The growth of long distance underground pipeline systems increases the need for special protective measures against external corrosion. The aggressive nature of the ground, the effect of stray currents from nearby installations and the damaging potentials created by electro chemical reaction in the earth have a deterioratory effect on pipelines and demand reliable long term corrosion protection measures.
Experience during recent years has shown that the cathodic protection together with a high grade passive corrosion protection by application of coating on the pipeline, provides a most efficient and economical solution.
Insulating joints at the flange points in a pipeline have a very important part to play in reducing the cost of the cathodic protection systems.
Application of Flange Insulation kits
- To limit the extent and cost of cathodic protection current to only those pipes that need to be protected from the main cathodic protection system.
- To electrically "split up" long pipelines into distinctive cathodic protection systems.
- To isolate a pipeline to ensure that cathodic protection or stray electricity currents do not cause increased corrosion, or cause a hazard.
- To isolate piping systems where dissimilar metals are present.
- To eliminate static loading charge transfer in discharge or loading operations at oil storage terminals.
Types of Kits
Insulating sets are generally available in three types, depending on the flange configuration . Each set comprises of one central gasket either flat or oval ring type joint section depending on flange type, one full length insulating sleeve per bolt, two insulating washers and two back-up steel washers per bolt. The steel washer is provided to protect the insulating washer from damage by the nut.
It is recommended that for complete protection a self adhesive tape be wrapped around the outside of the flange to prevent the ingress of conducive foreign material.
- Type D gaskets are designed to fit into the grooves of ring-type-joint flanges.
- Type E gaskets are designed to fit flat faced flanges.
- Type F gaskets are designed to fit raised face flanges.
One piece integral sleeve and washers are also commercially available. The isolating washers and steel washers are generally 1/8" or 3.2mm thick.
Materials
- For flat gasket commonly used materials are reinforced phenolic laminate, either plain or neoprene coated. OR
High grade electrical quality compressed asbestos fibre. - For ring type central gasket commonly used material is reinforced phenolic laminate.
- For sleeves and washers commonly used material is reinforced phenolic laminate.
Sleeves are available in following materials:
Mylar, Polyethylene, Phenolic, Silicon Glass, Epoxy Glass etc. Polyethylene is suitable up to 66°C, Phenolic up to 107°C and Mylar up to 180°C.
Neoprene faced phenolic gaskets are widely used for insulation in the Gas and Oil industry because the soft neoprene rubber provides good sealing qualities. Gaskets made from asbestos sheet are specially formulated to provide good electrical insulating properties. They are used in applications where very large diameter flanges are used.
Applicable Standards
- BS 2572 - Specification for Phenolic laminated sheet and epoxy cotton fabric laminated sheet.