Page 28 - CCPS Golden Rules - Chloral Alkali

Golden Rules for Chlor-Alkali

Golden Rule #9: Always protect against isolating liquid-full chlorine lines.

❖ Why:
Liquid chlorine has a very high thermal expansion coefficient [12].
Liquid-full lines that are isolated at each end and equipment without adequate relief will see very high
pressures (thousands of psig) with a very small temperature increase [14] [16].
When Chlorine is trapped in a closed system, rising temperatures cause the liquid to expand and exert
pressures that can overcome the pressure rating of the containment system.
The pressure rating of liquid chlorine lines and equipment can be much lower than the pressure that can
result from thermal expansion; gasket, flange, piping and equipment failures (blowouts and bursting)
can be expected, releasing all the chlorine contained [12] [14] [16].
The released liquid chlorine will result in a gas cloud more than 460 times the volume of the liquid [12].
Incident History:

At around 05:00, a plant employee had completed the loading of a chlorine railcar. The employee
closed the chlorine valves and the employee began to prepare this next railcar for loading. It was
expected that the employee would start loading again within the next hour. At approximately 06:00,
a 375 psig rupture disc in the chlorine railcar loading piping system burst. The rupture disc should
have reduced the pressure in the line by directing the chlorine into the expansion chamber keeping
the chlorine fully contained. However, the wrong rupture disk holder was used and chlorine was able
to escape out of a hole at the back end of the assembly. 110 pounds of liquid and gaseous chlorine
were released during the approximately 15 minutes it took operators responding to the emergency
and close the valve that supplied chlorine to the rail loading area [40].
❖ How – General:

Avoid operations and designs that would routinely trap liquid chlorine.
Develop a standard to address how to isolate liquid filled lines and equipment to prevent over
pressurization.

Updated January 2024 Page 25 of 28