plant-equipment design - design temp, pressure & flange rating - 20oct14
TRANSCRIPT
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PLANT & EQUIPMENT
DESIGN
DESIGNTEMPERATURE
DESIGNPRESSURE
FLANGERATING
PTC ACADEMY
October 2014
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OBJECTIVES
To establish design temperature, design pressure, criticalexposure temperature (CET), and other parameters that are
necessary for mechanical design of equipment and piping
To determine and select appropriate pipe class to meet design
requirement per appropriate industrial standards
To Understand implication of design temp/pressure as safety
aspects
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Copyright2013
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CONTENTS
Design conditions
Design pressure
Design temperature
Piping flange rating
Case study
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DESIGN CONDITIONS
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DESIGNCONDITIONS
Normal Operation : process pressure and temperature normally inservice (as designed for)
Include Alternate operations e.g. Start up, Shut down, Depressuring,
Fouling condition, Upsets, etc.
Design Conditions
Specifications for equipment and piping including Design
Press, Design Temp, CET, and vessel Pressure Drop
Determining Design Conditions
Most severe sets of Normal and Alternative operating
conditions
Design contingenciesv.s. Remote contingencies
Apply an adjustmentto the identified most severe
conditions to obtained design conditions
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CONTINGENCY
Design Contingency
Abnormal condition including mal-operation, equipment
malfunction, or other event that is not planned
But foreseen that situations are considered in establishing
equipment design conditions
Remote Contingency
Abnormal condition that could result in exceeding Design
Pressure and Design Temperature at
But probability of occurrence is so low that not considered as
a design contingency And/or consideration not mandated by applicable pressure
vessel code, API 5216
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DESIGN PRESSURE
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DESIGNPRESSURES
Design pressures - maximum pressure expected in top of vessel andused to determine minimum wall thickness.
If vessel can operate under vacuum, minimum pressure must also be specified.
Marginsadded to maximum expected pressures to account for
uncertainties in estimating actual pressures Maximum Operating Pressure, PMAX 250 PSIG (17 barg)
PDES= PMAX+ 25 PSIG (1.7 barg)
Maximum Operating pressure, PMAX 250 PSIG (17 barg)
PDES
= PMAX
/ 0.90
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DESIGNPRESSUREGUIDELINES
Maximum Operating Pressure Should Be Determined Based onConsideration of Pressure Variations Due to Changes in:
a. Vapour Pressure
b. Density
c. Feedstock
d. Product Cut Points
e. Static Head
f. Plugging or fouling
g. Pump or Compressor Shutoff Pressure
h. Min expected stream temp
i. Upset conditions
j. Pressure control set point
k. Pumps operating in series
l. Tie in of other process stream
m. External pump flushing oil supply
pressure
n. Friction pressure drop in vessel internal
o. Turbine driven pump/compressor over-
speed
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DESIGNPRESSUREGUIDELINE(CONTINUED)
Max operating pressure of equipment downstream should be specified based
on Pump ShutoffD
P Between Pump Discharge and Downstream Control Valve:
PMAX= Max Suction Pressure + Pump Shutoff DP
From Downstream Control Valve to Last Block Valve:
a. If Closing Valve can Directly Result in Max Suction Pressure:
PMAX= Max Suction Pressure + Pump Shutoff DPb. If Closing Valve does not Directly Result in Max Suction Pressure:
PMAX= Normal Pump Suction Press + Pump Shutoff DP
Max Pump Shutoff:
a) Fix Speed Centrifugal Pumps
Max Pump Shutoff DP = 1.26 x Rated Pump DP
b) Variable Speed Driven Pumps
Max Pump Shutoff DP = 1.39 x Rated Pump DPPage 10
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MAXIMUMALLOWABLEWORKINGPRESSURE(MAWP)
Maximum allowable pressure at top of a vessel or inside equipment atdesignated coincident temperature.
MAWP based on calculations using nominal wall thickness and
exclude corrosion allowance
MAWP assumed to be equal to Design Pressure for cases in which
calculations was not done In final vessel constructions, MAWP can be higher than Design
Pressure due to selection of commercial available plate thickness
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DESIGN TEMPERATURE
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DESIGNTEMPERATURES
Temperatures @ most severe conditionsof coincidentpressure and
temperature
Used for Mechanical Design of equipment
A maximum design temperature, often sets materials of
construction and used to determine allowable stresses
A minimum design temperature, can set materials ofconstruction and toughness requirements, usually specified as
Critical Exposure Temperature (CET)
Sometimes specify two sets of Design conditions, if significantly
different, e.g. Normal and Regeneration of reactor operating conditions
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CRITICALEXPOSURETEMPERATURE(CET)
Lowest temperature at which equipment can be pressurized upto its full design pressure without risk of brittle fracture
Usually occurs during Start up, Shut down, or Depressuring
Important for Refrigerating Systems and Cryogenic Equipment
CET can be determined as lowest metal temperature at either,
whichever is less: Pressure greater than 25% of design pressure, Or
Lowest one-day mean temperature
Maximum safe pressure below the CET determined by
mechanical/ materials engineering specialists
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DESIGNTEMPERATUREGUIDELINES
Determine range of normal operating temperatures and coincidentpressures.
Including normal operations, startup, shutdown, regeneration, steam-out and
other PLANNED scenarios
Add suitable safety margin to account for deviations from normal.
Determine range of temperatures and coincident pressures arising fromabnormal operations, e.g. utility failures, operating failures and other
UNPLANNED scenarios (excluding fire)
No need to add safety margin.
Design temperatures are set by most severe conditionsarising from
normal or abnormal operations.
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DESIGNTEMPERATUREGUIDELINES
(CONTINUED)
Design Temperature higher than 49C Increment of 28C added to the max operating temperature
DT = Max OT + 28 C
If a significant uncertainty exists, larger increment can be added
For Hydrogen service, margin should not be lower than 14C
For high temperature service (> 457C ) consider:Alloy material
Internal insulated (Cold Wall) design
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PIPING FLANGE RATINGS
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PIPINGFLANGERATINGS
Majority of Piping Flanges Manufactured to ASME/ANSI Codes. These
Codes Specify Flange Rating Classes.
Flanges or Piping Components May Be Used at, or Below, Their Pressure
-Temperature Rating (Providing Hydrotest Satisfied)
Classes Up to 600mm Diameter are 150, 300, 400, 600, 900, 1500 and2500 for Carbon Steel and Alloy Flanges
Flanges Now Designated by ANSI Class, Such as Class 150 or 150
ANSI.
Years Ago, Flanges Were Rated in PSIG, and One Still Hears 150 Pound
Flange, or 600 Pound Flange Rating
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SETTINGFLANGERATING
Design pressure generally set at design pressure of connectedequipment
Some flanges may see excursions of temperature and pressure above
design value for a small period of time. Acceptable if the excursions
are less than:
33% for short term events (less than 10 hours per event and less than 100
hours per year).
20% for intermediate events (less than 50 hours per event and less than 500
hours per year).
If temperature, pressure or timing do not meet these requirements, raise theflange rating until the above requirements are met.
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FLANGERATINGSFORCARBONSTEEL
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FLANGERATINGSFOR304SS
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CASE STUDY
Solution here as discussed in class subject to assumption
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CASE STUDY-I
Max. Continuous Operating Pressure = 45.5 barg
Max. Continuous Operating Temperature = 230oC
Short Term Operating Pressure = 66.2 barg
Pipe & Flange are Carbon Steel
1. Determine Flange Rating to Use
2. Max. Pressure to Which the Selected Flange May Be Subjected on a Short-Time
Basis
3. Max. Pressure to Which the Selected Flange May Be Subjected on an
Intermediate-Time Basis
Solution
1. D.T. for Uninsulated Flange = 230oC
For Design Pressure = 45.5 barg
From Table, Flange Rating = Class 600
2. From Table, Maximum Pressure for Class 600 Flanges = 83.9 barg
On Short-Time Basis, Can Overpressure Piping Flanges by 33% = (83.9)(1.33) = 111.6 barg
3. On Intermediate-Time Basis, Can Overpressure Piping Flanges by 20% = (83.9)(1.2) = 100.7 barg
and consideration. It may not be absolutely correct.
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CASE STUDY-I (SUGGESTEDSOLUTION)
Max. Continuous Operating Pressure = 45.5 barg
Max. Continuous Operating Temperature = 230oC
Short Term Operating Pressure = 66.2 barg
Pipe & Flange are Carbon Steel
1. Determine Flange Rating to Use
2. Max. Pressure to Which the Selected Flange May Be Subjected on a Short-Time
Basis
3. Max. Pressure to Which the Selected Flange May Be Subjected on an
Intermediate-Time Basis
Solution
1. Design Temperature = 230 + 28oC = 258oC
Design Pressure = 45.5/0.9 = 50.5 barg
From Table Select temperature @ 300oC to cover design temperatureFlange Rating = Class 600 to have
pressure covering design pressure (max pressure = 79.6 barg at 300oC)
2. On Short-Time Basis, Can Overpressure Piping Flanges by 33% = (79.6)(1.33) = 105.9 barg
3. On Intermediate-Time Basis, Can Overpressure Piping Flanges by 20% = (79.6)(1.2) = 95.5 barg
Flange rating of class 600 can well cover short term operating pressure of 66.2 barg
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CASE STUDY - II
Max. Pump Discharge Press = ?
Design Pressure of Exch. A = ?
Design Pressure of Exch. B = ?
Piping Class ?
Design Temperature of Exch. A = ?
Design Temperature of Exch. B = ?
1.38 barg Normal
6.90 barg Max.
41.38 barg Normal
232oC Normal
40.69 barg Normal
149oC Normal
Pump DP =40barHeat EX-A Heat EX-B
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CASE STUDY - II
Max. Pump Discharge Press = 1.38 + 40 = 41.38 barg ?
Design Pressure of Exch. A = 41.38/0.9 = 45.98 barg ?
Design Pressure of Exch. B = 41.38/0.9 = 45.98 barg ?
Piping Class
Class 600 Flanges for CS PipingDesign Temperature of Exch. A = 232 + 28 = 260oC ?
Design Temperature of Exch. B = 232oC ?
1.38 barg Normal
6.90 barg Max.
41.38 barg Normal
232oC Normal
40.69 barg Normal
149oC Normal
Pump DP =40barHeat EX-A Heat EX-B
Solution here as discussed in class subject to assumption
and consideration. It may not be absolutely correct.
CASE STUDY II (SUGGESTED SOLUTION)
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CASE STUDY II (SUGGESTEDSOLUTION)
Pressureassuming pump DP = rated pump DP and fixed speed centrifugal pump
Max pump shut-off DP = 1.26 x 40 bar = 50.4 bar
Max. Pump Discharge Press, PMAX= 6.9 + 50.4 = 57.3 barg
Design Pressure of Exch. A = PMAX/0.9 = 57.3/0.9 = 63.7 barg
Design Pressure of Exch. B = 63.7 barg, Heat EX-B also subject to same PMAXof pump once outlet block-valve is closed
Temperatureassuming 232oC = max operating temperature
Design temperature of system = 232 + 28 =260oC
Piping Class
Class 600 Flanges for CS Piping @ 300oC and 79.6 barg to cover 63.7 barg design pressure @ 232oC designtemperature
Design Temperature of Exch. A = 260oC
Design Temperature of Exch. B = 260oC, assuming Heat EX-B and Heat EX-A can be operated independently. Therefore, Heat
EX-B can also see the same inlet temperature as Heat EX-A.
1.38 barg Normal
6.90 barg Max.
41.38 barg Normal
232oC Normal
40.69 barg Normal
149oC Normal
Pump DP =40barHeat EX-A Heat EX-B
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Q&A