The complete failure of the fuel tank appears to be the cause of the massive leak that caused the launch postponement of India’s first home-made geosynchronous powered rocket in August.
Mr. Radhakrishnan [head of India's space agency] said while the expert committee had attributed the fuel leak to stress corrosion cracking of the tank filled with propellants, exactly why this happened was “a research problem” that remains to be investigated. The next GSLV mission will switch to a better aluminium alloy material for its propellant tanks.
Up to now the reports have been somewhat vague about the cause of what was clearly an extensive leak. This story tells us that the tank essentially failed. As they filled it with propellants, cracks apparently showed up everywhere, with fuel spewing out in all directions. As far as I can remember, I don’t think there has ever been a rocket tank failure quite this spectacular.
This suggests there were fundamental design flaws in the tank or very serious quality control problems in its manufacture. With the next launch attempt scheduled for December 15, I hope India has identified the source of this incredibly basic problem and taken action to prevent it from happening again.
Update: Reader Patrick Ritchie found this older article which suggests the failed tank was an old tank of a design that was “prone for delayed cracks”. The error here then was in using this substandard old equipment rather than a newer tank.