Unloading a bobtail cargo tank in metered delivery service at the bulk plant or an industrial installation requires strict compliance with DOT cargo tank unloading regulations.
In this module you will learn to identify:
1. Regulatory requirements for unloading cargo tanks larger than 3500 water gallons capacity in metered delivery service .
2. Procedures used for unloading a cargo tank in metered delivery service at the bulk plant or an industrial installation .
3.5.10Unloading a Bobtail Cargo Tank of 3,501 Water Gallons or More
DOT regulations require:• Cargo tank motor vehicles (CTMVs) with cargo tank water capacities of 3,501
gallons or more to be equipped with an off-truck emergency activation device with a query feature that will automatically shutdown a transfer operation lasting more than 5 minutes unless the unloading attendant responds to the query feature to extend the unloading period. The emergency activation device must be tested for proper operation at a distance of 150 feet from the vehicle within 18 hours prior to the first delivery of the day. (Figure 1.) If the test was not done as part of the pre-trip inspection or as part of the previous day’s post-trip inspection, do it prior to the cargo tank unloading operation .
Regulatory requirements for unloading cargo tanks larger than 3500 water gallons capacity in metered delivery service.
Figure 1. Off-Truck Remote Shut-Off Activation Device Test
Identifying Regulatory Requirements for Unloading Cargo Tanks in Metered Delivery Service
DOT regulations require:• The unloading operator to check those components of the cargo tank discharge
system, including delivery hose assemblies and piping that are readily observed during the normal course of unloading prior to the start of unloading operations. The purpose of the discharge system component check is to assure that they are of sound quality and without obvious defects detectable through visual observation and listening for leaks or other unusual sounds. (Figure 2.)
Figure 2. Checking Readily Observed Components of the Discharge System
Identifying Procedures Used for Unloading a Cargo Tank at a Bulk Plant or Industrial Installation
•CTMVs with 3,501 water gallon or larger cargo tanks in metered delivery service must be equipped with
•Emergency discharge control systems capable of shutting down the vehicle engine and stopping the flow of propane by the use of a remote off-truck emergency activation device with query feature, or
•These CTMVs may alternatively be equipped with a passive emergency shutdown system that will automatically shutdown the vehicle engine and stop the flow of propane within 20 seconds without human intervention in the event of a complete delivery hose break .
•CTMVs with 3,501 water gallon or larger cargo tanks in other than metered delivery service
•Must be equipped with a passive emergency shutdown system that will automatically shutdown the vehicle engine and stop the flow of propane without human intervention in the event of a complete delivery hose break.
Identifying Procedures Used for Unloading a Cargo Tank at a Bulk Plant or Industrial Installation
•CTMVs with 3,501 water gallon or larger cargo tanks in both types of delivery service (metered and non-metered) must be equipped with both— a passive emergency shutdown system that will automatically shutdown the vehicle engine and stop the flow of propane within 20 seconds without human intervention in the event of a complete delivery hose break, and an off-truck emergency shutdown device with query feature.
•For unloading operations of this last type of CTMV, the unloading attendant must utilize the type of emergency shutdown system that is correct for the type of delivery service used to unload the cargo tank.
Identifying Procedures Used for Unloading a Cargo Tank at a Bulk Plant or Industrial Installation
• The use of an ACME adapter (Figure 3.) may be needed to make the transition from the bobtail delivery hose assembly to the bulkhead piping. If the bulkhead is equipped with a permanent transfer hose, additional adapters may be required to mate with the transfer hose end adapters.
Figure 3. ACME Unloading Adapter
Note:
Procedures for unloading bobtails are based on practices commonly used in the propane industry, manufacturers' instructions, and provisions in NFPA 58. Before the filling operation, you should review bulk plant layout and operating procedures. This step is detailed in Modules 3.5.2. Make sure you are familiar with the bulk plant equipment, piping functions, and company operating procedures.
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
• Specific U.S. DOT unloading regulations that are appropriate to the CTMV emergency discharge control system must be applied. All required emergency discharge control system and delivery hose inspections and tests must be made before beginning the transfer operation.
• The off-truck remote emergency discharge system activation device must be in the possession of the unloading operator at all times during the unloading operation.
• The unloading operator must have an unobstructed view of the cargo tank and delivery hose to the maximum extent practicable, except during short periods when it is necessary to activate controls or monitor the receiving container.
• If bulk plant transfer hose assemblies are used, they must be inspected and determined to be sound and without rejection defects before the unloading operation is started.
• A qualified person must be in attendance at all times during cargo tank unloading.
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
WARNING
During transfer, wear appropriate protective gloves and clothing to prevent frostbite or freeze burn from exposure to liquid propane.
Step 1: Position the Cargo Tank Motor Vehicle . •Check area for hazardous conditions and possible sources of ignition. Sources of ignition capable of igniting LP-gas are not permitted near a point of transfer. If any are found, further operation should be delayed until the situation is corrected. Be sure the vehicle is equipped with an 18 lbs. B:C dry chemical fire extinguisher bearing a current inspection tag or decal.• Park vehicle at the unloading bulkhead in proper position to make the transfer. (Figure 4.) •Set the parking brakes and place chocks in front and behind a rear wheel to prevent rolling of the vehicle.
Step 2: Check the Liquid Level Gauges on the Bulk Storage Tank(s) to Assure Adequate Capacity To Receive the Propane Without Overfilling.
•Even if the plant has more than one storage tank, it must be determined how much propane can be safely added to each tank. If a single tank will not hold the entire load, calculate the distribution of the load among one or more additional tanks
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
• Gauge the contents of the plant storage tank with the rotary or float gauge installed in the tank head. Record the percentage reading on the company form or on a worksheet.
• Using the temperature and specific gravity of the propane in the bobtail cargo tank, determine the maximum permitted filling level in percent for the plant tank(s). Use 0.508 for the specific gravity if plant records do not indicate a different specific gravity. Record the result on the worksheet.
• Subtract the bulk storage tank gauge reading(s) from the maximum permitted filling level.
• Calculate the maximum amount of propane that can be added to the storage tank by multiplying the difference between the two percentage numbers by the water capacity of the tank in gallons. If, for example, the gauge on a 30,000-gallon storage tank shows that it is 40% full and its maximum permitted filling density at the present cargo tank temperature is 85%. Multiply the difference, 45% X 30,000 gallons. For our example, a single 30,000- gallon tank, 13,500 gallons can safely be added to the bulk storage tank, an amount greater than the propane capacity of the bobtail cargo tank. Throughout the unloading process, monitor the liquid level gauges of all bulk storage tanks to ensure that no tank is overfilled .
To determine the amount of propane each plant tank will hold safely:
Step 3: Connect the Bobtail Delivery Hose and the Bulkhead Vapor Hose Between the Bobtail and the Plant Bulkhead.•Review and follow company procedures for checking the operation of the ESVs installed in the plant. Be sure to include a check of the remote operators and all fusible links. If the ESVs will not operate properly, do not continue the transfer operation; notify a supervisor. Check the condition of each hose for any rejection criteria defect. (Refer to Module 3.5.5.)
Step 4: Open the Bulkhead Valves and Check the Hose Connections for Leakage.
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
Step 5: Insert a Meter Ticket Into the Bobtail Meter Register (or Begin the Meter Delivery Sequence on an Electronic Meter) and Reset the Meter for Recording the Transfer.
Step 6: Open the Required Valves in the Bobtail Discharge System, Engage the PTO, and Begin Pumping Using the Bobtail Pump.
Step 7: Stop the Bobtail Pump:•Without letting the pump run dry—when the liquid in the cargo tank has been transferred to the bulk storage tanks; or•Any abnormal operating condition or pump noises occur; or •If the maximum permitted filling level of any bulk storage tank is reached
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
Step 8: Close All Bulkhead and Bobtail Valves and Disconnect the Transfer Hoses. •De-pressurize the hose connections after closing the hose-end valves and the cargo tank and bulk head valves, then venting the trapped propane liquid and vapor •As the bobtail delivery hose assembly is retrieved and stowed in its travel position, inspect the full length of the hose deployed during the unloading operation as required by DOT regulations. (Figure 5.) •Remove the adapter (male ACME to female ACME) used to connect the delivery hose assembly and bulkhead and store it in the designated place •Replace dust covers on the bulkhead vapor hose, and the bobtail filling valve connector.
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
Step 9: Prepare the Bobtail for Travel. •Do a walk-around inspection of the bobtail to ensure that all hoses and tools used in unloading are properly stored.•Remove and stow the wheel chocks.•Start the engine and when ready, move the bobtail from the unloading bulkhead to a secure parking area inside the bulk plant.
Identifying Procedures Used for Unloading a Bobtail at Bulk Plants
