The main objective of passive fire protection coatings of vessels and structures is to slow down their heating-up process to ensure:
- Prevention of escalation to adjacent equipment including vessel/pipe rupture or BLEVE
- Prevention of excessive structural deflections and collapse
- Maintenance of functionality of safety critical systems (e.g. ESD valves, blowdown/flare systems, firewater piping, emergency power, etc)
Passive Fire Protection
Oracle Risk Consultants have been involved in several PFP optimisation and revaluation studies and have come to the conclusion that, in many cases, the philosophy of providing PFP has not been well defined and the downside of providing PFP, namely ongoing maintenance and unrevealed corrosion, was not fully taken into account.
Consequently, there has been a general move away from specifying PFP unless required for safety reasons - i.e, to prevent escalation due to stress rupture of adjacent process equipment or to protect critical structures (e.g. protect a flare tower such that it does not topple onto the living accommodation in a fire).
Although PFP can certainly limit the consequences of a fire and the potential for escalation, it only has a safety benefit if personnel have not been able to escape to a safe distance prior to escalation occurring.
A particularly severe escalation incident is a BLEVE which can occur when a vessel containing a volatile liquid heated to above its flash point ruptures causing a massive fireball and the potential for projectiles. The repture of high pressure gas piping is generally far less serious.
The potential for failure of process equipment in fires is a function many variables including material, steel mass, operating pressure, emergency blowdown profile, etc.
There has been a tendency for operators to only apply PFP if it has a proven safety benefit or a significant asset benefit, eg. to protect expensive equipment or to prevent the release of a massive amount of inventory (eg. from a pipeline).
Initial simplified calculations can be performed to determine the need for PFP based on consequence assessment of failure with no PFP in place based on the assumption that failure can occur.
More detailed fire duration and failure calculations can then be performed to determine the minimum extent of PFP required to prevent harm to personnel and to protect vital equipment using heat-up calculations in which the heat-up and loss of strength of the steel vessel wall can be compared with the internal pressure, accounting for blowdown, to determine whether the unprotected vessel would fail prior to depressurisation.