The electro-slag cladding process: application, main metallurgical and testing issues in the fabrication of reactors in large thickness 2¼Cr–1Mo–¼V

Abstract

In the fabrication of reactors (made of Cr–Mo steel modified with vanadium) operating in high hydrogen pressure and high-temperature service, internal cladding in austenitic stainless steel (typically made of AISI 347) is required in order to guarantee satisfactory corrosion resistance against the process fluids desulphurized hydrocarbons. Application of an electro-slag strip cladding (ESSC) process for internal weld overlay and clad restoring on heads, barrels and nozzles of 2¼Cr–1Mo–¼V reactors (with single-layer or double-layer technique) is described in the paper. The first part of the paper is focused on metallurgical aspects, cracking phenomena (hydrogen cracking, solidification cracking, under-clad cracking and hydrogen-induced disbonding) and cladding residual stresses referable to ESSC process. The second part of the paper is focused on operating aspects of the ESSC process and UT examination of weld overlay and clad restoring, optimized for the detection of planar defects under cladding.

Keywords::

• austenitic stainless steels
• chemical engineering
• cladding
• creep resisting materials
• disbonding
• electro-slag surfacing
• elevated temperature strength
• high temperature
• hydrogen embrittlement
• low-alloy Cr–Mo steels
• microstructure
• non-destructive testing
• plants
• post-weld heat treatment
• pressure vessels
• reheat cracking
• residual stresses
• service conditions
• solidification cracking
• stainless steels
• strip electrodes
• ultrasonic testing
• under-clad cracking

Notes

Paper presented at the ‘Giornate Nazionali di Saldatura 6’ [National Welding Days] during the workshop ‘Fabrication of structures and welded components’ – Genoa 26–27 May 2011.

Additional information

Notes on contributors

M. Mandina

Marcello Mandina was awarded a degree in Mechanical Engineering in 1994 at the University of Genoa. He has been an official of the Italian Institute of Welding since 1995. He is currently the manager of the Boilers and Pressure Vessels Department and Technical Assistance for Equipment and Systems under Pressure of the IIS Service. He carries out inspections and provides technical assistance in the field of welded structures, with particular reference to fabrication, testing and the repair of pressure systems and equipment.

M. Magnasco

Marco Magnasco was awarded a degree in Mechanical Engineering in 2002 at the University of Genoa. During the period 2003–2006, he worked for Lincoln Electric in Genoa as a technical manager for filler/overlay materials for welding. Since 2007, he has been employed by GE Oil & Gas Nuovo Pignone – Massa, where, until 2009, he was assigned the role of welding engineer in the reactor fabrication cell. As technical manager, since 2010 he has been supervising the welding engineering group for the GE Oil & Gas Turbo-Machinery Division, including various products, mainly reactors, exchangers, compressors and turbines.

G. Zappavigna

Giuseppe Zappavigna was awarded a degree in Physics in 1991 at the University of Genoa. From 1993 to 1998, he worked for the CMC at Genoa as Qualified Expert and Quality-Assurance Manager at important construction sites both in Italy and abroad. Since 1998, he has been employed by of GE Oil & Gas Nuovo Pignone – Massa, where he is Quality-Control Manager for activities relating to boilers at the plant itself and at the premises of main suppliers. He has currently attained the level-III qualification as regards UT, RT, MT, PT and VT methods and is NDE manager for the entire GE Oil & Gas Group.