DP 3-3-3-4 Piping Design -- Process Considerations

DP 3-3-3-4

PIPING DESIGN Exxon Company, U.S.A. Marketing Distribution DESIGN PRACTICES

Page 1 of 2

PROCESS CONSIDERATIONS PROPRIETARY INFORMATION - For Authorized Company Use Only

Rev. 0.2

Oct., 1994

SCOPE This Design Practice covers process considerations for piping systems. It will serve as an introduction to more detailed discussions covered in Design Practices devoted to specific systems, i.e., additive injection, truck loading, etc.

REFERENCES DESIGN PRACTICES DP 9-9-1 DP 22-22-10

Atmospheric Storage Tanks Terminal Layout and Spacing

PRODUCT PIPELINE CONSIDERATIONS Most terminals are supplied by common carrier product pipelines shared by many companies. The design and operation of the terminal, therefore, must include provisions to receive product and send it to the appropriate storage tank without product degradation and disposal of interface. The pipeline operator is responsible for scheduling product batches and sequence. A proper schedule will minimize critical and non-critical interfaces to reduce product downgrading cost and prevent incompatible interfaces (distillate to gasoline) by inserting a kero buffer. Non-critical interfaces occur between batches of different grades of the same product, e.g., premium and regular gasoline. The higher grade product is cut into the lower grade. Critical interfaces occur between gasoline kerosene (treated as low flash) and distillate - kerosene (treated as high flash). Critical interfaces are sent respectively to low flash and high flash interface tanks for later reinjection to an appropriate product. Sending distillate to gasoline or vice versa would be incompatible from a product quality point of view. Densitometers are used to differentiate between products. Occasionally a remote densitometer is installed to provide advance warning for a product change with the final cut being made by the local densitometer. The factors which influence interface generation and growth are: 1.

Combination, if possible, of batches to maximize batch size.

2.

Product pumping sequence: A lighter product following a heavier product will produce a smaller interface than the reverse sequence. Secondly, the greater the density differences between batches, the greater the co-mingled zone or interface.

3.

Collection system design - manifold valve speed: The speed of the product manifold valves affects the initial size of the interface. The valves are interlocked and automatically controlled to start closing the first valve when the second valve is, for example, 25% open. Consequently, the speed of the valve affects the time that both valves are open.

4.

Pumping operation: Pipelines must be operated in turbulent condition to minimize interface growth. Streamline (laminar) flow will cause large interfaces because the product at the pipe wall is not flowing at all. Pipelines should be kept pressurized during any flow stoppage to minimize interface growth. Stoppages should be minimized where interfaces exist.

5.

Use of pigs or spheres to reduce interface is generally uneconomic.

Exxon Company, U.S.A.

DP 3-3-3-4

PIPING DESIGN Exxon Company, U.S.A. Marketing Distribution DESIGN PRACTICES

PROCESS CONSIDERATIONS PROPRIETARY INFORMATION - For Authorized Company Use Only

Page 2 of 2 Rev. 0.2

Oct., 1994

PIPE ROUTING CONSIDERATIONS Piping routing decisions are based on functionality, economics, safety and use of land area. Examples are:

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Pump suction lines should be direct, without vapor traps or vertical loops, etc.

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Lines passing through dikes must have protection against corrosion such as wrapped and coated or cased and sealed in another pipe.

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Piping for one group of tanks should not be routed through diked areas for a separate group of tanks to avoid increasing the risk from a fire.

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Tanks should be provided with separate inlet and outlet lines.

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In general, piping should be concentrated in pipeways located to preserve available area.

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It is often advantageous to route piping around the terminal periphery. Piping can be located close to the property fence without increasing fire risk or consequences.

REVISION HISTORY Date 1/94 ?

Revision 0 1

Description Issued as DP 3-3-3-4. ?

Exxon Company, U.S.A.