 th May

11 TGA: HNBR HNBR Control Weight /(%) HNBR Control HNBR Aged dw/dt Cumulative weight loss (%) 10 1 HNBR Aged Time (mins) Temperature ( C) 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. ARTIS 2016 Manchester Polymer Group, 16 th May

12 TGA: FKM FKM Control FKM Aged Weight (%) FKM Control FKM Aged dw/dt Cumulative weight loss (%) Time (mins) No significant impact on bulk composition Temperature ( C) Increase in carbonaceous residue formed during polymer volatilisation. Increased carbon black oxidation rate, typically associated with the attachment or formation of prooxidative species. More rapid polymer decomposition indicating some level of chain scission. ARTIS 2016 Manchester Polymer Group, 16 th May

13 SEM EDX Analysis HNBR FKM Presence of localised surface degradation on both compounds. O & S at surface. Low-level oxidative ageing. O & F at surface. Possible bloom of low molecularweight fragments. Low-level oxidative ageing. Sulphur content of sec oned samples show both to have sulphur content ARTIS 2016 Manchester Polymer Group, 16 th May

14 Elemental Microanalyses Quantitative elemental microanalyses of extracted samples (aged unaged values in wt%) C H N Not tested S F Not tested 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. ARTIS 2016 Manchester Polymer Group, 16 th May

15 Mechanisms Summary: HNBR Data suggests that additional C-S x -C is the dominant mechanism with regard to increased stiffness. No evidence of H reduction to support additional C-C linkages. *arbitrary numbers ARTIS 2016 Manchester Polymer Group, 16 th May

16 Mechanisms Summary: FKM Data suggests molecular weight reductions and dehydrofluorination to be the dominant mechanisms: *arbitrary numbers ARTIS 2016 Manchester Polymer Group, 16 th May

17 Conclusions o The test fluids outlined in NORSOK M710 ed.3/ ISO :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. 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. ARTIS 2016 Manchester Polymer Group, 16 th May

18 Further Work Currently running a Box-Behnkenexperimental design to further understand the effects of temperature, H 2 S concentration and time on the different modes of degradation. HNBR material compounded at ARTIS therefore, composition fully understood. 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? ARTIS 2016 Manchester Polymer Group, 16 th May

19 Thank You! Interested? Please contact us: Tel: ARTIS 2016 Manchester Polymer Group, 16 th May