Corrosion Under InsulationPart I

SABIC Saudi CUI Forum

By

Dik BetzigHi-Temp Coatings Technology Co.

bz@hitempcoatings.comP +01 978 635 1110C +01 978 844 0238F +01 978 635 1124

BiographyDik Betzig

• BS ChE University of Massachusetts• MSE UMass Lowell, Nypro Institute of Polymer Chemistry

• 1978-1982 Engineered Polymer Systems, Clinton, MA• Product Development Manager• Engineered plastic compounding and extrusion. Specializing in crystal and

amorphous heat & chemical resistant resins, SBS, Nylon 66, polycarbonates Kynor,

• 1982-1995 Case International, Chicago• VP General Manager/Pomco, Port Manatee, FL• Specialty concrete infrastructure: Slurry walls, Precast & post mentioned

concrete structures, Bridges, Stadiums and correctional facilities.• 1995-2006: Dampney Company Inc., Boston MA• VP of Product Development & Research• Manufacturer of specialty high temperature liquid coatings for IM & OEM • 2006-Present: Hi-Temp Coating Technology, Acton, MA• VP Technical Sales and R&D• Developer and manufacturer of hi temperature coatings for Industrial

applications.• Specializing in petrochemical, power generation and specialty OEM.

Understanding & specifying solutions to

corrosion under insulation

Introduction• In many process plants it is normal procedure to insulate

areas operating above 60°C (140°F), which are accessible to operators and presents a safety risk for burns and skin damage. At higher operating conditions it is necessary to insulate in order to prevent heat losses and improve the efficiency of the process.

• Typically, insulation used has been based on Rockwool, Foam Glass or Calcium Silicate. These materials have different degrees of water uptake but all require cladding to seal from the weather and prevent water penetrating cracks and joints’ and reaching the steel surface.

The Problem

• CUI can cause catastrophic accidents.• Shell Norco Refinery blew up as a direct result of

corrosion under insulation• Vast property damage and contamination• Shell bought the entire town of Good Hope, LA.• Cost of ethylene glycol antifreeze went up by 25%

Shell Narco Plant, TX

Mechanism of CUI• Availability of oxygen

As temperature increases, the amount of oxygen dissolved in solution decreases as the boiling point is reached, resulting inreduced corrosion rates. However, on a surface covered by insulation a poultice effect is created which holds the moisture by capillary action.

• High temperatureFor high temperature equipment water entering an insulation

material and defusing inward will eventually reach a region of dry-out at the hot pipe or equipment wall. Next to the dry-out region a zone adjacent to the pores of the insulation are filled with saturated salt solution. When a thermal process change occurs salt solution moves into the metal wall.

• Concentration of dissolved speciesWhen precipitation becomes trapped by insulation, corrosive

chlorides and acidic sulfides concentrate and accelerate corrosion. The drying/wetting cycles in CUI associated problems are a strong accelerator of corrosion damage. Formation of aggressive chemistry can lead to the worst corrosion problems including stress, corrosion, cracking, and premature equipment failure.

Reasons for CUI Problem

• Corrosion is hidden• Inspection is limited, costly & difficult• Equipment runs at variable state• No Insulation is 100% waterproof• Wet insulation = high corrosion• Costly shut-down for equipment• There is never enough budget

Inspection of CUI

• Visual procedure is to cut plugs in the insulation that can be removed and allow for ultrasonic testing. Corrosion tends to be localized and this process is ineffective.

• Eddy current techniques• X-ray and TV monitoring• Electromagnetic devices

Prevention of CUI

• Careful selection of insulation materials• Use of protective coatings with dual

Corrosion control mechanism.• Special coating systems with proven

performance

Coating Choices for CUI

• Novolac epoxies and vinylesters• Inorganic zinc• Epoxy modified silicone• Modified silicones• Silicone aluminum• IPN silicones [interpenetrating network]• Inorganic hybrids [silicone/ceramic]• TSA - Thermal spray aluminum

Novolac Epoxies & Vinylesters• Operating temperatures 20°C ~ 180°C• Life claimed (varies with temperature)• Mechanism is inhibitive/barrier• Good abrasion resistance• Good chemical resistance• Steady-state environment• Poor thermal cycling• Film thickness 6-10 mils (150-250 microns)• Two-component

Novolac Expoxies

• Developed from Novolac hot-product tank lining epoxies.

• Have all the advantages and disadvantages of ancestor tank linings.– Maximum operating temperature ~ 180 °C– Film embrittlment at this temperature, fails above it.– Two-component, relatively low solids materials, short

pot life.– Surface preparation of SSPC SP 10 is mandatory– Recoat Intervals (minimum and maximum) are critical– Exact film thickness is critical – Thick films fail very quickly

Novolac Epoxies• Maximum Operating Temperature: 400° F./204 °C.• Maximum DFT per Coat: 4 mils/100μ• Recoatable with self for CUI ? Yes • Maximum Total DFT for CUI Service: 8 mils/200μ• Surface Prep Required for CUI: SSPC SP 10• Single Component, No Catalyst NO (Complex Application)*• Usable on Stainless Steel to prevent stress cracking? Yes**• Tie-in and Field Repair/Recoat with Self? Yes • Corrosion Resistant at Ambient Temperatures? Yes • Survives Intermittent Immersion in Hot Salt Water? Yes • Anodic/ metal content sacrifices in Electrolyte? No• Apply to hot surfaces? Maximum Temperature: Yes(300°F/150 °C.• Suitable for Cyclic Cryogenic Service? No

*Maximum Dry Film Thickness and Recoat Intervals are Critical**Maximum Operating Temperature is very low for SS units.

Inorganic Zinc

• Operating temperatures 20°C ~ 400°C• Life claimed (varies with temperature)• Mechanism is anodic sacrificial• Good abrasion resistance• Film thickness 3 mils (75 microns)• Two-component• Good thermal cycling

Inorganic Zinc Coating (IOZ)• Inorganic Zinc has been a staple of CUI systems for

decades– In the 1970’s and 1980’s IOZ over-coated with Thin Film Silicone

was a CUI standard

• Inorganic Zinc is an ANODIC Sacrificial Coating system– In CUI service, IOZ sacrifices wherever moisture reaches the

steel– Polarity reversal in sodium chloride at 70/80°C becomes anodic

and protects the zinc which is slightly acidic or alkaline– The zinc is more soluble in warm water present and any move

from neutral ph will cause an increase in solubility

• Several major refinery accidents have been traced to perforation of IOZ- coated insulated (CUI) equipment.

Inorganic Zinc Coatings (CUI)

• Maximum Operating Temperature: 750° F./400 °C.• Maximum DFT per Coat: 3 mils/75μ• Recoatable with self for CUI ? NO• Maximum Total DFT for CUI Service: 3 mils/75μ• Surface Prep Required for CUI: SSPC SP 6• Single Component, No Catalyst NO• Usable on Stainless Steel? NO• Tie-in and Field Repair/Recoat with Self? NO• Corrosion Resistant at Ambient Temperatures? Yes• Survives Intermittent Immersion in Hot Salt Water? FAILS• Anodic/ metal content sacrifices in Electrolyte? YES• Apply to hot surfaces? Maximum Temperature: NO• Suitable for Cyclic Cryogenic Service? NO

Results from Inorganic Zinc

Epoxy Modified Silicone• Operating temperatures 20°C ~ 180°C• Life claimed 3-10 years• Mechanism is inhibitive• Good abrasion resistance• Corrosion inhibitive mechanism• Steady-state environment• Poor thermal cycling• Moderate chemical resistance• Film thickness 10-12 mils (200-250 microns)• Two-component

Modified Silicones

• Operating temperatures 20°C ~ 250°C• Life claimed 3-10 years• Mechanism is inhibitive• Thermo plastic• Fair abrasion resistance• Film thickness 4-5 mils (100-125 microns)• Single-component

Silicone Aluminum

• Operating temperatures 20°C ~ 650°C• Modest abrasion resistance• Mechanism is barrier protection• Life claimed (varies with temperature)• Single-component• Good thermal cycling• Dry-heat environment• Film thickness 2-4 mils (50-100 microns)

Thin Film Silicones• Thin film Silicone Coatings survive temperatures to 1000° F./538 °C.• Have minimal film build, typically 1.5 mil/37μ per coat maximum• Number of coats is restricted to two or three at most.

• These coatings work well on exposed hot surfaces but fail in CUI.• The thin film has no resistance to immersion or steam interface.• The thin film has no corrosion resistance at ambient temperatures.

• These coating systems were superseded by polysiloxane, which has higher DFT, but fails rapidly in cyclic service.

Thin Film Silicone Coating• Maximum Operating Temperature: 1000° F./538 °C.• Maximum DFT per Coat: 1.5 mils/37μ• Recoatable with self for CUI ? Yes• Maximum Total DFT for CUI Service: 4.5 mils/113μ• Surface Prep Required for CUI: SSPC SP 6• Single Component, No Catalyst Yes• Usable on Stainless Steel to prevent stress cracking? NO• Tie-in and Field Repair/Recoat with Self? Yes• Corrosion Resistant at Ambient Temperatures? NO• Survives Intermittent Immersion in Hot Salt Water? FAILS• Anodic/ metal content sacrifices in Electrolyte? YES (Aluminum)• Apply to hot surfaces? Maximum Temperature: Yes (200°F.93 °C.)• Suitable for Cyclic Cryogenic Service? NO

IPN Silicones

• Operating temperatures 20°C ~ 200°C• Life claimed 3-10 years• Mechanism is inhibitive/barrier• Modest abrasion resistance• Multi-component• Film thickness 10-12 mils (250-300

microns)

IPN Silicone• This new class of products have been included in the new NACE RP for

offshore structures maintenance.

• They combine new resin technology and higher build characteristics than thin-film silicones and do not exhibit the micro cracking failure on cyclic service of polysiloxanes.

• Characteristics of these products vary considerably, Specialty Coatings Technologies are listed separately.

IPN Silicone• Maximum Operating Temperature: 800° F./427 °C.• Maximum DFT per Coat: 6 mils/150μ• Recoatable with self for CUI ? Yes • Maximum Total DFT for CUI Service: 8 mils/200μ• Surface Prep Required for CUI: SSPC SP 6• Single Component, No Catalyst NO• Usable on Stainless Steel to prevent stress cracking? Yes*• Tie-in and Field Repair/Recoat with Self? Yes • Corrosion Resistant at Ambient Temperatures? Yes • Survives Intermittent Immersion in Hot Salt Water? Not Recommended• Anodic/ metal content sacrifices in Electrolyte? YES (Aluminum)• Apply to hot surfaces? Maximum Temperature: Yes(250° F.120 °C.• Suitable for Cyclic Cryogenic Service? Yes

*Aluminum content may affect Stainless Steel

Inorganic Hybrids

• Operating temperatures 20°C ~ 600°C• Life claimed [varies with temperature]• Mechanism is anodic barrier• Good abrasion resistance• Film thickness 4-6 mils (100-150 microns)• Good thermal cycling• Multi-component

TSA - Thermal Spray Aluminum

• Operating temperatures -100°C ~ 500°C• Life claimed 25 - 30 years with minimal

maintenance• Mechanism is anodic sacrificial• Excellent abrasion resistance• Film thickness 8-10 mils (200-250

microns)• Sealant required for best performance

TSA Thermal Spray Aluminum

• Thermal Spray Aluminum has a good track record on exposed surfaces such as sheet piling, docks and buoys.

• Some specifiers recommend TSA for CUI service – this is a mistake

• TSA is an Anodic, Sacrificial Coating system• Once the TSA is sacrificed, electrolytic corrosion

accelerates.• Should be over-coated with inert films• Cannot be easily repaired• Recent testing (NACE 2006) shows TSA in hot salt water

immersion fails quickly

Thermal Spray Aluminum (TSA)• Maximum Operating Temperature: 1170°F/610°C.• Maximum DFT per Coat: 8 mils/200μ• Rec-oatable with self for CUI NO• Maximum Total DFT for CUI Service: 8-12 mils/200μ• Surface Prep Required for CUI: SSPC SP 10• Single Component, complex application Yes • Usable on Stainless Steel to prevent stress cracking NO• Tie-in and Field Repair/Recoat with Self? NO• Corrosion Resistant at Ambient Temperatures Yes • Survives Intermittent Immersion in Hot Salt Water FAILS• Anodic/ metal content sacrifices in Electrolyte YES • Suitable for Cyclic Cryogenic Service? Yes

Coating Criteria for New Construction• Incoming steel is abrasive blasted and zinc

coated• Service temperature is determined after zinc

coating• Must provide zinc-compatible hi-temp

systems• Air-dry, storable, transportable topcoats and

systems• Minimal damage to coatings during

installation• Quick and easy field touchup of welds and

damage• Compatible with specified insulation

Generic Products– High Solids Epoxy Novolac

Service temperature to 180CFilm thickness 4 mils (100 microns)

– High Build Ethyl SilicateService temperature to 500CFilm thickness 5 mils (125 microns)

– Silicone AluminumService temperature to 600CFilm thickness 2 mils (50 microns)

– Polysiloxane/SiliconeService temperature to 500 CFilm thickness 406 mils (100-150 microns)

Future Products

Next generation coatings:– Single-coat system– Suitable for use cryogenic to 500°C– Wet & dry cyclic performance– Suitable over wet blasting– Can be used for M&R or new construction– Surface tolerant– Dual mechanism barrier & inhibitive– Chemical resistant

Deficiencies associated with current CUI coatings

• Thin film resulting in pinpoint rusting / corrosion• Lack of coatings that can be applied while the

unit is online & hot• Thermal shock capabilities• The need for surface preparation• Wet & Dry thermal cycles• Heat cure issues• Short recoat windows

FairNONONOExcellentFairHigh-build Properties

GoodPoorPoorExcellentFairGoodAbrasion

Barrier/ Inhibitive

Anodic Sacrificial

InhibitiveAnodic Sacrificial

BarrierInhibitiveMechanism

7-15Varies3-1020-257-153-10Life claimed (yrs)

GoodPoorPoorGoodExcellentPoorWet & Dry

1 Coat

3 mils2No

3 Mils

400 C

Inorganic Zinc

NoYesN/ANoYesInterval Critical

6 mils1.5 mils8 mils6 mils4 milsDFT per coatmulti1N/A12ComponentsYesNoNoYesNoRe-coatable

8Mils4 Mils8 Mils30 Mils12 MilsMaximum DFT

500 C500 C600 C Peaks

600 C Cont.

200 CMaximum Temp.

New IPN Technology

Traditional Silicones

TSA Aluminum

HTC-1027 Primer

NovolacEpoxies

Comparison of Current CUI Systems

Under Corrosion Insulation Part II

A Systems Approach

Solving CUI

Clearly then, for most circumstances, corrosion under insulation can be prevented in two ways:

• By using a coating system which will prevent corrosion in the potentially hot, wet conditions existing under the insulation.

• Design insulation which will not be easily damaged and will prevent water ingress either by nature of the insulation or by an alternative more effective method of cladding.

Standard Testing for [CUI] Coatings

• ASTM B-117 SALT FOG– Scribed panel– 2500 hours minimum SALT FOG TEST– No under-creep

– UV RESISTANCE– INTERMITTENT IMMERSION– Hot Water Intermittent Immersion Tests

– ASTM 2485– Dry thermal cycling test [200oC to failure]

Performance Criteria for (CUI) Carbon Steel

– Resistance to Boiling Water [steam interface] – Heat and Thermal Shock Resistance – Direct Application to Hot Steel (up to 500° F./260°C.) – Application to Ambient Steel (new construction) – High Film Build Capability while Applying Directly to Hot

Steel – Application to a less than perfect surface preparation– Prevention of chloride induced stress corrosion cracking – Ideal for cyclic Service, including Cryogenic Temperatures– Simple to Use – Meets tightest current VOC and Environmental regulations

Performance Criteria for Stainless

• Provides protection for insulated austenitic stainless steels against chloride induced external stress corrosion cracking

• Contains a minimum of chloride, sulfides, and halides

• Thickness provides good barrier protection

Independent Testing Protocol by one of the world’s largest

oil & chemical companies to prevent corrosion under insulation for

application in their global under insulationprogram

Testing Procedure

1) In dry oven at 208°C for 16 hours - heat resistance.

2) Quenched into cold water - thermal shock resistance.

3) 99°C water for 8 hours.4) Repeat steps Monday through Friday5) In oven at 208°C for 2-1/2 days6) Quench panel into cold water…..

Repeat Test For An Additional 15 Weeks

Panels are periodically checked for cracking, fracturing, de-lamination, pinholes, corrosion, micro-cracking, softening, blistering, etc.

Summery of Test

• 2240 hours cycling• Thermal quenches 80• Immersion in 99ºC water 640 hours• Coating survived for 16 weeks

Summary CUI

1. Chemical Plant Equipment– CUI is more accelerated than common

atmospheric corrosion2. The corrosion rate in the drying and

wetting cycles is at the maximum immediately before drying

3. Corrosion during thermal cycling is 10-20 times greater than immersion service

Conclusion

Designers should select a CUI system which best combines:– Current cost effectiveness– Ease of application and insulation– Tolerance for expected future increases in

operating temperatures– Unexpected excursions from normal– Ability to repair after service life without

requiring complete removal of the original protective system

Questions ???