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.
(gms@sabnis.com)

Crevice Corrosion & Pack
Rust
A Serious Structural
Problem
By
Craig 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 vs
pressure 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 Stopped
with
Active High Ratio, Co-Polymerized,
Calcium Sulfonate Coating System

Many old truss bridges
have 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.

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 18
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 products4/26/2015 19
Rust
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 20
Rust
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 21
Rust
Pack rust phenomena

4/26/2015 22
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

4/26/2015 24
Rust

Edge of steel angle in the
corner of the box member –
side plates are bent out 3” &
top plates bent up 3”
4/26/2015 25
Rust

4/26/2015 27
Rust

4/26/2015 28
Rust

4/26/2015 29
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

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

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

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 dry
compressed 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 corrosion

Applying TR2200
Penetrant
4/26/2015 47
Rust

TR2200 Penetrant has
been liberally applied into
the connections
4/26/2015 48
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4/26/2015 49
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

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
4/26/2015 51
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

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

4/26/2015 57
Rust
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.

(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

(Successful Conclusion)
• Used 4 bridges experience in the Winnipeg area with
5,000 psi pressure washing & Termarust (formerly
called Bridgecote) in rebidding process
specifying Termarust. The low bid was only $110
Million.
• Total estimated cost savings = $140 Million = 56%
cost savings

4/26/2015 61
Rust
Lancaster, PA Bridge Story

4/26/2015 62
Rust

4/26/2015 63
Rust

4/26/2015 64
Rust

(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)
specifying Termarust. The low bid was only $110 Million.
• Total estimated cost savings = $140 Million = 56% cost
savings.

(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

(Successful Conclusion)
• Used 4 bridges experience in the Winnipeg area with
5,000 psi pressure washing & Termarust (formerly
called Bridgecote) in rebidding process
specifying Termarust. The low bid was only $110
Million.
• Total estimated cost savings = $140 Million = 56%
cost savings

Delhi sabnis corrosion termarust on crevice corrosion (1)

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