Failure Analysis: Cracking at Reactor Exit Collector of Platforming Unit

 At December 2007 a leak was observed at second reactor R-4802 collector (2-1/4 Cr - 1 Mo), conveying the effluents to the 3rd furnace F-4803 of Semi-regenerating Platforming unit (Unit 048) of Petit Couronne Refinery – France.
Operational Conditions:

	Design	Operation
Temperature (°C)	543	500
Pressure (Bars)	37,8	28,6
Fluid :	Hydrocarbons (Naphtha + Hydrogen)
Collector Material	Low alloy steel type P22

Metallurgical examination shows that cracking was initiated by a localized mechanism known as Creep Type IV at HAZ fine grain zone.  Additional constraints produced by rest of refractory blocking also helped with the development of failure. At operational conditions creep type failures was not expected; but fine grain zone configuration aids to develop the cracking.
 Actions to avoid small grain size zone were implemented, as to use materials with control of the impurities, use of materials with addition of boron (90 to 130 ppm); welding procedure considering pre-heating at 200°C and interpass temperature up to 250°C and PWHT at 760°C during 1h /inch thickness.

Also Inspections actions were taking to assure the quality of repairs and recommendations were implemented in order to modify the design and avoid the blocking of furnace’s tubular elements.  Additionally on-site metallurgical examination was included as part of inspection plan.