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.