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)

    mailto:gms@sabnis.com
  • Crevice Corrosion & Pack Rust

    A Serious Structural Problem

    ByCraig A. Ballinger,

    P.E. Termarust

    Technologies

  • Todays 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

  • Todays 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?

    4/26/2015 5Crevice Corrosion & Pack Rust

  • Crevice Corrosion Can be Stoppedwith

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

    4/26/2015 6Crevice Corrosion & Pack Rust

  • 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.

    4/26/2015 7Crevice Corrosion & Pack Rust

  • 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

    4/26/2015 11Crevice Corrosion & Pack Rust

  • PONTIS Condition State 2

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

    4/26/2015 12Crevice Corrosion & Pack Rust

  • 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.

    4/26/2015 13Crevice Corrosion & Pack Rust

  • 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.

    4/26/2015 14Crevice Corrosion & Pack Rust

  • 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.

    4/26/2015 15Crevice Corrosion & Pack Rust

  • 4/26/2015 16

    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.

    4/26/2015 20Crevice Corrosion & Pack

    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.

    4/26/2015 21Crevice Corrosion & Pack

    Rust

    Crevice corrosion and

    Pack rust phenomena

  • 4/26/2015 22Crevice Corrosion & Pack

    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 didnt 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

    4/26/2015 23Crevice Corrosion & Pack Rust

  • 4/26/2015 24Crevice Corrosion & Pack

    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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  • 4/26/2015 27Crevice Corrosion & Pack

    Rust

  • 4/26/2015 28Crevice Corrosion & Pack

    Rust

  • 4/26/2015 29Crevice Corrosion & Pack

    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

    4/26/2015 30Crevice Corrosion & Pack Rust

  • 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

    4/26/2015 31Crevice Corrosion & Pack Rust

  • 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 crev

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