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Before DOT cylinder maintenance tasks can be done—such as replacing valve or fitting or checking the tare weight of the cylinder—it may be necessary to evacuate propane liquid and flare the propane vapor.
In this module, you will learn to identify:
(1) procedures for evacuating liquid propane from cylinders
(2) procedures for conducting vapor flaring operations
If the cylinder is evacuated of liquid propane for the purpose of comparing its weight to the manufacturer’s stamped tare weight as part of requalification, draining it of liquid is all that is required. It can remain pressurized with vapor for the purposes of tare weight comparison and requalification.
If however, the cylinder must be de-pressurized in preparation for valve or fitting replacement, the vapor must be reduced to near atmospheric pressure. That process may require the flaring of vapor.
Figure 9. Recommended Site for Flaring Containers (At Bulk Plant)
Although the flaring operation is simple, it does involve an open flame. As a result, certain safety precautions should be followed when selecting a site for flaring the container. These safety precautions will limit the danger
of an accidental fire while the flaring burner is operating.
It is important to select a burner with both a built-in shutoff and a regulator. This allows for adjustment of the output of the burner and prevents any excessive withdrawal from the cylinder or tank being flared.
Remember, excessive withdrawal could easily cause the tank or cylinder to temporarily stop vaporizing enough gas to supply the burner. This condition may be noticed when a frost line appears on the container, yet sufficient liquid may remain to re-pressurize the container when it regains heat from surrounding air.
During Step 6, observe the pressure gauge on the service valve (or purging adaptor). When the pressure drops below 15 psig, temporarily shut down the burner and allow the pressures in the tank or cylinder to increase. (Because of the high demand of the burner, the container may refrigerate during the flaring operation. If a frost line develops on the cylinder, temporarily shut down the burner and allow the pressure in the container to increase.)
When the vapor pressure no longer increases above 15 psig, flare the remaining vapor until the burner extinguishes.
Flaring operations should incorporate the following safety practices and recommendations:
1. Flaring operations should never be left unattended and qualified personnel should continuously monitor flaring equipment and conditions.
2. If qualified personnel must leave the flaring operation for any reason, the operation should be shut down and the valve(s) on the container being flared should be closed.
Check with your supervisor or any company-specific procedures that may apply to flaring operations.