Pump & Pump Piping

PUMPS & PUMP PIPING By, Sandeep More Associate Engineer Piping Department Date 4th Dec 2006

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Pump -

Introduction to Pumps Classification of Pump Industry Codes & Standards Selection Criteria for Pumps NPSH & Cavitation

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Definitions

Pump Piping n n n n n n n n n n n n n n n

Suction piping for horizontal pumps Discharge piping for horizontal pumps Arrangements of piping for pump handling hot suctions. Side suction & side discharge pump Vertical In line pumps Vertical pump (Wet Well pump) Vertical Barrel type or Cane pump Multi Service pump Reciprocating pump Piping Metering Pump Pumps in the Tankage Area Auxiliary pump piping arrangement Pipe vent & drain System Pump Location & Arrangement Pump Surrounding Support

Intoduction To Pump : Definition : Pump is a mechanical device used to add kinetic and potential energy to a liquid for the purpose of moving it from one point to another. This energy will cause the liquid to do work such as flow through a pipe or rise to a higher level and Pump gives pressure to fluid passing through it and discharges the fluid to the outside.

Classification Of Pump : •

Pumps are classified on the basis of :The applications they serve, • The liquids they handle, • Orientation & Construction • No. of stages, No. of casings, Type of couplings (Rigid , Flexible)

1) Dynamic 2) Displacement

Dynamic Pumps :

In which energy is continuously added to increase the fluid velocities within the machine to values greater than those occurring at the discharge such that subsequent velocity reduction within or beyond the pump produces a pressure increase

Displacement Pump :

In which energy is periodically added by application of force to one or more movable boundaries of any desired number of enclosed, fluid-containing volumes, resulting in a direct increase in pressure up to the value required to move the fluid through valves or ports into the discharge line

Other Classification : 1) Classification by suction type : - Single suction type - Double suction type (for big volume pump) 2) Classification by the pump installation method : - Vertical pump type - Horizontal pump type

Classification by structure and operation method :

Type

Classification by structure

Classification by operation method

Specifics

Reciprocating pump

- Piston pump - Plunger pump - Diaphragm pump

This type of pump sucks in fluid through reciprocating movement of piston or plunger, and discharges fluid by pressing with required amount of pressure. It is used when high pressure is required even though the amount of discharge is small.

Rotary pump

- Gear pump - Screw pump - Vane pump

This type of pump sucks in fluid through the rotation movement of rotor, and has the advantage of little pulsation due to the special characteristics in operation.

Positive displacement pump

Centrifugal pump

- Radial flow - Volute pump - Mixed flow pump - Axial flow pump

This type of pump transfers energy to fluid through centrifugal force by impeller rotation or through the changes of size and direction of section area of passage, and converts velocity energy pressure energy in volute chamber or diffuser.

Special pump

- Jet pump - Gas lift pump - Wesco pump

This type of pump has a efficiency and is not used except for a special purpose.

Kinetic pump

Centrifugal Pump : A centrifugal pump transforms mechanical energy from a rotating impeller into a kinetic and potential energy required by the system.

Horizontal Centrifugal Pump

Centrifugal Pump

Reciprocating pumps : •

These are commonly used to move viscous liquids, inject chemicals or additives into a system.

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Reciprocating pumps are used where a precise amount of liquid is required to be a delivered, also where the delivery pressure required is higher than can be achieved with other types.

Reciprocating Piston Type Pump

Horizontal & Vertical Reciprocating pump

Rotary Pump : Rotary pumps are used to move heavy or very viscous fluids such as grease, asphalt, heavy fuel oil and sometimes heavy crude oils.

Gear Pump

Screw Pump

Industry Codes and Standards : Ref : GEMS P-G-2 American Petroleum Institute (API) 1.

610, “Centrifugal Pumps for Petroleum, Heavy Duty Chemical, and Gas Industry Services”.

2.

674, “Positive Displacement Pumps - Reciprocating”.

3.

675, “Positive Displacement Pumps - Controlled Volume”.

4.

676,“Positive Displacement Pumps (Rotary)

5.

677. “General Purpose Gear Units for Refinery Service”.

6.

681, “Liquid Ring Vacuum Pumps”

7.

682, “Shaft Sealing Systems for Centrifugal and Rotary Pumps”. American Society of Mechanical Engineers (ASME)

1.

B73.1M, “Horizontal End Suction Centrifugal Pumps for Chemical Process”.

2.

B73.2M, “Vertical In-Line Centrifugal Pumps for Chemical Process”

3.

Process Industry Practices (PIP)

1.

RESP73H-97, “Specification for Horizontal End Suction Centrifugal Pumps”.

2.

RESP73V-97, “Specification for Vertical Centrifugal Pumps”.

Selection Criteria For Centrifugal, Reciprocating, And Rotary Pumps

Definitions 1.

Casing, Axially Split – Pump case split parallel to pump shaft.

2.

Casing, Radially Split – Pump case split transverse to pump shaft axis.

3.

Diffuser – Pump design in which the impeller is surrounded by diffuser vanes where the gradually enlarging passages change liquid velocity head into pressure head.

4.

Double Acting – Liquid is discharged during both forward and return strokes of the piston.

5.

Duplex – Pump with two plungers or pistons.

6.

Head, Acceleration – Pressure change due to changes in velocity in the piping system.

8.

Impeller – Bladed member of rotating assembly of a centrifugal pump which imparts force to liquid.

9.

Net Positive Suction Head (NPSH) – Total suction head in meters (feet) of liquid absolute determined at suction nozzle and referred to datum elevation, minus the vapor pressure of liquid in meters (feet) absolute. The datum elevation is the shaft centerline for horizontal pumps, the suction nozzle centerline for vertical in-line pumps, and the top of the foundation for other vertical pumps.

10.

Net Positive Suction Head Available (NPSHA) – NPSH in meters (feet) of liquid determined by Purchaser for the pumping system with the liquid at rated flow and normal pumping temperature.

11.

Net Positive Suction Head Required (NPSHR) – NPSH in meters (feet) determined by Supplier testing, usually with water. NPSHR is measured at the suction flange and corrected to the datum elevation. NPSHR is the minimum NPSH at rated capacity required to prevent a head drop of more than 3% (first stage head in multistage pumps) due to cavitation within pump.

12.

Recirculation – Controlling the quantity of flow through a pump by bypassing discharge liquid back to suction.

14.

Simplex – Pump with one plunger or piston.

15.

Single Acting – Liquid is discharged only during forward stroke of the piston.

16.

Throttling – Controlling flow rate by reducing cross-sectional flow area, usually by partially closing a valve in the discharge piping.

17.

Total Differential Head (TDH) – Pressure required in meters (feet) of head that the pump must produce. The head at the discharge pump flange minus the head at suction flange.

18.

Triplex - Pump with three plungers or pistons.

NET POSITIVE SUCTION HEAD (NPSH) • The net positive suction head (NPSH) is the absolute pressure in excess of the liquid vapor pressure that is available at the pump suction nozzle to move the liquid into the eye of the impeller. •

The difference between NPSHa and NPSHr is less than 0.3 ∼ 1.0m at the time of checking vendor data sheet [ that is, NPSHa NPSHr〈 (0.3 ∼ 1m)], decision on NPSH test shall be made according to Engineering Specification SESGA-201E and API 610.

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Pumps where difference between NPSHA and NPSHR is less than 0.6 meter are not acceptable.

• The diameter of the pump suction port is usually bigger than the discharge or exit diameter in order to minimize the kinetic energy head entering the pump, because this kinetic energy decreases the maximum suction lift and enhances cavitation.

《 Pump Differential Head 》

10 H 〓 (Po Ps) × ──── Sp.Gr Where, H : Head (m) Ps : Pump suction pressure (㎏/㎠) Po : Pump discharge pressure (㎏/㎠) Sp.Gr : Specific gravity at pumping temperature

《 NPSH Required 》 NPSHr 〓 σ× H Where, H : Pump differential head σ : Cavitation coefficient of Thoma 《 NPSH Available 》 10 NPSHa 〓 (P1 P2) × ─── △P ＋ H Sp.Gr Where, P1 : Pressure at suction liquid level (㎏/㎠) P2 : Vapor pressure at suction temperature (㎏/㎠) △P : Pressure drop in suction line (㎏/㎠) H : Height between the normal liquid level and pump centerline (m)

CAVITATION

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Definition: Knocking due to formation and subsequent collapse of vapor bubbles. (Indication: Noise)

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Cavitation is caused by the formation of vapor bubbles in a high-velocity, low-pressure region and by the subsequent collapse when the bubbles move to a higher pressure region.

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Cavitation can cause excessive erosion and vibration.

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With moderate cavitation in a centrifugal pump, the pump will sound as though it is pumping gravel or a slurry of sand and gravel.

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Severe cavitation will cause the discharge pressure to fall and become highly erratic and produce both flow and pressure pulsation.

Cavitation occures due to : • Pump cavitation can result from insufficient available NPSH • High pump-suction velocities and long piping increase pressure fluctuations in the pump. • Vacuum systems seem more prone to unpredictable cavitation than pressure systems. Methods to avoid Cavitaion: NPSHa (P(suction) - P(saturation) >= NPSHr Increase NPSHa by

- Increase pressure at suction of pump - Decrease liquid temperature - Reduce head losses - Reduce NPSHr (Depends on Impeller inlet, Impeller design, Pump flow rate, impeller speed, type of liquid)

PUMP PIPING

Suction Piping for Horizontal Pumps :Line Size : Suction piping is one or two line sizes larger than the pump suction nozzle size. Flexibility of Suction Lines : • Piping flexibility affects pump location. • Pump suction lines should be as short as possible, but with enough flexibility. • If possible , do not overlap the pump and pipe support foundations, as it causes structural design problems in combining foundations.

Suction Line Fittings : • Reducers should be as close as possible to the pump suction nozzle so that pump suction will not starved. • Use Eccentric reducer with Flat Surface up. (FSU) • Always use long radius elbow.

Air pocket formed along upper side of pipe by concentric reducer.

Strainers :•

Strainers will be located between pump suction block valve and pump. Type of strainer 1) Temporary strainer 2) Permanent strainer Conical strainers are longer than the basket type. These are used on suction lines 2” and larger. For basket and conical types a removable spool piece must be provided downstream of suction block valve Flat strainers use with very short suction lines where no debris is expected

Bathtub or tee type strainers as most expensive , it does not require unbolting and removing spool piece to remove the strainer.

Y- type strainer to permit servicing of the strainer. Also, a blow-off connection may be provided in the end cap to flush the strainer.

Block Valve :• Suction line should have positive shut off valve, use gate valve at the Up stream of strainer. • Pump valves are operating valves, thus keep them as low as possible

Consideration of Cavitation n

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Cavitation occurs when NPSHr is larger than NPSHa. Cavitation reduces the performance of pump, causes vibration or noise and corrodes the materials. Therefore, minimize pressure loss on pump piping and, care shall be taken to avoid drifting on the nozzle. Minimum required straight pipe on suction nozzle to prevent drifting Suction type End suction

Side suction

Top suction

D- Suction Nozzle Size

Required straight pipe on suction 2D ∼ 3D

Single suction

2D and over

Double suction

10D and over or insertion of rectifying plate

Single suction

2D and over

Double suction

10D and over

Remarks See figure 1.

See figure 2-1 and 2-2.

See figure 3.

Consideration of straight pipe at suction side is not necessary for straight-up or straight down.

Figure 1. End suction piping

Figure 2-1. Side suction piping

Or inserts rectifying plate (eccentric suction : 2D and over)

Figure 2-2. Side suction piping

Single

Single suction : 2D and over Double suction : 10D and over

Figure 3. Top suction piping

Consideration of air pocket on suction line 1) Allow approximately 1/20∼1/50 of slope on suction line toward suction resource if suction resource is lower than pump suction nozzle.

2) Allow 1/20 and over of slope on suction line toward pump at vacuum tower.

1/20 and over

3 ) If gate valve is to be installed on the line whose suction resource is located lower than the pump suction nozzle, valve stem shall be horizontal.

Suction piping on tower or vessel : Vortex breaker is installed on tower or vessel nozzle connected to pump nozzle.

Typical Arrangement Drawing 1. PUMP SUCTION LINE

Horizontal

Vertical

Following diagrams indicate correct and incorrect methods of attaching suction piping.

Shows proper method of connecting pump suction to a suction header in order to avoid air pockets.

A) Horizontal ell directly into pump suction results in an unbalanced thrust on pump bearings. (B) Use spool piece 3 pipe diameters long or long radius ell with center vertical vane. (C) May be installed with or without spool piece but 2 pipe diameters spool is preferred. - Flexibility of pipe for pump alignment after piping Represents a common error made suction piping to a centrifugal pump by placing piping over an embankment of a reservoir, or other obstruction.

Discharge Piping for Horizontal Pumps :• Line Size :

Discharge nozzle size is normally smaller than the suction nozzle size.

• Discharge Line Fittings : • Normally we use concentric reducers in the discharge. • But if a clearance problem comes up between the suction and discharge piping , then we use o eccentric reducer • A pressure gauge is located in the discharge line, and should be upstream of the check and gate valves • Check Valve is used in a pump discharge line to prevent backflow in to the pump causing the impeller to turn backwards and possible ruining the bearings. • Block valve Isolate the pump from piping to provide maximum access for both in place for maintenance or removal.

Pump Discharge Line 1)

1 1/2 NB and Under 2) 2 NB and Larger

Use Swing / Ball Type Check valve

Use Hinged flapper Check valve

3)

4)

5)

For Higher line size 8” and above

Handling Hot suctions :

When header going to the two pump is at same elevation as suction nozzle.

These are used for very hot larger piping

If vessel suction nozzle is higher

Side Suction And Side Discharge Pump (For utility& Water Lines) n

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These are used for large duty differential pressure and large bore lines, the pressure difference between the pump suction and discharge , and are usually multi-stage pumps, the liquid going through several stages of increasing the pressure before reaching the side discharge nozzle. No of ells should be optimize allowable nozzle loading. The two-diameter pup can be eliminated if the elbow from the suction nozzle is horizontal.

This pump is horizontal split case . The top case can be removed for maintenance on this type of pump . keep the top of the pump clear.

Vertical In-Line Pumps : ( Hydrocarbon Services) The main advantage of this type of pump is to •

Eliminate many stress problems

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Location when there is no foundation required

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This type of pump is mounted directly into the pipe line. For smaller sizes, the piping system supports the pump and motor.

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For heavy or Larger size in-line pumps foundation will be required

Vertical Barrel Type or Can pump ( Dry well Pump ) : ( CBD Tank ) • This type of pump is installed in cooling tower water circulating service, retention ponds and suction is taken from a sump below grade. • In most cases, there is no suction piping to be considered, but the discharge line must be routed to ensure good access for pump maintenance

Multi - Service Pumps :•

Pumps can be used for more than one service, such as pulling suction from one source and discharging to three different locations or multi-service suction, which using a pump for more than one service.

Multi – Service Pumps

Reciprocating Pump Piping : • These lines should run close to the ground so that hold-downs can be used. • Suction and discharge piping to positive displacement reciprocating pumps shall contain hold down restraints on piping to minimize the potential of pulsation loading on pump nozzles should pulsation dampeners become inoperative. • To minimize the damaging effects of water hammer and other impulse type loading on pump nozzles, Use swing type check valves in discharge lines in the vertical position above rigidly supported elbows so that hammer loads may be distributed to grade or steel.

Reciprocating Pump Piping

Metering Pump : •

These pumps measured accurate flow rates that can be adjusted in operation to The me provide a wide range of varying flow rates.

•

Metering system is to control liquid discharge under a variety of back pressure conditions according to precise volumetric requirements.

• Since metering pumps permit little or no backflow, they are especially useful for injecting liquids into containers or flow lines against high pressures.

Reciprocating Metering Pump

Installation of Dampers and Back Pressure Valve

Pulsation Damper : The damper contains a diaphragm or bellows isolating the metered liquid from an air or gas padded chamber. its use eliminates hydraulic hammer, established more favorable NPSH conditions on the inlet side of the pump, and allows use of smaller pipe size by reducing peak liquid velocity and acceleration.

Pumps in the Tankage Area : For location of pumps in the tank farm area: 1. Group together if economical 2. Make accessible for maintenance and operation 3. Locate outside of dyke area In the routing of the suction lines, the preferred method would be to drop from the tank to the pumps. Avoid a direct run from the tank into the suction nozzle. This can cause problems in overstress of the pump connection. Support of Piping In the tankage area, the supporting of piping is normally by: • Pipe sleepers • Field supports

Auxiliary Pump Piping Arrangement : n

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Many pumps have auxiliary piping that is supplied by the vendor or the engineering contractor . When pump fluid is used a line is attached to the vent connection on the pump case. The circulated fluid must be sent back to the pump stream and return to the seal to pump internal clearances. In viscous or high temperature hydrocarbon liquids the seal fluid medium circulates from an external source through connections on the pump seal . This medium may be clean gas or oil . In fig the cooling water in and out of this particular pump is from above grade , however many cooling water systems are below grade so the piping layout designer must find suitable location for this connection.

Auxiliary Pump Piping

Pipe Vent And Drain System : • Are provide to escape air or vapour trapped in the casing.

Seal Flushing

PIPE VENT AND DRAIN SYSTEM FOR PUMP:

Pump Location & Arrangement : n

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Install on the place where access is easy during the operation. Sufficient space shall be provided at and around pumps to enable maintenance and removal of all internal and external parts. The minimum walkway clearance around pumps will be 2'-6”. The pump should be located as close as possible to the source of suction. The main reason for this is to minimize pressure drop. This keeps line sizes and equipment elevations to a minimum.

Minimum clearance of 3'-0" is required between pumps, adjacent equipment, foundation or other obstructions. Pumps should be located inboard of overhead pipe rack as much as possible in order to save the required plant area.

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For maintenance of the pumps located under the pipe racks or steel structures, maintenance beam or hook shall be planned upward of the pump unless; (1) Access way of maintenance vehicle is provided under the pipe rack. (2) Access of automobile crane is possible. Maintenance space 1000 mm required around pump and without major disassembly. Pumps shall generally be lined up in parallel with the pipe rack to maintain a uniformity of location. Pump discharge points to be fixed in a line below pipe rack and to be about 500 mm away from pipe rack bay. In hydrocarbon or other flammable fluid service, threaded construction shall not be used for piping connected to pump, including branch piping within 6 feet of pump suction or discharge flanges or through suction or discharge block valves, which ever is greater. Socket weld unions are acceptable.

Pump Spacing & Height of Pump foundation n

Pump Spacing :-

Suction pipe size (B) Pump spacing (mm) n

Up to 2

2-5

1500

2000

6 - 10 12 - 14 16 - 18 2500

3000

4000

Height of pump foundation :Height of pump foundation shall be 100∼300mm from ground level or floor level if it is on the paving or inside of building. But it shall be 300∼500mm for the area where flood is expected.

Others

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1) By-pass line which is installed on pump discharge line shall be routed without pocket. 2) Avoid installation of chemical or water supply line near the suction nozzle of reservoir so that air shall not be sucked in.

Pump Surroundings Support :n

Support regarding of eccentricity of pump : (1) Support shall be installed so that pipe and valve may not load on the pump nozzle.

(*) Support nozzle surroundings. (But, do not exceed 1m.) (2) Suction line and discharge line shall be supported respectively.

(3) If support is installed right close to suction or discharge nozzle, it shall be minutely adjustable type so that centering can be convenient.

(4) A support installed around suction or discharge nozzle shall be such a type that piping can be removed and pump can be dismantled easily.

Un-necessary support with respect to the load on pump nozzle :Although support would not seem to be necessary with respect to the load on pump nozzle, indicate it on the drawing considering the temporary support of piping during the time of pump maintenance.

Thank you