plant-equipment design - design temp, pressure & flange rating - 20oct14

7/23/2019 Plant-Equipment Design - Design Temp, Pressure & Flange Rating - 20Oct14

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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

2

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


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



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Q&A

plant-equipment design - design temp, pressure & flange rating - 20oct14

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