Why Pipeline Coatings Pipelines are made of steel. They pass - - PowerPoint PPT Presentation

Why Pipeline Coatings

• Pipelines are made of steel.
• They pass through various soils, rivers, ponds, marshy

lands etc.

• Each of these terrain has different extent of corrosion

which can limit the life of pipeline.

• In addition, soils also have bacteria.
• Thus it is required to protect the pipe outer surface from

corrosion and bio-degradation.

• Inside of pipeline also corrodes, however, it depends

mainly from the quality of fluid, whether it is sour or sweet.

• A sour environment ( with H2S more than 500 ppm)

usually corrodes the pipeline. However, due to other

• ption of using inhibitors, coatings are seldom applied.
• However, anti drag coatings are usually applied on inside
• f pipe.

Critical issues in the Protection

• f pipelines
• How oil pipelines differ from other lines
• Types of coatings – important properties

– High performance – Low permeability – High Dielectric constant – High Impact strength – High Cathodic Disbondment

• Field joint coatings
• Rehabilitation coatings

Coating Types

• New Pipelines

– Coal tar – Fusion Bond Epoxy – Three layer PE – Tapes

• Rehabilitation

– Tapes – Liquid Epoxy – Liquid Poly-urethane

• Cathodic Protection

History of various line-pipe coatings

3 layer PE

Coal Tar Coatings

• Possess

continuity, hardness, adhesion, and corrosion resistance.

• Are less expensive.
• If complimented by a suitable cathodic protection

system, they can give longer life.

• Poor impact resistance.
• A wide temperature change often causes the surface

to crack.

• However, due messy conditions at coating yard and

fear carcinogenic vapour emitting, coaltar based epoxies are phased out in west.

• In India also, a lot of coal tar coatings are being

replaced by alternative coatings

Fusion Bond Epoxy Coating

Single layer Coating

• Surface finish SA21/2
• FBE coating thickness 350-

400 um

• High Cathodic

Disbondment

• High Impact Strength

(<10 J)

Why Fusion Bond Epoxy?

• Long track record and experience
• Better Corrosion resistance,
• Lower thickness
• Relatively easier application,
• No chance of missing coating
• High Resistance to Cathodic Disbondment
• No Shielding effect and SCC or Pitting

Schematic of Fusion Bond Epoxy

Shot Blasting Pre-heating Powder Coating Quenching Quality Check Transportation

Limitations of FBE

• Handling is difficult

Transportation Backfilling Improper storage

Three Layer PE Coating

• Surface finish SA21/2
• 100-150 um FBE primer

coat

• 200 um Adhesive Coat
• 1500 – 3000 um PE coat
• Good Cathodic

Disbondment

• High Impact Strength ( 15 J)

Schematic of Three layer PE Coating

Shot Blasting Pre-heating Fusion Bonding

• f Primer Epoxy

Quenching Quality Check Transportation Adhesive coat & PE Extrusion

Three Layer PE Coating

Coating Conditions

• Primer layer is applied by spraying

electrostatically charged epoxy powder on heated

• pipes. The temperature should be within 190-

220oC.

• Adhesive layer which is a polyolefine is applied

before the gel time of the epoxy coating. Its temperature about 220-230oC. The main function

• f the coating is to bind the primary epoxy and the
• uter PE
• On the Adhesive coated layer the PE is extruded
• ver it. Its temperature is maintained at 238oC.

Powder Coating of Epoxy Extrusion Coating of Adhesive & PE Checking the Holidays

Mechanism of 3 Layer PE System

Relationship between temperature of Epoxy coating and the time of adhesive coating

Application Window

180 200 220 240 20 40 60

Pipe Temperature

Time before application of adhesive

Is there any problem with 3 Layer PE?

• Not really - These coatings are one of

the best coatings, however factors such as Their higher Cost Missing of FBE and/or adhesive coat. If proper care is not taken one can Repair is very costly compel to see alternatives

Indian Scenario

• All pipelines buried in early fifties were either

bare or coated with coal tar.

• Coaltar was applied over ditch and it used to fail

in aggressive environment – surface preparation and cleanliness was poor.

• First major pipeline eracted by GAIL Inia in 1985

( 2000km) was chosen as 3 layer PE.

• Today 3 LPE is major metho, a few pipelines by

FBE and still a large number by Coal-tar.

HBJ Pipeline Vijay Pur

3 Layer PE Coating Field Joint Coating

36” Pipeline Hazira 3Layer PE

3 Layer PE Coating Across Sabarmati River

Microstructure of dual FBE Coating

Effect of dual coating thickness on Cathodic Disbondment Resistance

FBE Coatings – Effect of Powder type

• n Impact Damage Resistance

350 um 350 um 500 um 500 um 500 um

Coating Economics

Cost of Coating is typically 3-5% of the total project cost. – Choice of Applicator Location – Lower transportation and handling cost when it is close to site. – Selection of coating – a poor coating can run the risk of increasing construction cost, due to more repairs and delay in the project – Variation in thickness – Permeability and dielectric constant – Cathodic disbondment – Impact and abrasion – Testing of raw materials and Inspection during coating and installation – Custom duty and FE variation ( under Indian conditions)

Expenses during various categories for pipe coating

Item % of total cost Right of Way(Survey, clearance, damage) 2-5 Materials (other than coating) 35-50 Labour 35-50 Engineering / inspection 3-5 Pipe Coating 3-5 Taxes / Transportation /legal 10-15

Relative application cost comparison for different Line Pipe Coatings (Ref. JPCL, Vol. 17, July 2000) Indian scenario – 3 LPE is cheaper than Single or dual FBE

Rehabilitation Coatings

Escavation and removing the old Coating