Polythionic acid stress corrosion cracking
(PASCC) in stainless steel is a downtime phenomenon. For heaters with stainless
steel tubes, an evaluation should be made to determine their susceptibility to
internal and external PASCC. If deemed necessary, specific steps should be
taken to prevent cracking during downtime. These procedures are detailed in
NACE RP 0170. When using a soda ash wash solution to externally protect tubes,
care should be taken to protect any ceramic fiber insulation from becoming
wetted as the fiber can sag under the weight of the absorbed liquid.
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