Checking corrosion to prolong the life of metals

Dhiraj Kumar Singh, who grew up in landlocked Ghaziabad, has always been fascinated by the sea. And so it comes as no surprise that the research project he is pursuing at the IITB-Monash Research Academy could have a huge bearing on the ocean-worthiness of mammoth structures in saline water like ships and oil rigs.

Offshore structures susceptible to stress corrosion cracking

The Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries, and graduate research scholars here study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

Dhiraj's project—under the guidance of Prof S K Maiti, Prof Raman Singh, and Prof Tanmay K Bhandakkar—is called 'Modelling and Experimental Studies of Hydrogen Assisted Stress Corrosion Cracking (HASCC) in Steel Weldments'.

HASCC causes premature failure in many metals used in engineering construction, explains Dhiraj. "It occurs due to the combined effect of corrosion-assisted hydrogen generation and stress-strain environment in the metal. The assessment of crack growth rate under such conditions is critical to assess the safety and life of machines and structural components, particularly in the marine and petrochemicals industries."

Dhiraj is closely studying the interaction between the evolved hydrogen and the stress-strain field, so as to be able to predict crack propagation in structural steel and its load-bearing capacity.

Finite element based modelling of crack propagation under HASCC

Modelling crack propagation under HASCC is challenging because crack propagation and hydrogen diffusion influence each other; hydrogen concentration affects the fracture strength of metal, and the stress field influences the hydrogen diffusion kinetics. The most popular mechanisms to explain how hydrogen affects the fracture properties of metals are Hydrogen Enhanced Decohesion (HEDE) and Hydrogen Enhanced Localised Plasticity (HELP).

Steel weldment, on the other hand, presents a complicated problem because of the existence of three distinct material zones—base metal, heat affected zone (HAZ) and the weld centre. Not much modelling and experimental studies have been reported in this area, precisely why Dhiraj is excited.

"Welding has a vital role in engineering construction and is widely employed in the marine industry, petrochemicals and process plants, hydrogen fuel storage and transportation, etc." he says. "Industry can benefit hugely by my work. Not only in design and development, but also to help prevent catastrophes during operations and work out maintenance schedules. I plan to propose reliable numerical models for HASCC crack growth prediction. Though experiments cannot be entirely eliminated, accurate modelling can help reduce them to a significant extent. This will help industries to predict fracture behaviour of structures quickly at a reduced cost."

Watching Dhiraj's progress closely is the Academy's CEO, Prof Murali Sastry, who says, "The IITB-Monash Research Academy is an exciting chapter in Indian-Australian relations that will see both countries creating binding links. This will enable us to tackle the research challenges that lie ahead and generate some long-lasting high impact outcomes for society. Dhiraj has exhibited immense potential—he joined our PhD programme with just a BTech qualification. I'm sure we will hear a lot about his work in the years to come."

Research scholar: Dhiraj Kumar Singh, IITB-Monash Research Academy

Project title: Modelling and Experimental Studies of Hydrogen Assisted Stress Corrosion Cracking in Steel Weldments

Supervisors: Prof S K Maiti, Prof Raman Singh, Prof Tanmay K Bhandakkar

Contact details: dhiraj2905@gmail.com

The above story was written by Mr Krishna Warrier based on inputs from the research student and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.