Take a PEEK at a New Process

To meet Oil & Gas market requirements, a new cost-effective production method for large diameter seals, bearings and Back-up Rings over 600 mm / 24 inch and up to nearly infinite diameters has been developed at the Trelleborg Sealing Solutions facility in Helsingør, Denmark.

-By Jan Sklucki

PRODUCING CORNER REINFORCEMENTS OR BACK-UP RINGS for large diameter seals can be expensive. Usually, these kinds of seals are produced using billets of virgin PEEK material, formed using compression molding. “Compression molding can be a slow and complicated process. It requires large equipment, and though it gives options with different fillers and additives incorporated, it is very costly,” says Soeren Roepstorff, R&D Development Manager at Trelleborg Sealing Solutions in Helsingør.

With compression molding, if a new seal diameter is required, then a new, purpose-built mold tool is required. For PEEK materials especially, these molds must be made very accurately, incurring further cost increases and extending lead times for products. “All these factors together set us searching for a new solution,” says Lars Sondrup R&D Development Engineer at Trelleborg Sealing Solutions in Helsingør, who is the project manager for the development project.

Developing a New Solution

The new process solution was found by applying welding techniques to create a robust seal at a lower cost.

“A novel proprietary welding technique was developed especially for the welding of this material and the profile’s dimensions. This proved to achieve an impressive result” continues Lars. “The real skill is the combination of this new technique and our thorough research and development, determining the correct parameters to achieve an ideal weld. The PEEK materials high melting point creates this challenge.” But from extensive tensile and 3-point bending testing, Trelleborg Sealing Solutions has achieved very convincing results.

The seals can be produced in sizes from 600 mm / 24 inch to near infinite diameters, without the tooling costs associated with compression molding.

Convincing results have been achieved from extensive 3-point bending testing

Convincing results have been achieved from extensive 3-point bending testing

Zurcon® Z431

Zurcon® Z43 remains the preferred universal PEEK material for production of seals up to approximately 400 mm /16 inch because of lower friction and better material availability. However, for larger diameter seals, such as those required for FPSO vessels, Zurcon® Z431 has been specially selected. It can withstand the temperatures, pressures and loads exerted upon it during FPSO operation. The material does not degrade with time, is unaffected by most chemicals encountered in application and can operate in dirty environments without damage.

With NORSOK M-710 approval, Zurcon® Z431 fits the bill for use in the Oil & Gas industry FPSO vessels, especially where Zurcon® Z62 or other engineering plastics cannot be used due to temperature, pressure or legislation requirements, but its use is not just limited to this kind of application. “Though we’ve mainly designed this material and technique for the Oil & Gas industry FPSOs, really it’s suitable for any application with very high pressures and temperatures, and where high radial clearances are encountered,” says Soeren. “It can also aid manufacturers who are looking to reduce weight or save money on the cost of metals in production”

Performance in Application

Capable of performing with lubricating and non-lubricating fluids (dry running) and gases, as we ll as ceramic-coated surfaces, more applications are being considered or implemented already. “In addition to FPSO swivels, think split barges, hydropower dams, presses and flood barriers. There are a number of different areas we think we can apply this technique very successfully,” says Soeren.

After the welding process is complete, the resulting product is strong enough for machining, as is required for angled Back-up Rings. It is then combined with large dimension Turcon® seals to provide the same performance as compression molded seals, but with a lower price. “The combination of reduced costs and faster production and delivery make this a very competitive offering for the market,” finishes Soeren.

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Floating Production, Storage and Offloading (FPSO) vessels are floating facilities capable of separation and treatment of crude oil, water and gases while at sea. The capabilities are similar to that of a standard production platform. The oil is kept on the ship, while gas is used for powering the vessel – any excess is either returned to the reservoir or exported to the mainland. FPSOs enable deeper and more remote oil recovery operations and can remove the need for oil pipelines.

Technical Data for Zurcon® Z431Material characteristics, typical values
Pressure range:Up to 100 MPa at +150 °C
and up to 30 MPa at +200 °C
Tensile strength:90 MPa
Temperature range:-54 °C to up to +260 °CMelting point:+340 °C
Velocity lubricated:5 m/sGlass transition
+150 °C
Velocity dry:2 m/s bio-oils), phosphate
ester, water, air and others.
(Ball Indentation):
250 MPa
Media, gas:Dry running capabilityCoefficient of Linear
Thermal Expansion:
2.5 - 5 M/M x °K x 10-5
Chemical resistance:Very highElongation at yield:10%
Compliance:NORSOK M-710Elongation at break:25%
UV / sunlight resistance:High
Ozone resistance:High
Radiation resistance:10^9 Rad