- The pipe coating is designed to prevent the corrosive elements of the backfill from cominginto direct contact with the pipe steel.
- A coating may be deemed to have failed if any soil or water makes contact with the pipe steel.
- Some degree of coating failure is unavoidable and CP provides a particularly cost effective solution to this problem.
- A low level of coating defects and a fully effective CP system is, for most operators, a
normal and acceptable condition for an operating pipeline.
FUNDAMENTALS OF COATING
1. INEFFECTIVE CP : The commonest causes of ineffective CP are poor quality monitoring that fails to identify under-protection and extensive coating breakdown that creates a total current demand far in excess of the original CP design criteria.
2. CP SHIELDING : CP current is prevented from flowing onto
the pipe steel by a high resistance barrier, such as pipe coating that has lost adhesion to the pipe. This creates the conditions inwhich pitting and general corrosion occur and in anaerobic soil conditions the rate of corrosion attack may be accelerated by bacterial or microbial activity.
3. EXTERNAL DRIVERS: Electrical interference, stray current and galvanic effects can nullify the effect of the applied CP and create a corrosion problem where the pipe coating is defective. AC induced corrosion is most commonly associated with small coating defects.
4. STRESS CORROSION CRACKING: Stress corrosion cracking on buried pipelines is most commonly found beneath a coating that has become porous or has lost adhesion. Moisture must be present at the pipe surface but the critical potential for SCC initiation and growth is less negative than the commonly accepted protection potential of – 850 mV so CP shielding is a factor in SCC. Some degree of pressure cycling is required for axial crack growth.
USEFULL LIFE OF PIPELINE COATINGS
- COAL TAR ENAMEL : Coal tar coatings generally have a useful life of 25~30 years. Beyond this period, the coating resistivity falls to a level where it is no longer economical to protect pipelines with supplementary CP systems. Generally at this point, in case the
steel of the pipelines is good, end users look at a complete rehabilitation of the
pipeline to extend the useful life of the pipeline. - FUSION BOND EPOXY (FBE/DFBE) : FBE coatings generally have a useful life of 25 to 30 years. Beyond this period, the coating starts to blister and disbond especially in high water tables.
- THREE LAYER POLYPROPYLENE (3LPP) : 3LPP coatings have a useful life of 30 years. High temperature coating – tends to crack.
- THREE LAYER POLYETHYLENE (3LPE) : 3LPE coatings have a useful life of 50 years. Very stable coating. Tends to disbond from steel surface causing surface corrosion. Problem comes if there continuous access to moisture. Can lead to pitting corrosion. CP does not help. New technologies – EMAT are being developed to dectect coating disbondment.
External Pipe Coatings
The exterior of a pipeline is protected from corrosion with external pipe coatings. In contrast, the pipe’s interior is protected from caustic and abrasive fluids transported through it with internal pipe linings (linings).
As a result of the internal coating in the pipeline, friction is reduced in the pipeline, and, as a result, the flow rate is improved.
Pipelines are prone to corrosion, resulting in leaks, spills, and other mishaps with disastrous results. Numerous elements, such as oxygen, chemicals, and moisture, can contribute to corrosion.
The external coating aids in shielding the pipeline from harmful elements, reducing corrosion and lengthening the pipeline’s lifespan.
The external coating offers thermal insulation, abrasion resistance, impact resistance, and corrosion protection. These characteristics aid in shielding the pipeline from harm, ensuring the contents are transported securely and effectively.
Internal Pipeline Coatings
There are two types of internal pipeline coatings: those that improve hydraulic efficiency and control corrosion. As a result, flow coatings typically applied at 2 mils don’t qualify as corrosion-resistant linings, usually around 5 mils thick.
It is possible to install 100% solids at much thicker levels than water or solvent-based coatings, close to the gap between traditional flow and corrosion-resistant coatings.
The absence of water or solvent means that 100% solids can be used as internal pipeline coatings because they increase hydraulic efficiency and prevent corrosion.
Why is the Internal Pipeline Coating Important?
Internal pipeline corrosion can reduce pipeline capacity, product contamination, and leaks, resulting in significant economic losses, environmental damage, and safety hazards. Coating the inside pipelines with a protective layer helps prevent these issues by creating a barrier between the pipeline and the transported fluids.
Epoxy food grade Coating :
Potable Water Tank Coating Food Grade, 100% Solid epoxy coating. Pipes are coated internally to prevent corrosion and to improve the product flow characteristics. The company offers coating in the form of two-part liquid epoxy systems in thickness range from 75 to 500 microns. (High Build Coating system for Potable Water Tanks (overhead & underground), pipeline, reservoirs)
Epoxy food grade is a two component food grade, solvent free coating technology formulated with special grade resin, hardener, non-toxic pigment & additives designed for permanent water contact and are an effective seamless waterproof layer. It is used for handling potable water in Pharma, food, biotechnology and drinking processing or for any application involving carrying potable water lines. It can be applied on RCC / plastered surfaces after applying appropriate primer and of course on metallic pipelines / tanks after blast cleaning.
Advantages of Epoxy food grade application
Pipeline Coatings: Areas of Application
Protective Epoxy Coatings For Oil and Gas Pipelines
Current protective coating technology for oil and gas pipelines is recognized to have both technical and economic disadvantages. Many factors contribute to the complexity of designing efficient pipeline coating formulations; climate, properties of the substrate traveling through the pipeline, product flammability and rate of flow to name a few. In addition it must be taken into consideration if the pipeline is laid underwater, under ground or above ground and the coating must be formulated to provide long term internal and external durability, the coating must be formulated with some basic tenets in mind. Some factors contributing to the complexity of this industry are briefly addressed below.
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