Field joint coatings • Heat Shrink Sleeves • 100% Solvent less Liquid Epoxy • 100% Poly-urethane • Tapes
Rehabilitation Coatings
Escavation and removing the old Coating
X-ray Inspection of Blasted Pipe Shot Blasting
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 9 related Accidental 7 Other (defective 32 materials)
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 of 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 0.8 – ASTM 0.19 0.30 0.04 0.05 0.25 0.40 0.40 0.02 Weathe - 1.35 - - - ring (ma (ma Steel 0.65 0.40 0.70 0.10 x) x) TISC 0.18 0.45 1.0 0.12 0.05 0.3- 0.5- - - O 0.5 0.8 CRS SAIL 0.20 0.30 1.2 0.06 0.04 0.35 - Cu - max +Ni 1.40 USSR 0.12 0.47 0.47 0.04 0.04 0.2- 0.6- 0.3- 0.4 0.9 0.6 Franc 0.15 Cr 0.28 e/Balg Si + Mn + Cr + Ni + Cu = 2.40 ium
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 ? Ferritic Stainless • Min. 11.5% additional Cr Steels Austenitic Stainless • 18% Cr and 8% Ni Steels Duplex Stainless • More than 18% Cr less Ni- ~50% Ferrite and Austenitic phase 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 A detailed testing of • Microstructure CRS100 • Mechanical testing Rebar was carried out at • Chemical Composition IIT Bombay to • Corrosion Test find its • Pullout Strength 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
Life Cycle Cost of Ferritic Steels ( CRS 100 ) 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 oxide 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. Two kinds of • Mixed in the concrete as admixtures in the beginning and with time migrate to steel concrete interface and inhibitors for form a thin barrier layer just like a coating. concrete • They can also be sprayed on rebars just at the time of structures : pouring concrete on the RCC cage. • They also can be added to a readymade structure where signs of cracking are just appearing.
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 based • Cement slurry • Cement Polymer Composite coating Coatings Epoxy Based • Liquid Epoxy Coatings • Fusion Bond Epoxy Coatings Coatings Other • Polyurethane coatings • Polysulphide coatings 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 % Bond (ton) 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.
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