Exceptional sour gas ratings for ED elastomers

The James Walker FR25/90 fluoroelastomer has been rated with an exceptional service life of 142,000 years in a sour (H2S) gas and liquid hydrocarbon mixture, during qualification for Norsok M-710

The James Walker FR25/90 fluoroelastomer has been rated with an exceptional service life of 142,000 years in a sour (H2S) gas and liquid hydrocarbon mixture, during its qualification to the exacting requirements of Norsok M-710.

Two further grades have already achieved Norsok qualification - fluoroelastomer FR58/90 with a predicted service life of 817 years under test conditions, and hydrogenated nitrile Elast-O-Lion 101 with 36.7 years.

The FR25/90 sour gas life prediction, combined with a zero-defect rating in explosive-decompression (ED) resistance tests, gives it a head start for low-temperature sealing duties across the oil and gas sector.

Explained Trevor Clarke, James Walker global director for oil and gas operations: "Accelerated ageing tests make it possible to compare the relative service lives of different types and grades of elastomer under sour gas conditions - providing a valuable guideline for users.

"The life predicted for FR25/90 under laboratory conditions is very unlikely to be achieved in oil and gas field operations, but it does indicate exceptional resistance to the fluid media".

Developed by the Norwegian petroleum industry, Norsok M-710 features a tough testing regime for non-metallic sealing materials used in oil exploration and production.

It combines rapid gas decompression tests for ED-resistance with the evaluation of sour gas ageing.

Service life in sour gas was predicted for each elastomer, under Norsok test conditions at 80C, as the time before its tensile strength was halved.

To obtain the figures, the Materials Engineering Research Laboratory (MERL) exposed material samples to a fluid containing H2S for different lengths of time up to 40 days, at a set pressure and a variety of temperatures.

Samples were physically tested to different parameters as soon as they left the sour gas test rig.

The working life was extrapolated from the resulting time-based curves using Arrhenius techniques.

When used in this manner, Arrhenius is a good tool for comparing the relative service lives of different elastomer types and grades.

The DNV-witnessed rapid gas decompression (RGD) tests for ED resistance were carried out by James Walker Technology Centre - which has a custom test facility specifically for this work.

'O' rings in these materials were housed and soaked in a mixture of carbon dioxide and methane gases for 72 hours at 150bar and 100C.

They were then subjected to ten ED cycles (rapid decompression, dwell for one hour at 100C, recompression and hold for 24 hours) before being microscopically examined and rated for cracks, holes and blisters.

FR25/90 is widely used for ED-resistant seals in the oil and gas sector - down-hole, at the wellhead and in upstream pipelines.

It maintains high integrity sealing capability down to -30C (-22F).

FR58/90 and Elast-O-Lion 101 are renowned for their high integrity fluid sealing capabilities in the oil and gas sector.

In addition to ED-resistance, FR58/90 displays excellent chemical and thermal properties; Elast-O-Lion 101 also has exceptional mechanical strength and wear resistance.

All three elastomers are nominal 90 IRHD compounds, with the excellent resilience and low compression set characteristics needed for efficient long-term fluid sealing.

"The extended low temperature capability of FR25/90 enables it to work efficiently in colder environments and/or at higher pressures than our other Norsok M-710 qualified elastomers", confirmed Trevor Clarke.

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