Delhi sabnis corrosion termarust on crevice corrosion (1)

Crevice Corrosion & Pack Rust: A Serious Structural Problem

By

Gajanan M. Sabnis, PhD, P.E.

Emeritus Professor, Howard University, Washington, DC.

([email protected])

mailto:[email protected]

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

4/26/2015 3Crevice Corrosion & Pack Rust

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


What is Crevice Corrosion and what is Pack Rust?

Why are they important?


Crevice Corrosion Can be Stoppedwith

Active High Ratio, Co-Polymerized,Calcium Sulfonate Coating System


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.


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


Could Crevice Corrosion & Pack Rust have Contributed to this?

Probably, yes


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.


PONTIS – Condition State 1

• The connection is showing signs of rusting between plates. Seams of the connection exhibit rust staining



• Rusting between plates is beginning to distress the connections. Minor swelling exists.



• Rusting between plates has caused serious distress to the connection. The plates may be badly distorted, however all connectors (rivets/bolts) are still functioning.



• 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.


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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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.

4/26/2015 18Crevice Corrosion & Pack

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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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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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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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Pack rust phenomena


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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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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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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


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


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


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


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


Applying TR2200

Penetrant


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TR2200 Penetrant has

been liberally applied into

the connections


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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


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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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


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.


Our Information



Thanks!Ready for Discussion



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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.


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


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


• Total estimated cost savings = $140 Million = 56% cost savings



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Lancaster, PA Bridge Story


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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)


• Total estimated cost savings = $140 Million = 56% cost savings.


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


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


• Total estimated cost savings = $140 Million = 56% cost savings


Technology

Delhi sabnis corrosion termarust on crevice corrosion (1)