Hardness Testing Offers Better Condition Assessment for Older Fired Heater Coils
According to Inspectioneering Journal, a methodology using hardness testing as the primary diagnostic tool can help engineers assess the condition of fired heater tube coils, particularly in older units built before the 1986 release of API 560. Writing in the March/April 2026 issue, Mechanical Integrity Engineer El Hazel Aymen explains that hardness readings can estimate remaining tensile strength using a correlation documented in API 579 Annex 2E, which can then be used to back-calculate the temperatures the tubes were likely exposed to.
What It Means for Subcontractors
- Inspection crews working on pre-1986 fired heaters should treat hardness testing as a core diagnostic step, not a secondary check, especially where tube skin thermocouple records are missing or unreliable.
- The API 579 Annex 2E correlation applies to carbon and alloy steels and austenitic stainless steels, but not to cold-worked materials, high-alloy steels, or nickel-based alloys, so crews need to confirm material type before applying this method.
- Pairing hardness readings with metallographic replication can help confirm whether microstructural degradation or creep damage has occurred, strengthening fitness-for-service evaluations.
