Highly reliable fire-resistant insulating flange seals.

Highly reliable fire-resistant insulating flange seals.

Highly reliable fire-resistant insulating flange seals

It can only be added that the more severe the conditions in which the seal operates, the greater the likelihood of its damage and the more serious the consequences. And in this context, in our opinion, of particular interest is the fire-resistant combined disc seal GERDA-VCFS “Pikotek”, which provides reliable tightness and electrical insulation of flanges at high pressure, high temperature and aggressive environment, maintaining operability even under conditions of direct exposure to flame.

The GERDA-VCFS “Pikotek” sealing technology is based on the standard VCS design, which was originally developed by the American company Pikotek to ensure reliable sealing and electrical insulation of critical connections operating in the most severe conditions (VCS = Very Critical Service), especially where RTJ flanges with phenol-formaldehyde resin sealing rings were used, which often failed. The VCFS (FS = Fire Safe) design was created by supplementing the basic design with a secondary fire-resistant sealing element, which ensures the tightness of the connection at temperatures up to 815°C.

The VCS seal design (Fig. 1) is based on a stainless steel support disc coated with an insulating glass epoxy coating that has high mechanical and electrical strength, low water absorption and an operating temperature of up to +200°C. Each side of the disc has a concentric groove machined into which a spring-loaded dovetail-shaped Teflon sealing element is installed. This element creates an impermeable barrier for liquid and gas across the entire thickness of the coating and provides a self-sealing effect, when the tightness of the connection increases with increasing internal pressure in the joint. Such a highly reliable sealing system allows the VCS to be used at operating pressures of up to 70 MPa.

Fig. 1 Basic VCS seal design

In addition to excellent sealing properties, the VCS design provides reliable electrical insulation of the flanges, which prevents corrosion that usually develops in the pipeline due to contact between dissimilar metals and stray currents. When used in combination with special insulating sleeves and washers for connecting bolts (Fig. 2), the VCS can serve as an effective insulator in pipelines with a cathodic protection system.

What makes VCS unique among other electrical insulating seals is its strength and durability. Traditional insulating gaskets are quite fragile and prone to damage, as they are made of brittle non-metallic materials. The steel carrier disc and well-thought-out patented design allow VCS to withstand significantly higher pressure, cyclic loads, bending moment, excessive tightening torque of threaded connections and other installation errors.

Fig. 2. Installation of VCS with an insulating kit

The use of VCS seals on high-pressure pipelines, where RTJ flanges are traditionally used, allows solving such problems inherent in this type of connections as corrosion of the flange surface due to contact with the working medium and destruction of the sealing ring cavity due to the concentration of the entire load in this area.
Fire-resistant disc seal GERDA-VCFS “Pikotek”

combines the positive qualities of VCS technology with a new technical solution that allowed this seal to successfully pass the fire resistance test in accordance with the requirements of the 3rd edition of API 6FB.

Unlike the standard VCS design, the GERDA-VCFS “Pikotek” seal has two sealing elements (Fig. 3):
primary — made of spring-loaded Teflon and secondary — in the form of a corrugated ring made of Inconel alloy with an electrically insulating coating.

Fig. 3 VCFS seal design

The corrugated ring serves as a secondary (backup) seal under normal operating conditions and as a primary (main) seal — during a fire. Together with the secondary sealing element, a square steel ring with an electrically insulating coating is installed, which eliminates excessive compression of the corrugated ring during a fire when the disc coating is destroyed.

Thanks to this double seal, VCFS provides fire resistance, increased reliability and requires less bolt tightening force than other types of seals.
Insulating washers for VCFS seals are made of hardened carbon steel, which is coated with a special non-conductive coating. Such washers do not break down under the influence of flame, which prevents the loosening of the flange connection during a fire.
VCFS can operate at pressures up to 42 MPa (taking into account fire resistance) and is offered for flanges with a connecting protrusion with a diameter from DN 50 (2”) to DN 600 (24”), as well as for RTJ flanges with a diameter from DN 150 (6”) to DN 600 (24”).

___________________________________________

Dunaev A.A. Head of Department, CJSC NPP Gerda