1. Corrosion Under Insulation A Historical Perspective
J.F.Delahunt
Carmagen Engineering Inc.
Presented by
S.Winnik
ExxonMobil Chemical
Based on a paper previously presented at NACE 2003 (Paper No Corrosion 2003)

2. Introduction Covers period between 1950’s - 2003
Based on personal experience
Joined a major Oil Company in Materials development Laboratory (Corrosion prevention and control)
No undergraduate courses on Corrosion available at that time
Completed post graduate course on Corrosion based on Uhlig’s 1948 textbook ‘Corrosion Handbook’. CUI not mentioned in this or in Uhlig’s 1965 edition entitled ‘Corrosion and Corrosion Control’.
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3. What CUI?
Original paper covered both CUI and CUF (corrosion under fireproofing). CUF not covered here.
From the mid 1950’s until the early 1970’s there was little CUI of carbon steel (cs)
Why?
Insulation only required if operating temperature was > 149ºC
However, external SCC of austenitic stainless steels (ss) was a concern in the mid 1950’s which resulted in extensive R&D to try and mitigate
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4. Insulation Types Typically used combination of
calcium silicate
mineral wool
asbestos
cork
cellular glass
Low cost of energy resulted in minimum temperature of > 149ºC before insulation applied
Insulation was required for ‘Cold’ services and for personnel protection if > 93 ºC
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5. Coating Protection Painting standards at that time were limited
Painting of insulated carbon steel vessels was only required if < 93 ºC
Insulated carbon steel piping not painted unless diameter > 750 mm
The ‘normal system consisted of hand/power tool cleaning plus two coats of air cured phenolic zinc chromate inhibited primer (maximum 75µm)
‘Severe’ systems added commercial grit blasting
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6. What Happened ? Events in the early 1970’s led to major changes
Oil crisis caused the cost of energy to soar - led to increased use of insulation systems at lower operating temperatures
New insulation systems introduced (such as organic insulating foams)
New processes came on-stream with lower and often cyclic operating temperatures
Insulation was applied to underground piping systems
Re-circulating salt water cooling systems employed
Use of austenitic stainless steels started to increase
Existing detailed engineering standards diluted
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7. CUI due to FIPP
Foamed in Place Polyurethane (FIPP) introduced into Europe
Marketed as a ‘closed cell impermeable insulating material’
Applied directly to uncoated steel with no topcoat with no concern regarding possible corrosion of carbon steel - FIPP believed to be immune to atmospheric weathering and UV exposure
Problems found with FIPP, massive failure resulted after only three years in service
Other problems found on primer coated carbon steel
Large moisture blisters developed on the steel surface during application
FIPP exothermic reaction caused ‘blowing and cell formation due to formation of reaction products with water when used as blowing agent
This led to foam cracking and subsequent degradation of the primer
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8. CUI Widespread
WW surveys indicated CUI occurred beneath all types of insulation
Insulation standards improved and required coatings to be applied for equipment operating
Typically between -1ºC to 93 ºC
Commonly between 4ºC to 82 ºC
CUI problems continued so range extended to
Initially -4ºC to 120 ºC
By the early 1990’s to -4ºC to 148 ºC
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9. CUI Mitigation Steps These included
Use of coatings for equipment in intermittent service
Coatings specified using the lower lowest design temperature
Vessel vacuum support insulated so as not protrude through the insulation
Insulation on tankage terminated 30-45cm above ground level
Coatings changed from two coats of maintenance primer to a single coat of epoxy primer to a single coat of high build epoxy phenolic
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10. Other Failures
Uncoated FIPP coating underground piping protected by CP
Caused by disbonded insulation shielded protective potentials
External Stress Corrosion Cracking become more prevalent
Mid 1950’s ’s ESCC experience in chemical plants and submarines
Led to development of calcium silicate insulation (inhibited)
Chemical plants started to specify protective coatings
Refineries had less of a problem
1970’s
Saw introduction of more inhibited insulation materials and greater use of epoxy and epoxy phenolic coatings
Cellular glass became preferred material
CP using Aluminium foil developed by ICI
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11. So ...Where Are We? Key developments include
Work by A.W.Dana in 1957 concerning prediction of ESCC
Knolls Atomic Power Laboratory investigation in 1965 leading into of ESCC by sodium silicate
W.G.Ashbaugh paper on ESCC also in 1965
J.F.Delahunt overview of CUI during NACE in 1980
ASTM Symposium ‘Corrosion of metals under thermal insulation’ in 1983
NACE symposium in 1989 ‘Corrosion under wet insulation’
NACE Recommended Practice RP 0198 in 1998
Introduction of novel inspection/NDE techniques and use of Risk Based Inspection (RBI)
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12. Lessons Learnt Some observations include
Reduction in capital costs still being sought by reduction in engineering standards
Insulated austenitic ss not coated to reduce costs
Low temperature carbon steel insulated with inadequate vapour barrier
Surprise still being expressed when ESCC of austenitic ss occurs
Paper published which indicated that corrosion on FIPP insulation cs was less severe than corrosion of exposed cs
Vessels still fabricated, coated, insulated and then transported from the fabrication shop to the construction site
Cost remains a major consideration
Where are we? CUI will continue for some time (although, hopefully to a lesser degree)
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13. Fireproofing
Concrete/ Gunnite systems extensively used for structural steel fireproofing
5 cm for structural steel
4 cm for vessels
Used fresh make up water free from impurities and a commercial grit blast for surface preparation
Steel work was not coated prior to fireproofing
For ‘severe’ services fireproofing ‘waterproofed’ by application of a bituminous coating (80 µm) plus a sealer
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