Insulating Sets – What are they used for?

The insulation set is used as a means of preventing corrosion in pipework. The basics of corrosion can best be determined by viewing this as an electrical reaction between an Anode (-) & Cathode (+). In a battery the Anode is an unstable group of electrons (or the more unstable element) which want to pass to the Cathode (the more stable/inert). However an electrolyte prevents the passage of electrons. The insulating gasket / sleeves & washers (preventing metal to metal contact) are similar to the electrolyte in that it prevents the passage of electrons between 2 metals. When a conductor meets both anode & cathode, the electrons are allowed to pass between & an electrical circuit is caused.

There are 2 types of corrosion:

1. Cathodic – which is where a metal oxidizes due to the fluids it is in contact with. Cathodic protection between flanges reduces the movement of electrons along the pipework & therefore slows down the rate of corrosion in pipework. The high salinity (high salt content) of fluids in the Middle East leads to a major problem with stress corrosion & crevice corrosion.

2. Galvanic corrosion – is most similar to the battery in that when in direct contact i.e. 2 metal flanges of different materials (316L vs Carbon Steel) the anode or less inert (Carbon Steel) will deposit electrons on the steel & therefore oxidize rapidly. Again a highly saline environment accelerates this, typical of Hydrogen Sulfide H2S (aka Hydrosulfuric acid / Sewer Gas / Sour Gas). As a weak acid it is corrosive.

By insulating the flanges both cathodic & galvanic corrosion is slowed down.

Corrosion is the oil & gas industries biggest maintenance cost – If a user can extend the life of pipework by fitting insulating sets the price of the set is very small in comparison to the cost of replacing the complete pipework assembly.

 

History : PHENOLIC

The earliest use of insulating sets started with Phenolic resin (see attached data sheet).

We use only Fabric based laminate Phenolic – other competitors use paper based, which is even weaker.

The electrical grade of material is designated by National Electrical Manufacturers Association (NEMA). Our grade is CE.

However generally it has some limitations as a gasket material:

·         It is very brittle – flexural strength: 110 MPa

·         Wicks (like a cotton wick used in a fluid, the penetration through the gasket is high)

·         Low strength – Tensile strength: 75 MPa – this makes it unsuitable for higher pressures & is not used above 300# (psi) flange ratings.

·         Low temperature limit – 115 Celsius.

SMITH manufacture all types of phenolic insulation sets.

 

Neoprene faced Phenolic

With all gaskets the bolt torque required to make a seal can be reduced by adding a very thin layer of neoprene rubber. However the limitations of Phenolic still remain.

Phenolic & Neoprene faced phenolic insulating sets still remain popular within industry.

 

Fibre Gaskets / PTFE

PTFE is a good insulator & as the introduction of Modified PTFE has improved the cold flow characteristics (PTFE under torque acts like a plastic & flows, unlike rubber which has good recovery) it makes a good gasket & therefore has been often specified for the same.

Some grades of Fiber gasket material with insulating properties, such as Aramid, Glass Fibre & Rubber fillers also show similar insulating properties. However we recommend TEFLON / PTFE over fibre gasket materials due to their inherent non-stick properties. PTFE materials are good for high temp applications up to 300 Celsius at low pressure (ASME 150#).

 

Type LP: Glass Re-inforced Epoxy (GRE) Resin

GRE is used as an engineering plastic with good strength & temperature characteristics.

The industry generally calls for G11 or G10 National Electrical Manufacturers Association (NEMA) grade material.

The Corrosion Control System type LP uses G11 material as a base & utilizes a rubber or PTFE O-ring/gasket within a groove to minimize the bolt torque requirement to seal. As G11 is very stiff, it needs the small seal to overcome the sealing limitations. However the level of sealability by the end user may not be very high, hence we supply gaskets without the seal ring (Type UP). G11 has a relatively high temperature limit than G10 (150 C). However it is used only to counter the weaknesses of Phenolic resin & can be used for flange ratings up to 300#.

G11:

·         It is very strong – flexural strength: 490 MPa

·         It does not wick.

·         High strength – Tensile strength: 220 MPa – this makes it unsuitable for higher pressures & is not used above 300# (psi) flange ratings.

·         temperature limit – 155 Celsius.

 

Type HP: Glass Reinforced Epoxy with Steel core

The Corrosion Control System type HP uses an insulation set with steel core to directly replace RTJ’s due to the strength of G10 combined with a steel core. The groove within the steel core provides a pressure balancing effect, combined with the spring energized PTFE seal ring such that it prevents any blow-out of the laminate, whilst also maintaining a seal under cryogenic conditions (flanges contract & flange loads are reduced under sub-zero conditions due to bolt contraction).

An additional effect is that the geometry of a flat gasket is far easier to seat than a RTJ, so it can be used to directly interchange an RTJ, particularly when flange rotation is a risk.

G10:

·         It is very strong – flexural strength: 482 MPa

·         It does not wick.

·         High strength – Tensile strength: 320 MPa – Higher strength than G11.

·         temperature limit – 120 Celsius.

New designs are being introduced to the market such as Fire-safe designs to meet the API 6FB fire safe test.  SMITH are constantly testing new designs to meet specific customer requests.