Pump Piping

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Reliance Rel iance Engineering A sso ciates Private P rivate Lim ited

PIPING DESIGN GUIDE

P-EP-PL-041-0A

Piping Design – Pumps

0

REV

DATE

ISSUED AS STANDARD

KS

MGC

MGC

REVISION

BY

CHKD

APPR

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CLIENT

RELIANCE RELIANCE ENGINE ENGINEERING ERING ASSOCIATES OCIATES PRIVATE LIM LIMITED ITED

Contents 1. Purpose............ Purpose...................... .................................. ................................. ................................. ................................. ................................. .................................. .......................... ................ 2. Scope.............. Scope........................ ................................. ................................. ................................. ................................. .................................. ................................. .............. .............. ............. .... 3. Codes Codes & standards standards ................... ............................ ............. .... .................. ............................ .............. .............. .................... ................... ............ ... ................... ......................... ...... 4. Defini Definitions tions ................................ ................ ................ ................................ ................ ................ .............................. .............. .................. .. ............................... ............... .................. .... 5. Different type of pumps 6. Pump piping layout 7. Pump piping supports 8. Auxiliary piping 9. Stress analysis for pumps

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Contents 1. Purpose............ Purpose...................... .................................. ................................. ................................. ................................. ................................. .................................. .......................... ................ 2. Scope.............. Scope........................ ................................. ................................. ................................. ................................. .................................. ................................. .............. .............. ............. .... 3. Codes Codes & standards standards ................... ............................ ............. .... .................. ............................ .............. .............. .................... ................... ............ ... ................... ......................... ...... 4. Defini Definitions tions ................................ ................ ................ ................................ ................ ................ .............................. .............. .................. .. ............................... ............... .................. .... 5. Different type of pumps 6. Pump piping layout 7. Pump piping supports 8. Auxiliary piping 9. Stress analysis for pumps

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1.

Purpose This specification covers general guidelines guidelines for for various pump piping layouts. Examples of various layout sketches are attached which will be helpful for the piping designer/engineer to implement implement a proper layout. These guidelines are developed considering plant safety, operation / maintenan maintenance ce aspects and meeting meeting statutory requirements requirements of various national and international codes/standards. The design must reflect consistency in approach in order to result in a quality design .

2.

Scope This This design guide is concerned concer ned with the design of piping layouts for various category of pumps. The Plant layout and Piping group is responsible for developing a comprehensive, safe and well thought out design. That includes meeting various codes, manufacturer and/or client requirements for nozzle loads on the pump as well as stress allowable for the piping system. Support of the piping system must be given careful consideration during the layout of the piping. This is a joint effort of the piping piping designer designer and the pipe stress st ress / support engineer. engineer. Proper design design of the piping must allow good access to the pump for operation and maintenance.

3.

Codes and Standards

a) P-GS-PL-003 b) P-SS-PL-015 P-SS- PL-015

Piping Design & Plant Layout . Specification Specification for Piping Piping Stress Analysi Analysiss

c) P-SS-PL-019 d) P-EP-PL-065 e) API-61 API-610 0

Pipe support standards. Small bore Pi Piping design Guide. Cent Centri riffugal ugal Pum Pumps for Petrol Petroleu eum m, Heavy Duty Chemical and Gas Industry Services

f) ASME B73.2

Vertical Vert ical inline inline pumps for chemical process proce ss service Horizontal Horizo ntal end suction suctio n pumps for chemical process service

g) ASME B73.1

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4.

Definitions

4.1

Safety Proper consideration for personnel safety shall be considered while doing

the piping layout/locating valves & strainers in such a manner that clear access is provided near pumps for operation/ maintenance as well as egress in an emergency. Care must be exercised not to create tripping hazards with auxiliary piping. piping. 4.2

Operation

Pumps normally require minimal minimal attention att ention during operation. opera tion. Valves, strainers etc must, however, be located for easy access. Where valves cannot be operated (i.e. above 2 meters) from grade, suitable platform shall be provided depending upon the operation requirement. 4.3

Maintenance

Piping Piping shall be arranged in a manner manner to allow adequate adequat e access to the pump avoiding excessive dismantling of the piping system to satisfy maintenance requirements. The coupling between the pump and its driver must be accessible for alignm alignment/dismantlin ent/dismantling g purpose etc. Pump Pump seal access must also be considered since seal failure is the most common cause of maintenance. 4.4

Allowable Nozzle Loading

The allowable nozzle loading is the maximum maximum amount of stress str ess that the pump suction and discharge discharge nozzles can withstand, as set by the vendor, client, or code .The discharge and suction piping piping cause considerable stress on the pump nozzles which shall be brought within the allowable nozzle loading by proper layout. 4.5

Net positive suction head ( NPSH )

The total to tal absolute suction head , in meters ( feet ) of liquid liquid ,determi ,deter mined ned at the suction nozzle nozzle and referred referred to the t he datum elevation, elevation, min minus us the vapour pressure of the liquid, liquid, in meters ( feet ) absolute. absolute. The datum elevation elevation is

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the shaft center line for horizontal pumps, the suction nozzle center line for vertical inline pumps and the top of the foundation for other vertical pumps. pumps. The manufacturer usually tests test s the pump with water at different different capacities, created creat ed by throt tling the suction side. side. When the first sign of vaporizatio vapor ization n induced cavitation occurs, occur s, and that pressure is converted converte d into head. head. This This head number is published on the pump curve and is referred as “ net positive positive suction head required ( NPSHr )” or sometimes sometimes in short as the NPSH. 4.6

Net Positive Suction Head ( available ) The available available NPSH is is the net net pressure availabl availablee in in a given given system based on vessel pressure and static head, minus the liquid vapor pressure and the functional losses in the system. The goal is to maintain equipment heights and minimize pump suction piping lengths, and bends to ensure that the available NPSH is greater than the required NPSH. Insufficient NPSH can reduce reduc e pump capacity capac ity and efficiency efficiency and lead to cavitation

4.7

Vapour pressure When the pressure in the pump suction line line falls falls below the vapour vapou r pressure of a liqui liquid d , the liquid liquid flashes, flashes, or o r changes changes to vapour. Because no ordinary ord inary pump can handle only vapour, liquid liquid flow to the t he pump falls falls off and the unit unit is is said to be vapour bound. bo und.

4.8

Cavitation Cavitation is the phenomenon caused by vaporization vaporizat ion of a liquid liquid inside a pump. When the t he pressure at any poin po intt drops below below the vapour pressure corresponding to t he temperature of the liquid liquid being pumped, pumped, vaporization of the liquid liquid will will occur. occur . Small cavities of vapour thus t hus formed move with the flow through the pump until a region of higher pressure is reached. The higher higher pressure causes the vapour cavities to collapse co llapse with tremendous shock on the surrounding metal.

4.9

API 610 (American Petroleum Institute) This standard standar d is based on the accumulated knowledge knowledge and and experience of manufactures and users of centrifugal pumps. The objective of this standard is to provide a purchase specification specification to facilitat facilitatee the manufacture and procurement of centrifugal pumps for use in petroleum, chemical, and gas industry services.

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RELIANCE ENGINEERING ASSOCIATES PRIVATE LIMITED

4.10

AVS(American Voluntary Standard) Pumps This standard, issued by the hydraulic institute, outlines several pumps with standard dimensions. They are interchangeable for a given size, regardless of who builds the pump, with no effect on foundation , piping design, or type of electric motor used.

5.

Pump Types Pumps are generally classified as Centrifugal, Rotary or Reciprocating pumps depending upon the process requirements. Pumps may be of motor driven or turbine driven type. Most commonly used pumps in the refinery industry are of Centrifugal type.

5.1

Centrifugal pumps Centrifugal pumps employ centrifugal force to develop a pressure rise for moving a fluid. The Centrifugal pumps will usually be of Horizontal, Vertical Inline, Vertical Can type. Following are some of the figures showing various type of pumps.

End suction – Top discharge pump

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Top suction – Top discharge pump

Side suction – Top discharge pump

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5.2

In the following sketches some of the important parts of pumps are marked like suction/discharge nozzles, bearing housing, seal gland etc.

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5.3

A typical centrifugal pump performance characteristic is shown below. Total head , power absorbed are plotted against flow. These are the working characteristics of the pump. Pump efficiency derived from flow, total head and power is also plotted against flow to locate the best efficiency point ( BEP ) and indicate the pump’s most effective operating range.

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5.4

Multistage pumps

Pump efficiency deteriorates rapidly as specific speed decreases. The problem now becomes one of devising a pumping arrangement that offers good efficiency at acceptable NPSHr. This can be achieved by developing the required head over more than one stage, thus lowering the head per stage to maintain the desired specific speed. Generally a multistage pump is used to develop the required head. Occasionally when service conditions dictate, individual pumps in series are employed.

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5.5

5.6

Reciprocating pumps Reciprocating pumps use pistons, plungers, diaphragms or other devices to displace a given volume of liquid during each stroke of the unit. Reciprocating pumps create and displace their “displacement volumes” by the action of reciprocating element. Plungers, diaphragms etc ar e single acting, i.e., each element can discharge in one direction only. Pistons can be either single or double acting. By their very nature reciprocating pumps produce pulsating flow. A single acting ,simplex pump would produce flow for only ½ of each cycle. By using a multiple number of cylinders to overlap the individual cylinder flows, the pumps’ flow pulsation can be reduced. Pl refer sketch number for reciprocating pump piping Rotary pumps If a single service is desired to define rotary pump usage, it is to pump viscous liquids. A series of fixed or controlled displacement volumes move continuously and at essentially constant speed within the pump. Further movement captures the volume within close clearances and brings it to the discharge region. Rotary pumps use gears , vanes, screws, cams, etc, in a fixed casing to produce positive displacement of a liquid. Following are some of the examples of rotary pumps

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5.7

Selection of pumps Following chart gives an idea of selection of pumps. One of the most important factor of selection of pumps is flow regulation. The energy added by centrifugal pumps varies with through flow, hence their flow regulation is low. ( flow varies widely with system resistance). In reciprocating and rotary pumps the energy depends upon system resistance while the mean flow remains practically constant. Their flow regulation is thus very high. If the service requires high flow regulation , reciprocating /rotary pump is the appropriate choice.

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5.1

6 6.1

Pump piping layout General guidelines Following sketch (sketch-1) shows a portion of a typical plot plan with few Equipments, pipe rack etc shown. For equipment spacing pl refer , plant layout and piping specification number P-GS-PL-003, GE Gap guidelines, and/or OISD 118.

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6.1.1

6.1.2

6.1.3

6.1.4 6.1.5

6.1.6

6.1.7

6.1.8

6.1.9

Pump location will affect the piping routing and supporting. Pumps carrying hydrocarbons and materials above 230 degree C shall not be located below pipe racks, structures, air fin cooers and vessels. Those in non-flamable service may be located beneath the pipe rack without obstructing the access bay, other maintenance requirements of the respective process unit. Pumps shall be located as close to the source of suction in order to minimize pressure drop in the system. The line size and temperature will be the determining factors in piping layout. A preliminary piping layout ( study layout ) shall be made to determine the requirement of spacing between pumps especially in case of side suction/ side discharge, top suction/ top discharge pumps where straight length requirement / platform / CPS requirement etc have to be considered. Reducers in pump suction lines shall be as close as possible to the pump suction/discharge nozzles. Eccentric reducers in pump suction lines shall be flat on top in order to prevent any entrained vapours in the liquid from accumulating in t he high point ( if installed bottom flat ) and thus causing cavitation in the pump. Pumps in boiler feed water service operating close to vapour pressure of the liquid are susceptible to t his type of problems. Reducers in pump discharge should be concentric in most cases. Eccentric reducers may be used in both suction and discharge piping for top suction/ top discharge pumps in order to obtain clearance between suction and discharge piping. Consideration must be given to lube oil and seal oil systems and any cooling water requirements. Care must be exercised not to block access to the pump seals and bearings when routing these lines.. The pump data sheet should always be reviewed to make sure these requirements are not missed. For very large pumps these may be separate on skids. When developing an equipment layout in pump areas, the layout designer must envision potential obstructions around the pumps (e.g. large block valves, steam turbine piping, and tee-type pipe supports from grade). As per Oil Industry Safety Directorate stipulation ( OISD 118 ) 1mtr ( 1000mm ) is the minimum accepted spacing between pumps. Auxiliary piping shall be neatly routed along the base-plate and shall not extend across the operating floor. This piping shall not obstruct inspection covers, bearing caps, upper halves of casings or any other items which require access for operation or maintenance. In order to avoid a fire hazard, lubricating oil, control oil and seal oil pipes shall not be routed in the vicinity of hot process or hot utility pipes .

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6.1.10 Cooling water pipes to pumps and compressors shall not be less than 20NB. Pipes 25NB or less shall have the take-off connection from the top of the header in order to prevent plugging during operation. 6.1.11 When flexibility loops are required between pumps, it is necessary to partially run the lines over the pump and driver. Every effort must be made to minimize maintenance obstructions by running the piping either outside the area directly over the pumps or at a high enough elevation to permit the removal of the pump or driver. 6.1.12 The pump shall be placed in such a manner so that the suction nozzle elevation is always below the vessel/tank nozzle and suction pipe shall be routed so that there is no pockets. 6.1.13 Pumps in vacuum service present special problems. Since the system operates at a negative pressure and very high temperature, the pumps must be located very close to t he suction source. This is often directly below the tower or immediately outside the tower support columns. Pumps located directly beneath the tower can be mounted on a special spring base. 6.1.14 In some rare cases one pump is installed as a common spare between two other pumps in different services. The pump must be manifolded in such a way to accomplish this. 6.1.15 Pumps may be single-stage or multi-stage. Multi stage pumps are usually side suction side discharge. These pumps require significantly more space and faces layout problems. There is usually a straight run requirement (example, 5 pipe diameters) between the suction flange and the first elbow as shown in Sketch no-7. Due to the heavier casing design for high pressures, allowable nozzle loads are often higher for multi-stage pumps making pipe stress problems somewhat easier to resolve. 6.1.16 The location of valves, strainers, spacers/blinds etc. needs special consideration. The option of placing the valves at a higher elevation and providing an operating platform has got its own advantages and disadvantages. If valves are provided at a higher elevation the accessibility for the pumps is enhanced but the operability of the valves becomes difficult. 6.1.17 Some of the Pump Piping layouts generally used are represented in the following pages. It shall be noted that even if the type of pump is same, different piping layouts may be followed. So it is not always necessary that same layout shall be followed for same type of pumps, but is governed by various factors such as temperature, requirement of vertical strainers etc.

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6.2 6.2.1

Centrifugal Pumps. Horizontal centrifugal pumps. These types of pumps are the most commonly used pumps in any industry. Horizontal type pumps are usually of four types: See paragraph no 5.1 a) End suction – top discharge b) Side suction – top discharge c) Side suction - side discharge d) Top suction – top discharge

In this section of the document different types of piping layouts to suit various horizontal centrifugal pumps are being described. 6.2.2 End suction - top discharge pumps Valve hand wheel shall be oriented in such a manner that clear access to the valves and pump is ensured. The suction line valve shall be installed with the stem in the horizontal position, (i.e. install valve in the vertical run of pipe wherever possible). 6.2.3 Special attention must be given to the suction strainer to allow removal for cleaning. The drain connection from the strainer assembly shall have a break flange immediately after the isolation valve and the drain line shall be routed in such a way that the strainer can be removed with ease for maintenance. Sketch no 2& 3 shows an example of suction strainer installation. Strainers shall be located at grade for easy maintenance. 6.2.4 6.2.5 6.2.6 6.2.7 6.2.8 6.2.9

Discharge piping shall be taken to grade for making valves accessible and also for easy supporting. In general, for this type of pumps platform requirements are not necessary for both suction and discharge piping. Care shall be taken while routing discharge line not to block access to couplings. Do not route the suction / discharge piping above the prime mover, otherwise it may create a hindrance while dismantling the prime mover. Small bore piping ( auxiliary piping ) shall be routed in such a manner that tripping hazards are avoided. (pls see sketch no. 13) Some of the examples of end suction – top discharge pump piping are shown in sketches 4,5 & 6.

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SKETCH-2

SKETCH-3 Fixing arrangement of strainer element within a “TEE”

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6.2.10 Top suction – top discharge pumps 6.2.11 To meet straight length requirements, suction valve and strainer need to be placed at a higher elevation and hence requirements of platform shall also be considered for operat ion/ maintenance purpose. Platform struct ure shall not interfere with accessibility / maintainability of pumps. 6.2.12 Platform structure shall be designed in such a manner that it will take care of pipe supports also if required. 6.2.13 Inter distance between pumps may be more due to the requirement of CPSs and/or platform. 6.2.14 Discharge line can be taken to grade for keeping the check valve/ isolation valve in accessible location and also for providing simple supports like trunnion supports etc. 6.2.15 Preliminary piping study layout shall be prepared before finalizing the pump spacing to arrive at an optimum spacing between pumps considering requirement of pipe support structure etc. 6.2.16 Following is an example (sketch no.- 7 ) of top suction – top discharge pump piping

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6.2.17 Side suction – side discharge pumps. Spacing between pumps shall be more due to straight length requirements. This shall be confirmed with the manufacturer. Normally 5 times the diameter of suction pipe size is followed. 6.2.18 Valves and strainer can be placed at accessible location and hence platforms are not required. 6.2.19 Access to coupling shall not be blocked while routing discharge piping so that maintenance requirements are not hampered. 6.2.20 A preliminary piping layout shall be prepared before finalizing pump spacing. 6.2.21 Following are some of the examples ( sketch no.8& 9 ) of side suction – side discharge pumps.

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Vertical centrifugal pump piping . Vertical Centrifugal Pumps may be inline, can (self-contained) or sump pumps. Inline pumps are mounted in the line and supported by the piping. A pedestal is often required for larger in line pumps or where the load is too high for the nozzles to handle. Inline pumps help solve many stress problems usually encountered in hard mounted pumps. The designer must consider access for maintenance and operation in the same way as for horizontal pumps. 6.3.2 Vertical can type pumps are installed in a concrete cylinder but the process fluid is completely contained in the pump can. They are used when there is a high NPSH requirement or at surface condensers servicing large steam turbine driven compressors. This allows the compressor /driver and its associated surface condenser to be mounted at a lower elevation. The same is true for a vessel connected to a vertical can pump. The primary concern for the designer is to provide adequate overhead clearance to remove the pump for maintenance. Allowable nozzle loads for vertical can type pumps are usually higher than for equivalent horizontal centrifugal pumps. 6.3.3 Vertical sump pumps are usually to pump waste products or water from a collection sump/pit. The primary concern is to provide adequate overhead clearance to remove the pump for maintenance. 6.3.4 Some examples of vertical inline/sump pumps piping are included in (sketch no 10 & 11) for better understanding. 6.3 6.3.1

6.4.

Reciprocating pumps piping Reciprocating pumps are used when high head is required. These pumps require a pressure relief valve (PRV) to be installed between the pump and the discharge block valve. The PRV can be external, in the piping, or built-in integrally with the pump casing. Due t o the pulsating action of the reciprocating pumps, the designer must consider space requirements for pulsation dampeners. These are usually furnished with the pump but take up additional more maintenance than other pumps. Do not install any bend (i.e. 90 degree elbow) directly adjacent to the pump discharge. The discharge pulsation dampener must be installed as close to the discharge as possible. Pl refers (sketch no.12 for typical reciprocating pump piping.

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6.5

Rotary pump piping Rotary pumps are required for very heavy or viscous fluids, They deliver a constant pulsation-free flow. Piping for these pumps are very similar to that of centrifugal pumps but is characterised by the absence of block valves in the suction and discharge piping. If block valves are used, a pressure relief valve must be installed between the pump discharge and the block valve. The PRV discharge is usually routed back to the pump suction.

6.6

Cooling tower pump piping. A typical layout is attached in sketch no. 13 for cooling tower pump piping. It is to be noted that the arrangement of pumps are slightly different from that of a layout within unit areas. Tank farm piping. A typical layout is attached in sketch no. 14A & 14B for tank farm pump piping. In the attached sketch top suction- top discharge pump is shown, but other type of pumps also can be used , for e.g. end suction/side suction pumps.

6.7

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7

7.1

7.2 7.3 7.4 7.5

7.6

7.7

Pump piping supports. At the time of piping layout, the type of support, support locations, configuration of support, constructability etc shall be taken care by layout engineer and also ensure that information to Civil Dept. regarding CPSs shall be forwarded in advance. Supports shall be designed strictly according to the restraint conditions in the piping flexibility analysis. First support from pump nozzle shall be adjustable type so that piping can be adjusted with the nozzle concerned while aligning . Trouble free supports which are simple, easy to manufacture and install shall be used . Some of the examples of commonly used pipe supports including shoe support, guide, line stop etc. are attached in sketch no.15A & 15B Discharge piping shall be taken to grade or shall be supported from overhead struct ure. It shall be noted that break flange shall be provided in the first spool from discharge nozzle. This allows piping at the pump to be removed for maintenance. When differential settlement is a problem, the pump suction piping shall be supported from the pump foundation. This can be accomplished by extending the foundation as shown below.

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7.8

7.9 7.10

7.11

The Rests, Guides, Line stops etc shall be judiciously chosen so that after the stress analysis changes are minimized. The addition/relocation of any pipe support on a later stage can alter the basic civil design. Since spring support is very frequently used for high temperature piping provision for the same shall be envisaged during the initial layout itself. The supports shall be located in such a manner so that it should not be a hindrance for the removal of pump parts, accessibility near the pumps or obstruction to personnel movement around the pumps. Preference for simple supports should be always given over other type of supports like struts, which are costly, difficult to install and maintain. Use of a good layout goes a long way in minimizing the use of complex supports.

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8 8.1

8.2

8.3

8.4

8.5 8.6

Auxiliary piping for pumps. Auxiliary piping include pump vent lines, drain lines, seal flush lines, cooling water lines etc. Cooling water is required for cooling mechanical seals, bearings, stuffing boxes etc. Various flushing and cooling schemes are available to combat various environments that are hostile to the mechanical seal face integrity. A mechanical seal has a rotating face and a stationary face. Numerous means such as bellows, wedges, and O- rings are used to seal the rotating face ( seal head ) against the shaft sleeve. In all cases of auxiliary pump piping , the plant layout engineer must carefully review the vendor drawings and P&IDs to ensure that all requirements of cooling have been covered. Some of the seal flush plans (as per API 610) and mechanical seal arrangement are shown below. Sketch no 17A & 17B shows the General arrangement of of an end suction pump showing all nozzles including auxiliary nozzles and seal pot arrangement and seal flush plan.

RECIRCULATION IS FROM A PUMPING RING IN THE SEAL CHAMBER THROUGH A COOLER AND BACK TO THE SEAL CHAMBER.THIS PLAN CAN BE USED ON HOT APPLICATION TO MINIMIZE HEAT LOAD ON THE COOLER BY COOLING ONLY THE SMALL AMOUNT OF LIQUID THAT IS RECIRCULATED (DIAL THERMOMETER (TI) IS OPTIONAL)

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USES AN EXTERNAL RESERVOIR TO PROVIDE BUFFER FLUID FOR OUTER SEAL OF AN UNPRESSURIZED ARRENGEMENT.DURING NORMAL OPERATION CIRCULATION IS MAINTAINED BY INTERNAL PUMPING RING.THE RESERVOIR IS USUALLY CONTINUOUSLY VENTED TO A VAPOUR RECOVER SYSTEM AND IS MAINTAINED AT A PRESSURE LESS THAN THE PRESSURE IN THE SEAL CHAMBER (PRESSURE SWITCH AND HEAT EXCHANGER ARE OPTIONAL)

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9

9.1

9.2

Stress analysis for rotating equipments ( pumps )

External loads imposed by piping on nozzles of rotary equipments shall be less than the specified allowable loads. Examples of rotary equipments are centrifugal pumps, turbines, compressors. If excessive loads are imposed misalignment may result that affects mechanical operation and can cause excessive vibration. A close alignment between rotary and static parts shall be maintained. The provision for expansion of casing and maintaining close clearances requires that the force and moments due to piping are limited. Deformation of casing also may happen due to excessive nozzle loads. Piping connected to centrifugal pumps Considering the coordinate system used as per API 610 , for horizontal pumps, the pump shaft is parallel t o X – axis, Z - axis is in the vertical direction and Y – axis in the transverse direction.Pl see the attached sketches. Allowable forces and moments shall be twice the values as given in the following table as per Jamnagar spec.

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Pump Piping

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