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. 03033 Corrosion 2003)

Introduction Covers period between 1950’s - 2003 Based on personal experience Joined a major Oil Company in 1954 - 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’. 14/01/04

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 14/01/04

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 14/01/04

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 14/01/04

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 14/01/04

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 14/01/04

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 14/01/04

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 14/01/04

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 - 1960’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 14/01/04

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) 14/01/04

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) 14/01/04

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 14/01/04