Tekna
Offshore Pumps 2007
Pump Theory API Reciprocating
Displacement Pumps.
Steve Digby
SPX Process Equipment Limited
Bran+Luebbe Operation U.K.
SPX Process Equipment
2003
WCB-Flow Products
2002
GD Engineering
2005 Plan
Employees 2585
OFM
Oilfield Fabricating & Machine
After Market & Field Services
Pump Theory
API Reciprocating Displacement Pumps
Topics
•
•
•
•
•
Reciprocating versus Rotary Pumps
Basic Operation of Reciprocating Pumps
API Specifications 674 & 675
Suction Side Installation Considerations
Overall Cost of Ownership
Pump Theory
API Reciprocating Displacement Pumps
• API stands for American Petroleum Institute
• API 674 and 675 are widely used as an industrial
standard for reciprocating displacement pumps.
• Mainly used in Petroleum, Chemical Processing, and
Oil&Gas Industry.
• Describes and specifies constructional design,
qualification criteria, and how pumps and documentation
shall be executed.
Pump Theory
API Reciprocating Displacement Pumps
Reciprocating metering/dosing pumps deliver a
controlled & accurate flow to predetermined points of a
process independent of pressure.
Pump Theory
API Reciprocating Displacement Pumps
API 675 Metering Pump With
Diaphragm Pumphead
API 674 Reciprocating Triplex
Pump With Diaphragm
Pumpheads
Pump Theory
API Reciprocating Displacement Pumps
Metering Pump Equation
V=A.h.n
V = theoretical Volumetric flow of the
metering pump
A = plunger square area
h = stroke length
n = stroking speed (stroke frequency)
Positive Displacement Pumps
Reciprocating
Definition (in accordance with API Standard 674)
There is no actual definition in the standard other than
highlighting the difference between a Power Pump & Direct
Acting Pump.
Essentially these pumps transmit a predetermined mass
flow at medium to high pressure.
Pumps are normally configured in Triplex, Quintuplex and
Septuplex designs.
Positive Displacement Pumps
Controlled Volume
Definition (in accordance with API Standard 675)
“A controlled volume pump is a reciprocating pump in
which precise volume control is provided by varying
effective stroke length”.
• Such pumps are also known as metering, proportioning,
chemical injection, dosing, or controlled volume pump.
• These pumps deliver a controlled & accurate flow to
predetermined points of a process independent of
pressure.
Pump Theory
API Reciprocating Displacement Pumps
Typical Deviations to API 675
API Listing
1.5 Equipment offered is referring to German and European standards i.e. DIN, EN, IEC,
ISO,....
2.2.5.1 Details of threading conform to ISO.
2.12.3 Unless proposed differently visual indication of capacity setting is shown as actual stroke
length.
2.13.1.13 Bolts are calculated and selected in accordance with German pressure vessel code
(AD-Merkblätter).
3.1.7 Motors are flanged directly to the pump. Consequently, there is no need for jackscrews.
3.3 Metering pumps are suitable for mounting directly onto prepared concrete. Base plates are
therefore optional and can be quoted at additional cost.
3.3.9 If not stated differently base plates will not be furnished with jackscrews.
3.4.3.2 If not stated differently single point terminal box for instrumentation is not included.
3.4.4.3 The gauges used for local diaphragm rupture indication have dials either 63 mm or 100
mm, depending on size of pumphead.
3.4.5 Electrical systems are not included unless expressly required and specifically quoted.
Pump Theory
API Reciprocating Displacement Pumps
API Data Sheet – Purchaser Information
1
2
3
4
5
6
7
For:
No. of motors required 1
Site
Serial no.
TBA
Remarks
Notes: O indicates information to be completed by Purchaser. indicates information to be completed by manufacturer.
API standard 674 governs unless otherwise noted
OPERATING CONDITIONS (to be completed by purchaser)
8
9
10
11
12
13
14
15
Liquid
(HC) Condensate
Pumping temperature (°C) PT:
Normal 19 Maximum 58Minimum -9
Density @ PT (kg/m³): 569,8
Vapor pressure @ PT (bar):
Viscosity @ PT (cP): 0,16
Acceleration head (m) Note 1
NPSH available (m): 14,7
Capacity @ PT (m³/h):
Maximum Note 2
Minimum Note
Rated
3 5,3
Discharge pressure (bar g):
Maximum
Minimum Rated Note 4
Suction pressure ( bar g):
Maximum
Minimum Rated 17,8
Differential pressure (bar g):
Maximum 19,2
Minimum Rated 16,2
Pump Theory
API Reciprocating Displacement Pumps
Installation Considerations & How to Avoid Problems
Pump Theory
API Reciprocating Displacement Pumps
Flow Pattern of various Pumps Types
Simplex Pump
Duplex Pump
Triplex Pump
Centrifugal Pump
Pump Theory
API Reciprocating Displacement Pumps
What we are Trying to Avoid
Suction Side
• Insufficent NPSHA
• Pump Starvation
• Cavitation
Discharge Side
• Insufficent Flow
• Over Pressure
• Pipe Hammer
General Poor Pump Operation
In almost all cases of insufficient flow rate or frequent service
calls the pump will be blamed, not the system
Only Recognised as Problems During Commissioning or
Initial Operation.
Pump Theory
API Reciprocating Displacement Pumps
Many Installations Are Designed On Smooth Flow
Conditions & Ignore Factors Such as:• Reciprocating Pumps Generate a Pulsating
Flow
• ~3x Equivalent Smooth Flow.
• Line Losses Can be High.
• Crucial on Critical Applications i.e. Liquid
Gases, High Temperature, Volatile Liquids.
Pump Theory
API Reciprocating Displacement Pumps
Flow Pattern of a Single Head Pump
100 % Capacity setting
60 % Capacity setting
Discharge
Top
dead
Center
Suction
Bottom
dead
Center
Bottom
dead
Center
Pump Theory
API Reciprocating Displacement Pumps
Two Major Factors That Can Adversely Affect The
Operation of Reciprocating Pumps Buy Are Often
Overlooked are:
•Friction Losses
Higher Viscosity Applications
Pressure Required to ensure that the liquid flows continually in the
system during the maximum demanded flow volume.
Low Viscosity Application
•Mass Acceleration Losses
Pressure Required to cause the liquid to move at the beginning of
each plunger stroke
•Both Have a high impact on NPSHA .
•Only the higher of the two values is considered.
•On reciprocating pumps this is generally Mass Acceleration.
Pump Theory
API Reciprocating Displacement Pumps
Factors Affecting Mass Acceleration Pressure
• Plunger or Piston Diameter.
• Stroke Length
• Internal Pipe Diameter & Overall Length.
• Pump Speed.
• Pump Configuration (Single or Multi Head)
Example.
Single Head Pump 20mm Dia Plunger x 20 mm Stroke Length
Operating Speed 100 Strokes/Min Fitted To 8mm NB Pipe
Mass Acceleration Pressure = 0.84 m/m
Pipe Length = 10m
∆P = 8.4m or 0.84 Bar
Pump Theory
API Reciprocating Displacement Pumps
Net Positive Suction Head
Net positive suction head (NSPH) is the total inlet
pressure, stated in meters head minus the vapor
pressure of the liquid in meters
Pump Theory
API Reciprocating Displacement Pumps
What is a System ?
(in terms of the issue “NPSH”)
Suction
vessel
p(abs)
or Habs
A system is normally composed of:
• a pump
• a vessel from which the pump takes the liquid (suction vessel)
• piping between pump and suction vessel including valves,
elbows, strainers, etc.
L
(Length of suction piping)
Pump
Hst
(Static
head)
d
(pipe inside diameter)
Pump Theory
API Reciprocating Displacement Pumps
Mass Acceleration Forces
Simplex Pump
Duplex Pump
Triplex Pump
Centrifugal Pump
Pump Theory
API Reciprocating Displacement Pumps
Net Positive Suction Head Available
NPSHA is a property of the system & determined
by the purchaser!
Net Positive Suction Head Required
NPSHR is a property of the pump and is the minimum
pressure required, measured at the suction flange, to
prevent cavitation.
For satisfactory pump operation NPSHA should always
exceed NPSHR by a minimum of *1 -2 m
*(varies for different pump types and suppliers)
Pump Theory
API Reciprocating Displacement Pumps
Total head
The NPSH concept
Head of
vapor
pressure
Head of
friction
losses
Head in
suction vessel
(above liquid
level)
Head of
mass
acceleration
losses
NPSHA
Static
head
NPSHR
NPSH margin
Pump Theory
API Reciprocating Displacement Pumps
How can NPSHA be calculated ?
The calculation is no more than determining the
difference between
• positive heads
i.e. absolute head in suction vessel plus static head
and
• negative heads (losses)
i.e. head due to vapor pressure, friction and mass
acceleration
NPSHA = H +Hst - Hvp - ΣHfr - Hma
Pump Theory
API Reciprocating Displacement Pumps
Inadequate NPSHA Will Cause Cavitation Leading To:
• Erratic Performance
• Reduced Flow
• Erosion in The Plunger Packing Area and Non Return
Valves
• A Lot of Noise!!!
• Cost
Non Return Valves
Plunger Sealings
Pump Theory
API Reciprocating Displacement Pumps
Considerations to Maximise The NPSHA of the System
• Minimise the pipe length
• Maximise the bore diameter
• Minimise no of bend, tees and valves etc.
• Use of Pulsation Dampening Devices
• Increase Pressure (Booster Pump, Nitrogen
Blanket, Static Head etc).
• Use of a multi head pump.
• Adequate Pipe Supporting
Pump Theory
API Reciprocating Displacement Pumps
Pulsation Dampeners
Pump Theory
API Reciprocating Displacement Pumps
Pulsation Dampener Affect
0
180
360
Pump Theory
API Reciprocating Displacement Pumps
Overall Cost of Ownership
Comparison of the investment and maintenance costs of a hydraulically
actuated diaphragm pump compared to a packed plunger pump
Process Fluid
Flowrate
Process Pressure
Operating Hours
: Methanol
: 12m3/hr
: 160 bar
: 8000/year
Diaphragm Pump
Packed Plunger Pump
Pump Type
Triplex
Triplex
Investment Cost
250,000
150,000
Annual Spare Use
- plungers
None
6 x 3,000 = 18,000
- plunger packing
3 x 500 = 1,500
12 x 1,000 = 12,000
- diaphragms
3 x 1,000 = 3,000
None
- pump valves
6 x 2,000 =12,000
6 x 2,000 = 12,000
- labour costs
10 h x 150 = 1,500
50 h x 150 = 7,500
18,000
40,500
Maintenance costs after
3 years operation
63,000
Inc 1 set of plungers
148,500
Total costs after 3 years
operation
313,000
298,500
Annual maintenance
costs
Comments
Energy costs
Lubrication of Plunger
Packing Leakage
~5% Lower
Not Required
None
Packing Friction
Necessary
Needs to be contained
Pump Theory
API Reciprocating Displacement Pumps
Thank you - Questions