THE DAMAGE CAUSED BY RGD AND HOW IT MAY BE REDUCED. Dr Sabine M G Munch, Glyn J Morgan, Dr Barry Thomson

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1 THE DAMAGE CAUSED BY RGD AND HOW IT MAY BE REDUCED Dr Sabine M G Munch, Glyn J Morgan, Dr Barry Thomson RubberCon 2012, Oslo Norway, May 2012

2 Overview Why is rapid gas decompression a problem? How can RGD resistance be promoted? How can the material be qualified as RGD resistant? 2

3 Why is RGD a problem for polymers? RGD = Rapid Gas Decompression Rapid release of gas System at equilibrium under gas pressure The gas dissolved in the polymer escapes The polymer is saturated with gas The polymer expands 3

4 Mechanism of gas decompression in elastomers RGD test performed on a transparent elastomer 2 min after RGD Several days after RGD Bubble formation at nucleation sites Coalescence of bubbles: Fewer but bigger 4

after RGD Several days after RGD Bubble formation at

5 RGD damage in composites and thermoplastics 5

6 RGD damage in elastomers 6

7 The underlying causes of RGD damage Static applications Dynamic applications ageing ageing + RGD RGD damage is influenced by: Operating conditions or environmental factors Intrinsic material properties Manufacturing Sealing arrangement or housing design 7

Operating conditions or environmental factors Intrinsic

8 Fixed parameters Operating conditions or external factors Type of gas Pressure Higher solubility can lead to more RGD damage High pressure means more gas dissolved in the rubber High pressure may also result in rubber compaction Concentration Temperature Partial pressures have to be considered Effect on gas solubility and diffusion in the elastomer Effect on the elastomer mechanical properties Ageing Seal performance after ageing in the operating conditions 8

Concentration Temperature Partial pressures have to be considered Effect on gas solubility and diffusion in the

9 Fixed parameters Operating conditions or external factors Gas depressurisation rate The slower, the better Number of decompression cycles The fewer, the better 9

10 Material properties Stiffness Tear strength Gas diffusion The higher, the better 10

11 Manufacturing Batch-to-batch variability Processing 11

12 Sealing arrangement or housing design Seal thickness Groove fill The smaller, the better Explore different design Very important parameter The higher, the better 12

13 RGD is positively influenced by Low gas pressure Low gas concentration in the polymer Low temperature Low decompression rate Fewer decompression cycles High stiffness High tear strength High diffusion coefficient Clean mixing and processing Low seal cross-section or thickness High groove fill 13

cycles High stiffness High tear strength High diffusion coefficient Clean

14 What do I now do with my virtually perfect rubber? Test it and Qualify it What test shall I perform? In what conditions? Material testing Functional testing 14

15 MATERIAL TESTS Standard available to check RGD performances NACE TM1092 NACE TM0297 TOTAL GS PVV 142 NORSOK M-710 ISO Qualifying is good, but be aware of the test conditions! 15

PVV 142 NORSOK M-710 ISO 23936-2 Qualifying is

16 ISO Stems from NORSOK M-710 Flexible in terms of temperature and pressure Comprehensive damage rating system Well defined acceptance criterion Good test to rank potential candidates for an RGD applications Flexibility is the way forward 16

Well defined acceptance criterion Good test to rank potential

17 Functional testing Once the material is RGD qualified, functional tests can be carried out Means to check sealability not RGD resistance Example: ISO Petroleum and natural gas industries Drilling and production equipment Wellhead and christmas tree equipment F.1.11 Pressure and temperature cycles F Thermochemical performance of seal materials 17

natural gas industries Drilling and production equipment Wellhead and christmas tree

18 Advice for qualifying seals for RGD service Beware of compound ageing Beware of aggressive fluids Changes in RGD behaviour? Compare material test conditions to field conditions if too dissimilar, repeat test in suitable conditions What about seal geometry? Is the standard O-ring representative of the system? 18

Compare material test conditions to field conditions if too dissimilar,

19 Thank you Materials Engineering Research Laboratory Limited Wilbury Way, Hitchin, Hertfordshire, SG4 0TW, United Kingdom T: +44 (0) F: +44 (0)

Guidelines the DNV way

Guidelines the DNV way for safe service elastomers in oil & gas Jon Huse Guidelines the DNV way for safe service elastomers Content: What is a DNV-guideline? Examples of DNV-guidelines - Qualification