Shares of Mangalore Refinery and Petrochemicals Ltd (MRPL) dropped 10% from recent highs on reports of a major fire at the refinery's Coker hydroheater unit, sending the stock to its sharpest single-session decline since the start of the fiscal year.

The blaze broke out at the hydroheater section of the delayed coker at MRPL's 15-million-metric-tonne-per-annum (MMTPA) complex at Mangalore, on the Karnataka coast of southern India, according to a CNBC TV18 report. MRPL, a subsidiary of upstream major Oil and Natural Gas Corporation (ONGC), had not issued a formal disclosure on the incident or quantified the impact on throughput at the time of the share price move.

What is a Coker hydroheater?

A hydroheater heats residue feed before it enters the coker drum, where it cracks into petroleum coke and lighter distillates. The hydroheater sits upstream of the drum and is critical to maintaining drum fill rates and cycle times. Damage at this node can sideline the entire coker train until tubes, headers and instrumentation pass inspection.

MRPL operates a single-train delayed coker configured to process residue from its refining slate. With Mangalore running above nameplate at recent quarterly turnarounds, any unscheduled outage at the coker removes the operator's ability to upgrade bottom-of-the-barrel barrels into coke and gas oil.

How is the market reacting?

The stock move is the cleanest signal traders have. A 10% pullback from the recent high equates to a roughly ₹15-16 billion swing in market capitalisation, given MRPL's float and free-tradable shares. The decline followed the CNBC TV18 report; the broader BSE Oil & Gas index traded broadly flat on the session, suggesting the move is asset-specific rather than sector-wide.

What does MRPL need to disclose?

Indian listing rules require MRPL to inform stock exchanges of any event with material price impact "as soon as reasonably possible." With shares down a tenth from the print high, the threshold has arguably been crossed. Watch for:

• A formal BSE/NSE filing with the cause of the fire and damage assessment
• Throughput guidance for the quarter, particularly coker feed rates
• Insurance and business-interruption disclosures if the unit is offline beyond a standard permit cycle
• Confirmation of whether the fire triggered any evacuation of nearby process units

How does this fit MRPL's recent operating record?

The Mangalore complex has run extended cycles between scheduled turnarounds in recent reporting periods, with the operator crediting better reliability for higher utilisation against the 15-MMTPA nameplate. An unscheduled outage at the coker would puncture that narrative and could force MRPL to revise margin guidance depending on repair duration.

Delayed cokers typically take 14-30 days to return to service after a hydroheater incident, depending on metallurgy checks and tube replacements. Each week offline at a 3-MMTPA-class coker removes roughly 580,000 barrels of residue processing capacity from the system.

What is the watch item?

The next event-driven catalyst is MRPL's exchange filing on the scope of damage. Until then, traders are pricing the outage at the worst end of historical hydroheater incidents, which have ranged from localised tube leaks lasting days to multi-month shutdowns following header failures.

A short-duration outage, with the coker back online within the next two to three weeks, would likely see the shares retrace the 10% decline in full. A multi-month shutdown, by contrast, would re-rate the stock lower and pull forward debate over whether MRPL needs fresh capex on the coker train ahead of any future residue-upgrading configuration.