PIPELINES VIJAY VADER

PROCESS PLANTS  Essentially handling liquid/gases/solids  Need to transport them from one stage to another.  Transportation is always done through closed conduits /pipes  Transportation systems consist of - Pumps - Compressors - Blowers - Piping networks associated with them.

Potential & Resistance for flow through Pipes  Potential : Elevation Difference between source and destination, pressure difference between source and destination.  Every fluid movement has to overcome the resistance. Typical resistances are : - Static (Increase in height) - Dynamic (Frictional Losses because of flow/ velocity) - Back Pressure depending upon the destination pressure.  Above resistances are overcome by using machines like pumps, compressor and blowers.

Potential & Resistance for through Pipes

Selection of Pipe Lines  Based on Line Size : - Volumetric flow rate is the basis for calculation. - Recommended velocities are available in literature / Engineering guide lines. - Principle involved is optimization between pressure drop and line size. ( i.e. Pumping cost and Capital cost )

Selection of pipe Lines Typical Recommended velocities : Type of FlowRecommended Velocity (m/s) Process Liquid Lines ( Pump Discharge) 1 to 3.6 Water Lines 1 to 2.7 Pump Suction Lines 0.3 to 2.1 Compressor Discharge Lines 21 to 30 LP steam Lines 8 to 41 MP steam Lines 13 to 70 HP steam Lines 16 to 83

Two Phase Flow  No proven and accurate method available for pressure drop calculation.  Various flow patterns possible depending on vapor-gas ratio, roughness, etc.  Typical Examples : - Furnace outlet lines, long gas transport lines containing condensable hydrocarbons.  Careful consideration for slug and plug flow.  Two phase flow can produce hammering and vibrations which could damage the pipelines.

Selection of Pipelines  Based on Service : - Pipe materials are selected based on service - Based upon temperature and pressure pipe material for suitable # rating and high or low alloy steel is selected. - Steam : Statutory requirements like IBR ServiceMaterial Normal HydrocarbonCarbon Steel Sour ( with H2S)NACE DM waterStainless Steel Sea WaterEpoxy Lined or GRP pipes CausticStress Relieved CS

Piping and Instrumentation Diagram  Most important document generated by Process Engineer.  P&ID is used as base document by Piping Engineer.  It gives following minimum details with respect to pipelines (Attached snapshot) - Source and Destination of pipelines. - Line Number : Typical Line No. appearing in P&ID Unit No. Fluid Seq. No. Line Size Pipe Class Ins. Type Insulation Code Thickness Z312 PAHC18203EC12AB150

Snapshot of P&ID

LDT ( Line Designation Table)  Compilation of all lines appearing on P&IDs in a tabular form.  Typical format is shown below :  Utilization of this document by Piping and Construction departments  Contains information required by construction group for testing.  It also includes information regarding piping color code and tracing requirements.

General guidelines for Pipe Routing  Avoid Pockets.  Provide high point vents and low point drains.  Ensure easy access for operation as well as maintenance of all valves and instruments.  Provide break flanges in pipes wherever removal of pipe etc. is envisaged for maintenance of equipment.  Avoid complicated routine of pump suction lines from NPSH requirements.  Safe Venting at high location.

Cross Country or Long Pipelines  Typically used for transportation of hydrocarbon from terminal to refineries OR refineries to storage depots.  Pressure Boosting stations at various locations.  Surge phenomenon results into high pressures in pipe lines.  Surge is caused by Pump failure, sudden closure of valve.  This phenomenon needs to be carefully analyzed to avoid mechanical failure of pipe.  This is further analyzed by using advanced software for transient analysis.