caster spray chamber corrosion -...

Caster Spray Chamber Caster Spray Chamber Corrosion

ChemTreat’s Steel Industry Water Conference 9-12 to 9-14-2012 , Clearwater Beach FL* Confidential * Do Not Duplicate without Permission 1

Effects of Poor Corrosion Control

• Destruction of AssetsDestruction of Assets• Safety Concerns• Increased Maintenance Costs

ChemTreat’s Steel Industry Water Conference 9-12 to 9-14-2012 , Clearwater Beach FL* Confidential * Do Not Duplicate without Permission

• Lost Production2

Caster Spray Chamber Corrosion

• Causes– Mold Powders

– Steam Evacuation

Chlo ide Attack– Chloride Attack

• Effects

• Solutions• Solutions


Contact Cooling Water – Mold Powder

Acid corrosion produced in this zone by mold powder by-products dissolved p y p

in spray water and condensate.


Spray Chamber Corrosion

Mold Powders

Volatile fluorine compounds + H2O ---- SiF4

SiF4 + 2H20 ---- 4HF + SiO2

HF dissolves iron oxide at pH <4

C i D T HF Att kCorrosion Due To HF AttackCan Exceed 100 MPY



Frequent repairsFrequent repairsto beam due to

Acid Attack Acid Attack Coupon Results Underneath Foot Rolls



Deep metal ploss due to HF at end of rollroll


Spray Chamber Corrosion – Steam EvacuationEvacuation

Sprays coolingcoolingbillet. Overspray andsteam migrationmigration



Slab caster spray chamber

Steam Condensation Resulting in Pure, Aggressive Aggressive Water



Uneven, inconsistent inconsistent, intermittentwater exposure promotes atmosphericpoxygen corrosion

Corrosion Rates typically 20 30 MPY


20-30 MPY

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Spray Chamber Corrosion – Chlorides

•Oxygen corrosion aggravated by chlorides can corrode at a rate of 200MPY.

Chl id ib d b h l •Chlorides contributed by halogen can increase due to heavy organic fouling.



Mild corrosioni hi h i lwithin horizontal

zone after 4 yearsof caster operationof caster operation



Heavy oil and grease leaks led grease leaks led

to increased halogen demand g

increasing chloride levels


Corrosion Control

General corrosion rates should be maintained at less than 5 mpy to minimize the impact of spray chamber corrosion.

This however does not dictate a low corrosion rate in the spray chamber, only p y , yminimizes the potential.

* Profile the chamber with Corrosion coupons and online corrosion monitiors.


Caster Structure Corrosion Profile

TEST LOCATION SPECIMEN MAY JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY APRIL MAY JUNE JULY

LOCATION TYPE Peroxide Stabilized Bromine Bleach Bleach Bleach Bleach Bleach Bleach Bleach Bleach Bleach Bleach Bleach Bleach

caster lower north west of strand 4 mild steel 1.5 4.9 1.6 1.7 0.9 0.4 0.3 1.6 1.5 1.1 8.4 1.2 4

caster lower middle west of strand 2-3 mild steel 3.4 4.9 4.1 9.8 12.5 0.9 0.9 6.4 1.4

caster withdraw north west of strand 4 mild steel 3 1.4 7 13.3 3 3.2 4 0.3 11 1.1 1.1 14.1 18.2

caster withdraw middle west of strand 2-3 mild steel 1.8 2.8 4.2 7.7 6.9 1.3 4.3 0.5 0.3 4.3 22.1 34.8 70.2

Straightener Ceiling below withdraw motor (strand 4) mild steel 1.3 0.3 1.1 3.3 2.8 2.6 0.3 0.5 0.5 0.7 1.8 2.8

Straightener Ceiling below withdraw motor (strand 1) mild steel 1.1 0.2 1.4 0.4 0.2 0.9 0.3 0.4 31.8 0.8 0.4 1.1 2.7

Straightener Ceiling Beam North (inside east strand 4) mild steel 17.8 0.6 8.3 46.3 2.7 2.4 13.8 14.1 2.7 19.7 41.1 37.6 1.5

Straightener Ceiling Beam South (inside east strand 1) mild steel 10.6 29.7 22.9 49.8 24.4 38.6 47.9 0.4 27.7 34.6 45.7

Withdraw ceiling above motors (middle of strands) mild steel 1.6 0.4 2.1 1.7 1.6 0.7 0.1 0.2 0.7 1.2 0.5 2.8

Caster Spray Chamber North (east of strand 4) mild steel 59.2 43.5 50.5 49.7 49.1 72.5 41.8 48.6 37.6

Caster Spray Chamber Middle (east of strand 2) mild steel 58.9 64.9 82 82.5 64.6 69 60 53.8 31 7.2 21.2

Withdraw Ceiling West Beam (west strand 4) mild steel 8.6 0.5 2.8 1.9 2.2 1.3 0.2 1 2.7 3.3 1.9 1.4

Withdraw Ceiling West Beam (west strand 1) mild steel 3.3 0.8 1.6 1.4 3.2 1.9 5.9 4 26.1 11 47.6 0.7 2.5

Withdraw Ceiling Beam North Side mild steel 4 0.3 1 1 0.6 0.5 0.6 0.9 1.5 2.1 0.4 1.7

Withdraw Ceiling Beam South Side mild steel 1.7 27.4 38.4 2.4 2 1.5 1.6 2 23 24.9 1.1 0.8

Inside Spray Chamber Strand #2 mild steel 58.8 49.3 68.2 64.8 74.1 55.3 51.5 63.9 49.9 73.8 1.4

Spray Chamber Ceiling East of Doors (middle) mild steel 20.6 3.2 16.6 15.7 9 8.5 10.4 7.8 14.7 4.4 6.2 8.7 2.3

C C t d With P i P t ti ild t l 34 5Coupon Coated With Primer Protection mild steel 34.5

1. Structure Corroded Requiring Large Capital to Repair2. Water/Water Treatment Blamed for Corrosion3. Profile Determined Steam Evacuation Main Cause for Corrosion


4. Improved Monitoring/Awareness Resulted in Extended Structure Life

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Corrosion Control

• Improved Mold Powder Practices• Exhaust Fan Analysis/Evaluationy /• Corrosion Inhibitors• Alkalinity Supplements (for HF)

S t W h S (f HF)– Separate Wash Sprays (for HF)– Metal Shields/Material Change

• Vapor Phase Inhibitors• Improved Water Quality

– Chloride Reduction• Grease/Oil Reduction/• Halogen Reduction• Chlorine Dioxide and Hydrogen Peroxide substitution for Bleach.

• Organic & Inorganic Coatings


g g g• POR 15 (Paint Over Rust)

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Alkalinity Supplements

• Caustic (NaOH)• Sodium Bicarbonate (Liquid or Dry)• Sodium Bicarbonate (Liquid or Dry)• Soda Ash (Liquid of Dry)• Minimum Alkalinity varies….prefer 200 ppm

The key is to maintain enough alkalinity in the spray water being supplied to the upper zone to buffer/neutralize the

acids being generated.acids being generated.

•Another method is to install a secondary spray system to flush additional water into the area to neutralize the acids. Essentially adding more alkalinity to the area. •Caution must be made to not impact the cooling of the strand and affect product quality.


Testing for HF Production

Sp a ate sample Spray water sample collection from breakout platebreakout plate


Alkalinity Supplement / Materials

• Stainless steel grates and • Stainless steel grates and shields installed

• Alkalinity supplement • Alkalinity supplement added to spray water


Vapor Phase Inhibitors for Spray ChamberChamber

• Inhibitors must cover bare surfaces and/or top layers of rust or they will be ineffectivelayers of rust or they will be ineffective.

• Must be adequately supplied throughout spray chamber. Shielded zones may be difficult to

h reach. • May be significant loss of inhibitor through

ventilation system.y• Safety, odor• Potential nozzle pluggage if fed through spray

water line Separate feedline may be water line. Separate feedline may be considered.

• HF acid corrosion control?


Improved Water Quality

• Chloride Reduction– Oils and Greases must be removed on a regular

basis to minimize the halogen demand• Spills should not be accepted as the “norms” of • Spills should not be accepted as the norms of

operating

– Glycol leaks must be minimized!!!– Halogen residual control is very important at all

times ensuring good microbio control, but minimize halogen contributionminimize halogen contribution• Alternatives to Bleach – prefer max 250 ppm chlorides• Chlorine Dioxide and Hydrogen Peroxide


Coating Technologies

• Choice of Coating Material for Environment is Critical to Its Success

• Application is Just as Important to the pp pMaterial Choice

• Just as with the equipment in a mill, q p ,maintenance of the coatings is necessary to ensure desired results are obtained.



Replacement epoxy coating



Two years laterlater



Failed coatingsFailed coatings• Corrosion on carbon

steel components

Localized (Focused) Corrosion occurs at the coat fracture.


Takeaways – Caster Structure CorrosionCorrosion

•Casters are very dynamic systems with significant •Casters are very dynamic systems with significant stresses due to Mold Powder, Steam Evacuation, Chlorides

•Monitor and Profile Caster Structure Corrosion

•Improve Mold Powder Operations

•Ensure Proper Steam Evacuation

•Minimize Contaminants, i.e., Oils, Greases, Glycols

•Determine Best Method for Bio Control

•Maintain Proper Operating Water Parameters


p p g

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