Field joint coatings Heat Shrink Sleeves 100% Solvent less Liquid - - PowerPoint PPT Presentation

Field joint coatings

• Heat Shrink Sleeves
• 100% Solvent less Liquid Epoxy
• 100% Poly-urethane
• Tapes

Rehabilitation Coatings

Escavation and removing the old Coating

Shot Blasting X-ray Inspection of Blasted Pipe

Blasted Pipe Pipe being Coated

TWO COMPONENT SPRAY MACHINE

TAPES / WRAPPERS

Internal Coating

Pipeline Failure Incidence by Cause

Cause % of Total Internal Corrosion 6 External Corrosion 13 Damage 33 Construction/operation related 9 Accidental 7 Other (defective materials) 32

How we define Pipeline Failure

• According to Dennis Neal

“An underground coating is failed when it is no longer economical to maintain Cathodic Protection”

• NACE RP169-83 states:

Satisfactory service is indicated if no significant current increase attributable to deterioration of the coating has been required to maintain adequate CP.

Usual Factors Which Cause Coating Failure

• According to Peabody, “Coating alone can

control pipeline corrosion only if it is an effective insulator, after the backfilling is

• completed. However, since coatings absorb

moisture, the electrical resistance drops down and they conduct some current. Thus there are some holidays after insulation and CP tries to take care of this damage.”

All Ageing Pipelines Show

• Cathodic Disbonding
• Water absorption

– Osmosis, Electroosmosis or Electroporesis

• General loss of bond and blistering
• Leaching of components
• Cold Flow
• Damage from Soil Stresses
• Shielding Effect

– Stress Corrosion Cracking – Pitting

Summary

• Surface Preparation and cleanliness is the most

important step for the long life of the coating.

• Pre-treatments have been found to enhance the

cathodic disbondment resistance considerably.

• Choice of coating – under Indian conditions 3

Layer PE is best suited.

• Handling is required carefully to avoid coating

damage.

Coatings for Corrosion Prevention for Reinforced Structures Concrete Structures

A.S.Khanna

Corrosion Science & Engineering IIT Bombay

Some Concerns!

Do the present sea-links in Bombay would survive for the planned life? Are many flyovers, being built or built recently, will remain distress free for the planned life? Is the corrosion protection technology used for these structures is O.K?

Requirements of Sustainability of a Concrete Structure Can withstand normal seismic activity ( Richter scale 5-6). Not affected by strong winds, hurricanes, rains. Stable to dynamic loading Not affected by high humidity and pollutants in the environment.

Though, basic concrete design incorporates most of these factors, deterioration of concrete structure by external factors is posing a great threat.

External threats are basically :

Moisture ( High Relative Humidity), Pollutants like chlorides, sulphur dioxide, carbon dioxide, whose continuous ingress into the concrete degrades the concrete resulting in initial deterioration and finally collapse

• f structure.

The biggest threat is to coastal buildings, bridges, flyovers and jetties. How this problem arises and what are the solutions

Why Rebar Corrodes?

Rebars are mild steel rods embedded in concrete to increase its tensile strength. Initially these steel rods are in passive state due to basic environment of lime in the cement. With time chlorides, carbon dioxide, sulphur dioxide, oxygen and moisture penetrate and when sufficient quantity of such materials reaches steel/concrete interface, passivity is lost and corrosion of rebar starts, forming voluminous products and thus cracking/peeling the plaster.

Poubaix Diagram Showing the Stability of Steel Rebar in Concrete

How can this be stopped?

Use of Good raw materials. Proper maintenance Better concreting practice Using appropriate corrosion protection technology.

What are the corrosion protection Technologies

Using modified steel – TMT or CRS Steels Stainless steels FRP Using Protective Coatings. Using admixtures in Concrete.

. Using migrating inhibitors.

Using Cathodic Protection

Steel with modified Microstructure

TMT STEEL

Alloy Steels Bars

C Si Mn P S Cu Cr Ni V Nb

ASTM Weathe ring Steel

0.19 (ma x) 0.30

• 0.65

0.8 – 1.35 0.04 0.05 0.25

• 0.40

0.40

• 0.70

0.40 (ma x) 0.02

• 0.10

TISC O CRS

0.18 0.45 1.0 0.12 0.05 0.3- 0.5 0.5- 0.8

• SAIL

0.20 0.30 1.2 0.06 0.04 0.35 max

• Cu

+Ni 1.40

• USSR

0.12 0.47 0.47 0.04 0.04 0.2- 0.4 0.6- 0.9 0.3- 0.6

Franc e/Balg ium

0.15 Cr 0.28

Si + Mn + Cr + Ni + Cu = 2.40

Comparison of Corrosion rate of a plain steel with improperly alloyed steel bar

Stainless steels

What kind of Stainless Steels are being talked for Rebars ?

• Min. 11.5% additional Cr

Ferritic Stainless Steels

• 18% Cr and 8% Ni

Austenitic Stainless Steels

• More than 18% Cr less Ni- ~50% Ferrite and

Austenitic phase

Duplex Stainless Steels Martensitic Stainless Steels PH Stainless Steels

Corrosion Problems in Stainless Steels

• Pitting and Crevice

 PREN = %Cr+3.3(%Mo+0.5W)+30N

• Stress Corrosion Cracking
• Passivity
• Weld Decay

CRS 100

• Microstructure
• Mechanical testing
• Chemical Composition
• Corrosion Test
• Pullout Strength

A detailed testing of CRS100 Rebar was carried out at IIT Bombay to find its suitability in Indian Conditions.

Microstructure of the CRS BAR

Test Report of CRS 100 Ferritic Stainless Steel

Pullout Strength :

Cylindrical Concrete blocks of diameter 4 “ and length 8 “ were made to test the pull out strength of the 16” dia rebars. Cover thickness was kept 61/2”. The concrete used was M25. Result of pull out with curing time are given below

Immersion Test in various Solutions

100

Life Cycle Cost of Ferritic Steels ( CRS 100)

Fiber Reinforced Plastic Rebars

Versatile No corrosion problems Costly Relatively less common in big projects

Inhibitors in Concrete

Various kinds of inorganic and organic chemicals can delay the onset of corrosion initiation and control the rate of corrosion either by stabilizing the layer of

• xide film or by forming physical barrier between the

environment and reinforcement.

• Admixtures in the concrete mix which remain

distributed in the bulk of concrete cover.

• Mixed in the concrete as admixtures in the beginning

and with time migrate to steel concrete interface and form a thin barrier layer just like a coating.

• They can also be sprayed on rebars just at the time of

pouring concrete on the RCC cage.

• They also can be added to a readymade structure

where signs of cracking are just appearing.

Two kinds of inhibitors for concrete structures :

Admixtures

Inorganic compounds : Calcium Nitrite, Calcium nitrate, Sodium Metasilicate, Lithium Nitrate (LN), Microsilica, Organic based Corrosion Inhibitor : Aminoethylethanolamine (AMA), di-Sodium -glycerophosphate (BGP):

Migrating Inhibitors

Protection of rebar by Inhibitor

MIGRATING INHIBITORS

Coatings for Rebar

COATINGS FOR REBARS

• Cement slurry
• Cement Polymer Composite coating

Cement based Coatings

• Liquid Epoxy Coatings
• Fusion Bond Epoxy Coatings

Epoxy Based Coatings

• Polyurethane coatings
• Polysulphide coatings

Other Coatings

Bending of Liquid Epoxy Coated Rebar

Bending of FBE Coated Bars

Bending of PVB Modified Liquid Epoxy

1% PVB 0.5% PVB 2% PVB

Dual Fusion Bond Epoxy coated bars

Coated sample Bare rebars

SAMPLE AFTER BEND TEST

Showing no cracks

SAMPLE AFTER IMPACT TEST

Point of impact

Pullout Strength of various Rebar Coatings with M20 Concrete for 16 mm bar

Type of Coating Mean Load (ton) % Bond Strength Bare Rebar 8.13 100 Rebar with FBE 7.07 87 Liquid Epoxy 5.27 64 Dual Epoxy 9.25 113 LE + 1% PVB 6.88 84.6 LE + 2% PVB 6.39 78 Polysulphide 5.52 69.8

Combination of Inhibitors with other technologies

TMT + Migrating Inhibitors 5-7 – 15-17 years CPCC + Calcium Nitrite 6-8 - 16 -18 years FBE + Migrating Inhibitors 7-9 – 20 years FBE + Migrating inhibitors + Silica fumes 20-30 years Dual FBE + Migrating Inhibitors + Silica Fumes 30-50 years Stainless Steels 60-100 years

Conclusions

Stainless Steel, especially cost effective Ferritic Stainless are the best Choice. Dual Fusion Bond Epoxy is second best . All other technologies be used in combination. Coatings on rebars / TMT bars/ CRS bars if combined with MCI or other inhibitors can prolong the life of the concrete structure. External coating of concrete structure very much helps in reducing the corrosion due to very low ingress of pollutants/moisture.