LINE PRESSING & LINE DISPLACEMENT - 2 WAYS TO ENSURE PRODUCT LOSSES ARE MINIMISED

Dear Petrol Inspector, 

Today, let us look at 2 great ways to ensure petroleum product losses are minimised when discharging from vessel to shore tank farms. They are Line Pressing and Line Displacement.

Let us start with Line Pressing.

1. Line Pressing: Another common name for this is Line packing. This procedure assumes that the designated pipeline system is tight and able to withstand pressures applied during line press operations without loss of line pressure as determined by pressure readings from a calibrated pressure gauge from the vessel. This procedure is invalid with any pipeline system that does not meet this tightness recommendation. To apply the line press method (or the line pack method), perform the following steps consecutively. 

Step 1 - Close the valve at the shore tank. Open the vessel's manifold, COT tank (better just one) and pump valves, and gauge the tank before line press. Measurements may be taken using either reliable automatic gauging equipment or manual measurement equipment. 

Step 2 - Start the pump and run it until the discharge pressure stabilizes and/or reaches a predetermined pressure. The predetermined pressure should be higher than the maximum static pressure available on the system. 

Step 3 - Isolate the pipeline to prevent backflow and stop the pump. 

Step 4 - Once the pump has been shut down. record the pressure and re-gauge the COT using the same gauging method as that used for the opening measurements. Record the tank product level. 

Step 5 - If the tank product levels before and after the line press are within 1/8th inch (0.003 meters) of one another, pipelines may be considered liquid-full and no correction is necessary. 

Step 6 - If the COT liquid levels before and after the line press differ from one another by more than 1/8th inch (0.003 meters), relieve the line pressure into the tank until the pressure at the highest elevation is slightly above product vapour pressure and then repeat the test. If the tank product levels before and after the second line press differ from one another by less than 1/8th inch (0.003 meters), pipelines are now full of liquid because condensible vapours have been re-liquified and no further correction is necessary. 

Step 7 - If the tank liquid levels before and after the second line press differ from one another by more than 1/8th inch (0.003 meters), either the line fill condition may be corrected or - with the agreement of all parties - gas volumes may be estimated by procedures and calculations. 

Step 8 - For purposes of line fill verification, the designated pipeline system may be considered full if the difference between the volume gauged before line press and the volume gauged after line press is within measurement precision. Note: This does not ensure that voids equal to compressed gas volumes less than measurement precision do not exist in the line.

Now let me give you time to digest this. We shall talk about the Line Displacement tomorrow. 

Till then - Keep Inspecting properly!