Delhi sabnis corrosion termarust on crevice corrosion (1)
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Crevice Corrosion & Pack Rust: A Serious Structural Problem
By
Gajanan M. Sabnis, PhD, P.E.
Emeritus Professor, Howard University, Washington, DC.
(gms@sabnis.com)
Crevice Corrosion & Pack Rust
A Serious Structural Problem
ByCraig A. Ballinger,
P.E. Termarust
Technologies
Today’s Presentation
• Initial Comments
• Introduction to Repair/rehab/ concept and role of corrosion mitigation
• What are the affected areas? Reasons and result with visual observations and effects
• What is different in the procedures of conventional vs. the new one (sandblasting vspressure water cleaning) and paints
• Why is procedure of cleaning better not for our reason but also for environmental reasons
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Today’s Presentation(continued)
• Initial Comments
• Future practice and maintenance/rehabilitation
• Life cycle cost analysis
• Overall savings
• Case studies for bridges and other structures
• Conclusions
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What is Crevice Corrosion and what is Pack Rust?
Why are they important?
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Crevice Corrosion Can be Stoppedwith
Active High Ratio, Co-Polymerized,Calcium Sulfonate Coating System
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Many old truss bridgeshave not been painted
because engineers and owners know that
• Film forming paints do not last long over connections with crevice corrosion and pack rust
• Painting does not stop loss of structural strength because of developing pack rust
• Money is no longer available for just cosmetic painting – to make the structure look good.
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Bridge Inspection criteria mainly evaluates only section loss (of steel) from corrosion,
but not the effects of crevice corrosion and
pack rust, even though it can cause:
• Bending beams and compression members
• Locking up components of moveable bridges
• Reduction in safety factors
• Reduction in seismic strength and ductility
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Could Crevice Corrosion & Pack Rust have Contributed to this?
Probably, yes
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INSPECTION FOR PACK RUST
• The new PONTIS computerized bridge evaluation program includes a “Smart Flag” for Pack Rust
• The PONTIS program was developed by and for the States (with FHWA funding) – and it is now being used by many States and some toll agencies.
• Now – structures can be ‘posted’ because of the effects of serious pack rust.
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PONTIS – Condition State 1
• The connection is showing signs of rusting between plates. Seams of the connection exhibit rust staining
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PONTIS – Condition State 2
• Rusting between plates is beginning to distress the connections. Minor swelling exists.
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PONTIS – Condition State 3
• Rusting between plates has caused serious distress to the connection. The plates may be badly distorted, however all connectors (rivets/bolts) are still functioning.
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PONTIS – Condition State 4
• Rusting between plates has caused serious distress to the connection, which warrants analysis of the bridge to ascertain the impact on the bridge. Some rivets or other connectors may have popped or are no longer effective.
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Regarding the Analysis
• The analysis of such bridges (with distorted members and weakened connections) should include an assessment of seriously reduced buckling strength, ductility, and seismic resistance.
• Strengthening for loads and seismic ductility may be required.
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Crevice Corrosion & Pack Rust
Explanation of the crevice corrosion & pack rust
phenomenon
The corrosive environment inside of crevices is much
more severe and destructive than surface corrosion
• Crevice corrosion is localized and is caused by crevice geometries.
• Stagnant solutions set up highly corrosive micro-environments inside such crevices.
• A metallic material tends to assume a more anodic condition in the stagnant crevice solution.
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Rust
Crevice corrosion and
Pack rust phenomena
• Crevice corrosion is usually the result of a differential oxygen concentration cell, in which the mouth of the crevice is richer in oxygen than the metal interface within the crevice, which becomes anodic and dissolves (corrodes).
• Subsequent pH shifts within the crevice can lead to even more intensified attack. The metal ions produced by the anodic corrosion reaction readily hydrolyze – giving off protons (acid) and form corrosion products
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Rust
Crevice corrosion and
Pack rust phenomena
• The pH in a crevice can reach very acidic values – sometimes equal to pure acids.
• The corrosion products seal and further accelerate corrosion in the crevice environment.
• The accumulation of positive charge in the crevice becomes a strong attractor to negative ions in the environment, such as chlorides, sulfates and nitrates – that can be corrosive in their own right.
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Rust
Crevice corrosion and
Pack rust phenomena
• The positively charged crevice – when sealed by a coating which is porous – draws moisture and contaminates through it.
• Thus, the above results will occur if the crevice is sealed with a coating or caulking without the use of an active penetrant to neutralize the active corrosion producing chemistry within the crevice.
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Rust
Crevice corrosion and
Pack rust phenomena
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Rust
Louisiana DOT bridge. One one night – they lost 29 rivets
Severe corrosion and pack rust problem – on a PA Turnpike bridge – chemically stopped
with Termarust
• 10 yrs ago this bridge was sandblasted & a 3-coat paint system was applied’ that didn’t even slow down the crevice corrosion, and the 3” thick pack rust in the connections of the main girders
• In April 2006 they had a contractor do 5,000 psi pressure wash cleaning and apply Termarust – JUST OVER THE CONNECTIONS
• This (zone painting) project carries a joint 5-yr warranty
• The crevice corrosion has been stopped
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Rust
Edge of steel angle in the
corner of the box member –
side plates are bent out 3” &
top plates bent up 3”
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Rust
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Rust
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Rust
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Rust
Cleaning is NOT done by sandblasting, because
• It cannot remove the active crevice corrosion, near the tip of the crevices
• Although it will remove some of the pack rust - it can also pack the crevices with sand
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Cleaning IS DONE with a 5,000 psi pressure washer, at a 4” standoff distance,
because
• It will blow out most of the (inert) pack rust
• It will flush the connection (and crevices) as clean as possible
• It is much less expensive and more environmentally ‘friendly’ than sandblasting
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Power Washing and Overcoating is Effective and Much Less Expensive than Sandblasting and Completely Repainting a
Bridge
Abrasive Blasted High Pressure Water Cleaned
Advantages of Abrasive Blasting and High Pressure Water Cleaning (HPWC)
Abrasive Blasting
• Removal Of Lead based paint
• Prepare surface for zinc based coating
• Cosmetics
HPWC
• Effectively cleans structure critical crevice corroded connections
• Cost effectively removes Non Visible contaminants
• Provides a stable substrate for over coating
• Potential for at least 50% project cost savings
1 yr old 3 coat zinc epoxy urethane over pack rust
Crevice corroded connections not washed before coating to
remove the active salts or chemically treated to neutralize
the active corrosion: Resulting chemistries were sealed and
created an oxygen concentration cell and failure
Crevice Corroded Connection Washed before Abrasive Blasting and Coating
• to remove the active salts
• chemically treated with HR CSA penetrant to neutralize the active corrosion causing chemistries
• sealed up with a top coat based on HR CSA* neutralization chemistry
• Coating failure has not occur in 12 years
*HR CSA (High Ratio Co-Polymerized Calcium
Sulfonate)
Crevice Corroded connections treated with
an HR CSA* corrosion control coating on
the High Level Bridge Edmonton, Alberta,
Canada after 12 years the crevice corrosion
has been stopped
Pack rust and Crevice corrosion can overstress
structural connections
This structure has coating failure in the joints and connections, caused by severe crevice corrosion and pack rust, but the coating on the flat surfaces is relatively intact
Power Washing and Overcoating is Effective and Much Less Expensive than Sandblasting and Completely
Repainting a Bridge
by
Wayne
Senick,
Technical
Director
and
Craig
Ballinger,
P.E.
Termarust
Technologies
Abrasive Blasted High Pressure Water Cleaned
Advantages of Abrasive Blasting and High Pressure Water Cleaning (HPWC)
Abrasive Blasting
• Removal Of Lead based paint
• Prepare surface for zinc based coating
• Cosmetics
HPWC
• Effectively cleans structure critical crevice corroded connections
• Cost effectively removes Non Visible contaminants
• Provides a stable substrate for over coating
• Potential for at least 50% project cost savings
1 yr old 3 coat zinc epoxy urethane over pack rust
These Crevice corroded connections were not washed
before coating to remove the active salts, not chemically
treated to neutralize the active corrosion causing chemistries
and were then sealed - which created an oxygen
concentration cell and failure occurred
Crevice Corroded Connection Washed before
Abrasive Blasting and Coating
• to remove the active salts
• chemically treated with HR CSA penetrant to neutralize the active corrosion causing chemistries
• sealed up with a top coat based on HR CSA* neutralization chemistry
• Coating failure has not occur in 12 years
*HR CSA (High Ratio Co-Polymerized Calcium
Sulfonate)
Crevice Corroded connections treated with
an HR CSA* corrosion control coating on
the High Level Bridge Edmonton, Alberta,
Canada after 12 years the crevice corrosion
has been stopped
Pack rust and Crevice corrosion can overstress
structural connections
This structure has coating failure in the joints and connections, caused by severe crevice corrosion and pack rust, but the coating on the flat surfaces is relatively intact
Cleaning IS DONE with a 5,000 psi pressure washer, at a 4” standoff distance,
because
• It will blow out most of the (inert) pack rust
• It will flush the connection (and crevices) as clean as possible
• It is much less expensive and more environmentally ‘friendly’ than sandblasting
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The next steps are to:
1. Blow the connections dry – with drycompressed air
2. Apply a liberal amount of the Termarust high ratio calcium sulfonate Penetrant into the crevices; i.e. connections
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The High Ratio, co-polymerized, Calcium Sulfonate Penetrant
• Has a pH of 10.5 (a chemical base)
• Has a polar attraction to steel
• Penetrates into the active corrosion layer, at the steel-pack rust interface; i.e. under the pack rust
• Neutralizes the acid
• Displaces moisture
• Absorbs oxygen
• Chemically stops active crevice corrosion4/26/2015 46
Crevice Corrosion & Pack Rust
Applying TR2200
Penetrant
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Rust
TR2200 Penetrant has
been liberally applied into
the connections
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Rust
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Rust
The ‘finishing’ steps are to apply, wet-on-wet:
1. A 10 mil DFT (18 mil WFT) caulk/stripe coat layer of the high ratio calcium sulfonate Topcoat over the Penetrant in/on the connection’, then
2. 5 mils DFT (9 mils WFT) of Topcoat, over areas of bare steel or contaminant free rust, and
3. An additional 5 mils DFT (9 mils WFT) over all areas to be painted
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For a quick demo to the Contractor and
the engineers, the TR2100 Topcoat was
applied by brush – when (usually) applied
with spray – the surface is very smooth
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Rust
The final thicknesses of the high ratio Calcium Sulfonate (HR CSA)Topcoat are:
1. 5 mils DFT over tightly adhered existing paint
2. 10 mils DFT over areas of bare steel or contaminate free rust
3. 20 mils DFT over connections – that had active crevice corrosion
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CONCLUSIONS
• Crevice corrosion and pack rust can be a serious structural problem.
• This problem can be CHEMICALLY stopped.
• This problem has been solved with an ACTIVE high ratio, co-polymerized, calcium sulfonate(HR CSA) coating system; that has a 19-year field proven history; i.e. 19 years and still no corrosion.
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Our Information
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Thanks!Ready for Discussion
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Rust
The Quebec Bridge Story
The Quebec Bridge Story(Background)
• In original Quebec bridge project, the bid documents required sandblasting & a 3-coat paint system (zinc, epoxy, urethane)
• The lowest bid price was extrapolated for the whole bridge – the estimated total cost was $250 Million ( without stopping the crevice corrosion)
• The same portion of the Quebec bridge was re-bid specifying Termarust. The low bid was only $110 Million.
• Total estimated cost savings = $140 Million = 56% cost savings.
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The Quebec Bridge Story(More Background)
• In at least 4 bridges work was done in the Winnipeg area – by 5,000 psi pressure washing & Termarust(formerly called Bridgecote)
• Not only was the crevice corrosion stopped – the projects were covered by a joint Contractor-Termarust 5-year warranty against coating system failure
• With no exclusions for crevices & crevice corrosion
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The Quebec Bridge Story(Successful Conclusion)
• Used 4 bridges experience in the Winnipeg area with 5,000 psi pressure washing & Termarust (formerly called Bridgecote) in rebidding process
• The same portion of the Quebec bridge was re-bid specifying Termarust. The low bid was only $110 Million.
• Total estimated cost savings = $140 Million = 56% cost savings
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Rust
Lancaster, PA Bridge Story
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Rust
Lancaster, PA Bridge Story
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Rust
Lancaster, PA Bridge Story
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Rust
Lancaster, PA Bridge Story
The Quebec Bridge Story(Background)
• In original Quebec bridge project, the bid documents required sandblasting & a 3-coat paint system (zinc, epoxy, urethane)
• The lowest bid price was extrapolated for the whole bridge – the estimated total cost was $250 Million ( without stopping the crevice corrosion)
• The same portion of the Quebec bridge was re-bid specifying Termarust. The low bid was only $110 Million.
• Total estimated cost savings = $140 Million = 56% cost savings.
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The Quebec Bridge Story(More Background)
• In at least 4 bridges work was done in the Winnipeg area – by 5,000 psi pressure washing & Termarust(formerly called Bridgecote)
• Not only was the crevice corrosion stopped – the projects were covered by a joint Contractor-Termarust 5-year warranty against coating system failure
• With no exclusions for crevices & crevice corrosion
4/26/2015 66Crevice Corrosion & Pack Rust
The Quebec Bridge Story(Successful Conclusion)
• Used 4 bridges experience in the Winnipeg area with 5,000 psi pressure washing & Termarust (formerly called Bridgecote) in rebidding process
• The same portion of the Quebec bridge was re-bid specifying Termarust. The low bid was only $110 Million.
• Total estimated cost savings = $140 Million = 56% cost savings
4/26/2015 67Crevice Corrosion & Pack Rust
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