Event focuses on high temperature elastomer seals

Raw material manufacturers criticise presentation of test results at the Fifth International Oilfield Engineering with Polymers Conference in March in London.

The Fifth International Oilfield Engineering with Polymers Conference, jointly organised by MERL and Rapra Technology, from 29th to 30th March 2006 in London, attracted delegates from 18 countries.

The conference was primarily focused on high temperature elastomer seals with other papers covering insulation coatings, new resin systems and hoses.

In the initial paper by BP Exploration, Steve Groves said the industry needed to respond to increased demands due to exploration in very deep water.

Temperatures are likely to increase from 150 to 250C and pressures are rising from 1000 psi to 1700bar.

To meet the demands: thermal barriers are being used to permit lower temperature performance materials to be used; material limitations are being studied; and better testing and modelling is being carried out, more representative of service.

In terms of understanding the limitation of current materials, it is no longer appropriate to select materials based on their generic polymer type alone.

Seals Eastern, for instance, presented a paper that demonstrated that the cure systems used for Aflas grades can significantly affect the chemical resistance to potassium formate.

In addition, material selection based on the standard compatibility tests (change in tensile properties, volume and hardness) does not give the same ranking in performance as tests which are closer to the service conditions, such as stress relaxation, compression set and explosive decompression.

There was criticism from the raw material manufacturers regarding the presentation of test results in some papers.

In some cases the polymer grade was not strictly defined and the desire to present comparative data did not take into account the upper operating temperature limit of the polymer.

Specification limits and standards were raised as a discussion point.

Some designers have issues with the chemical resistance limits, for example as specified in Norsok M-710, since they do not relate to service conditions.

The limitation with standards was demonstrated in a paper by Parker Hannifin which identified that although there are numerous hose specifications, none include the high temperature and high pressure hoses currently being demanded.

The UK Health and Safety Executive has been active in promoting safe practice of work in the offshore industry and has been working with Merl and the BHR Group.

A report is available called: "Elastomers for Fluid Containment in Offshore Oil and Gas Production: Guidelines and Review".

At the conference, Robert Campion from Merl gave a comprehensive overview of the report with case studies on the failure modes of elastomeric components (seals, hoses, packers and plugs).

Guidelines will shortly be issued to understand explosive decompression or rapid gas decompression (RGD) and how to avoid the problem.

The primary material properties required are high modulus and high elongation at break.

Further work is being carried out by the BHR Group to develop a predictive tool based on biaxial strain as a criterion for failure.

Permeability measurements are generally restricted to one gaseous phase.

A paper by Marie-Helene Klopffer from the Institut Francais du Petrole examining the permeability of mixed gases found a lower than expected permeability for CO2 and CH4 in plasticised polyvinylidene fluoride which was not the case for HDPE.

A further paper on the subject by Zoltan Major from the University of Leoben, Austria, also found that the permeability of CO2 and CH4 was lower than expected for more polar materials.

RGD is also a function of product quality; failure can initiate from large agglomerations or voids in the material.

The raw material suppliers presented papers on grades that are relatively new to the market.

Ticona presented a modified linear PPS grade which was claimed to out perform PA11 and PVDF at higher temperature.

DuPont International described Pipelon, a fluoropolymer coating for down-hole tubing with better performance against H2S than epoxy.

In addition it was found to have good asphaltene scale resistance enabling longer service life.

The drawback is that the material can only be applied under factory conditions.

Lanxess presented Therban HT; combined with a new additive package and full hydrogenation, the upper operating limit can be increased to 160C.

Support was being offered to the oil industry for compound design as the hydrogenation level, ACN content and cure system needs to be tailored to meet the demands of the application.

Solvay Solexis presented a FKM Type Five (based on the ASTM D1418 nomenclature and description of fluorinated elastomers).

Base resistance has been improved by introducing branching and ethylene in the polymer architecture.

The material now provides a balance in chemical resistance for aromatic hydrocarbons, oil, methanol, H2S, steam and amines with good low temperature (below 0C) performance.

Shin-Etsu Chemical presented a Sifel range of perfluoroelastomers.

Unlike other fluoroelastomers, the material is not limited to gum compound for compression moulding but can be formulated in liquid injection mouldable grades adhesives, coatings and potting gels.

Apart form the processing versatility and inherent chemical resistance, the polymer has good low temperature performance (TR10 at -50C) and high electrical insulation resistance.

Improvements in modelling techniques were evident from presentations by ERA Technology and Dunlop Oil and Marine.

Alan Friday from ERA presented a paper that described the electrical and thermal modelling techniques that can be used to evaluate umbilical designs.

The depth of work carried out by Dunlop Oil and Marine to predict and validate the fatigue life in offshore marine hoses was impressive.

This has enabled the firm to offer hoses in medium- to deep-water applications with a design life of 200 years and 20 years for metallic and non-metallic parts respectively.

Proceedings are for sale through the Rapra bookstore.

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