Construction of India’s 500 MWe Prototype Fast Breeder Reactor (PFBR) is in an advanced stage of completion. Prior to the start of construction, extensive research-backed technology development was planned and implemented for materials, welding consumables, fabrication of stringent-specification components and finalisation of inspection and testing procedures of fabricated components. With close interaction amongst design, materials engineers, materials and welding consumable manufactures, and fabrication industries, it has been possible to overcome the challenges during fabrication of all the structural welds. Valuable experience gained from these technology developments were inputs to design engineers in finalizing the specification of material, freezing the design drawing and charting out the quality assurance plan for each components. The synergy between designers, welding and inspection engineers and fabricators has contributed significantly to the progress with respect to construction of PFBR. Right from the preliminary design of the PFBR, IGCAR had realized the importance of welding both during fabrication and in service. Hence, a systematic programme was undertaken to integrate welding and fabrication and inspection aspects in design and selection of materials. This approach has enabled us to overcome the challenges faced during fabrication of the components with stringent specifications. A few examples of manufacturing technologies completed in time, and exceeding the specifications in most of the cases have been presented.

Placid Rodriguez Memorial Lecture - 2010
Delivered by
Dr V Balasubramanian
Professor & Director,
Centre for Materials Joining & Research (CEMAJOR),
Department of Manufacturing Engineering,
ANNAMALAI UNIVERSITY,
Annamalai Nagar – 608 002

"Friction Stir Welding: An Environmentally Cleaner Welding Process"

The respiratory effects often seen in full time welders include bronchitis, airway irritation, lung function changes, lung fibrosis, and a possible increase in the incidence of lung cancer. Traditionally, control of fumes and gases has been by enclosure and local exhaust ventilation, respiratory protective equipment may also be necessary in certain circumstances, in particular in confined spaces. In this context, an environmentally cleaner process has been invented at The Welding Institute (TWI), UK, which is popularly known as Friction Stir Welding (FSW) process. This comparatively recent innovation has permitted friction technology to be used to produce continuous welded seams for plate fabrication. Compared to many of the fusion welding processes that are routinely used for joining structural alloys, FSW is an emerging solid state joining process in which the material that is being welded does not melt and recast.  FSW is an environmentally cleaner process, due to the absence of a need for the various gases that normally accompany fusion welding. FSW process produces no smoke, fumes, arc glare and it is an eco-friendly welding process. This paper contributes on the various applications of FSW and related research findings in the field of materials joining.

Key Words: Friction Stir Welding, Aluminium, Magnesium, Stainless Steel, Tensile Properties, Microstructure

ESAB India Award: best technical paper presented in NWS 2010 Kolkata for a work done in India
Presented by
M. Divya, C.R. Das, S.K. Albert, V. Ramasubbu, A.K. Bhaduri and P. Sivaraman
Materials Joining Section, Materials Technology Division
Indira Gandhi Centre for Atomic Research,
Kalpakkam 603102, Tamilnadu

“In-situ weld repair of cracked shrouds of turbine and characterization of the weld joint”

Cracked shrouds of the 3rd stage of a Low Pressure turbine was in-situ repaired by removing the cracked pieces of the shroud and welding new shroud pieces to the existing shroud. The shroud material was made of AISI 414 martensitic stainless steel (SS), and the repair welding was carried out using ER 410NiMo filler wire. The tenon heads of the blades, which were removed for carrying out the in-situ repair, were also built-up by weld deposition. The repair welds were subjected to in-situ two-stage post weld heat treatment (PWHT) as required for the 414 SS material and the 410NiMo weld metal. For prior to simulation of the constraints of actual in-situ repair, a mock-up piece was made using the same blade material, welding consumable, welding procedure and PWHT as were to be used for the actual repair.
After successful completion of the repair, the mock-up piece as well as separate weld pads prepared using the shroud material and ER 410NiMo consumable were subjected to detailed microstructural characterization and mechanical properties testing to generate data on the properties of the repair weld now in service. The paper discusses the details of the in-situ repair and results of the characterization of the weld joints.
Results confirm the repair weld has adequate strength and ductility. The turbine with repair welded shrouds has been performing satisfactorily since 2008.

Key Words : Repair welding, Turbine shroud, PWHT, Supermartensitic stainless steels.

D K Sarma

AGM (Marketing),
ESAB India Limited ,
Ambattur, Chennai

“Hybrid Laser Welding : Process Advantages and Application for Shipbuilding”

Hybrid Laser Arc Welding (HLAW) combines the deep weld penetration and low heat input associated with laser welding with the power efficiency and superior gap tolerance of GMAW to create a new welding alternative. Adding GMAW in tandem with the laser, with the addition of a relatively modest amount of filler metal, creates a wider weld bead capable of bridging much larger weld gaps, up to four times as wide as conventional laser processes can handle. Latest innovation in this process is to combine the hybrid laser welding technology with the deep weld penetration and low heat input associated with laser welding with the excellent weld properties and superior gap tolerance of Gas Metal Arc Welding (GMAW). A radically new welding alternative, it produces extremely narrow and deep welds at very high travel speeds. In a single pass, such a process can often achieve what might require multiple weld passé using a conventional fusion welding process. Hybrid laser welding has been in use for several years in a number of the most advanced shipyards to build ship decks and bulkheads. Several systems in Some of the technology's most exciting contributions are found in new design capabilities, such as the metal sandwich panel, that were not practical until the advent of newer welding technologies. Sandwich panels can be simply defined as a three-layer structure that consists of two thin, outer skins of high-strength material separated by a low-density and low-weight core material. Several works revealed the following advantages of sandwich panel structures, including u to 50 percent weight reduction compared to conventional steel construction methods and improved energy absorption and damage tolerance.

Key Words : Hybrid Laser Welding, Tandem, GMA, Sandwich Panel