Process Plant Piping Design

8/9/2019 Process Plant Piping Design

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A piping system conveys fluid from onelocation to another. Within a process

plant, the locations are typically one or

more equipment items (e.g., pumps,

pressure vessels, heat exchangers,

process heaters, etc.), or individual process plants that are within the

boundary of a process facility .



A piping system consists of: Pipe sections

Fittings (e.g., elbows, reducers, branch

connections, etc.) Flanges, gaskets, and bolting

Valves

Pipe supports and restraints

Each individual component plus the overall

system must be designed for the specified design

conditions.





Nominal pipe size (NPS) is a dimensionless designator of pipe size. It indicates standard

pipe size when followed by the specific size designation number without an inch symbol.

For example, NPS 2 indicates a pipe whose outside diameter is 2.375 in. The NPS 12 and

smaller pipe has outside diameter greater than the size designator (say, 2, 4, 6, . . .).

However, the outside diameter of NPS 14 and larger pipe is the same as the size

designator in inches.

For example, NPS 14 pipe has an outside diameter equal to 14 in. The inside diameter

will depend upon the pipe wall thickness specified by the schedule number

Diameter nominal (DN) is also a dimensionless designator of pipe size in the metric unit

system, developed by the International Standards Organization (ISO).



PIPE SCHEDULE :

S

PSN

1000=

SN = Schedule Number

P = Service Pressure (psi)

S = Allowable Fiber Stress (psi)

Std (Standard) ; S (STRONG ; XS (extra strong)



A106 Grade B Carbon Steel Pipes - Pressure and Temperature Ratings

Pressure (psig) and temperature (deg F) ratings of A106 Grade B carbon steel pipes -

temperatures ranging 100 oF - 750 oF

http://www.engineeringtoolbox.com/a106-carbon-steel-pipes-d_370.html







The accepted formula is Schedule Number = 1,000 x (P/S)

where,P = internal pressure, pounds-per-square-inch-gauge (psig),

S = allowable fiber stress (ultimate tensile strength of the steel in

psi).

Rearrange terms to solve for P, assuming schedule number and Sare known. Therefore P = Schedule number x S/1,000

Calculate internal pressure (P) based on Schedule 40 steel pipe,

and an allowable fiber stress (S) value of 60,000-psi (ultimate

tensile strength for A106 Grade B Carbon Steel Pipe).

Therefore, P = 40 x 60,000/1,000 = 2,400-psi .

This is reasonable, based on a current-day published value of

2,847-psi for 1-inch Schedule 40 steel pipe (with the range

temperature 1000F – 7500F).



B31.1 - Power Piping

B31.2 - Fuel Gas Piping

B31.3 - Process Piping

B31.4 - Pipeline Transportation Systems for Liquid Hydrocarbons and Other

Liquids

B31.5 - Refrigeration Piping and Heat Transfer Components

B31.8 - Gas Transmission and Distribution Piping Systems

B31.8S - Managing System Integrity of Gas Pipelines

B31.9 - Building Services Piping

B31.11 - Slurry Transportation Piping Systems

B31G - Manual for Determining Remaining Strength of Corroded Pipelines



Terminologi yang digunakan pada material yang

digunakan pada pipa maupun sistem perpipaan.



PIPING MATERIALS (GRADE)

UTS : Ultimate Tensile Strength YS : Yields Strength



A106 Grade B Carbon Steel Pipes

(Pressure-Temperature Rating)

1) STD (standard)

= schedule 40

2) XS (extra strong)

= schedule 80



PIPING STANDARDS (CLASS)



Provides requirements for:

• Design• Materials

• Fabrication

• Erection• Inspection

• Testing



Piping and piping components, all fluid services:

Raw, intermediate, and finished chemicals

Petroleum products

Gas, steam, air, and water

Fluidized solids

Refrigerants

Cryogenic fluids Interconnections within packaged equipment



Piping systems for internal gauge pressures at or above zerobut less than 15 psi, provided that the fluid is nonflammable,

nontoxic, and not damaging to human tissue, and its design

temperature is from -20°F through 366°F.

Power boilers that are designed in accordance with the ASMEBoiler and Pressure Vessel Code Section I and external boiler

piping that must conform to ASME B31.1.

Tubes, tube headers, crossovers, and manifolds that are

located inside a fired heater enclosure.

Pressure vessels, heat exchangers, pumps, compressors, and

other fluid-handling or processing equipment. This includes

both internal piping and connections for external piping.



General

Normal operating conditions

Design conditions

Design pressure and temperature Identify connected equipment and

associated design conditions

Consider contingent conditions

Consider flow direction

Verify conditions with process engineer



σl = Axial or Longitudinal Stress

σc = Circumferential (Hoop) Stress

σr = Radial Stress

t = Wall Thickness

P = Internal Pressure



The stress in circumferential direction at a point in the tube or

cylinder wall can be expressed as:

σ c = [(pi r i 2 - po r o

2 ) / (r o2 - r i

2 )] - [r i 2 r o

2 (po - pi ) / r 2 (r o2 - r i

2 )]

Where,

σ c = stress in circumferential direction (MPa, psi)

pi = internal pressure in the tube or cylinder (MPa, psi)

po = external pressure in the tube or cylinder (MPa, psi)

r i = internal radius of tube or cylinder (mm, in)

r o = external radius of tube or cylinder (mm, in)

r = radius to point in tube or cylinder wall (mm, in)maximum stress when r = r i (inside pipe or cylinder)

t = wall tube thickness = r 0 - r i

σ c < Maximum Allowable Stress of Pipe Materials



Function of : Material properties

Temperature

Safety factors

Established to avoid: General collapse or excessive distortion

from sustained loads

Localized fatigue failure from thermalexpansion load

Collapse or distortion from occasional loads



A piping system must be modified to add a new, spare

heat exchanger. You have been assigned the responsibility

to determine the required wall thickness for the pipe

from the heat exchanger to several pumps.

The piping system will have a design temperature of650°F .

The design pressure is 1,380 psig.

The pipe outside diameter is 14 in.

The material is ASTM A335, Gr. P11 (1¼ Cr – ½ Mo),Seamless Ferritic Alloy-Steel Pipe for High-Temperature

Service.

Corrosion allowance is 0.0625 in.

R i d W ll Thi k f I t l P f St i ht Pi



t = Required thickness for internal pressure, in.

P = Internal design pressure, psig

S = Allowable stress in tension (Table A-1), psi E = Longitudinal-joint quality factor (Table A-1B)

Y = Wall thickness correction factor (Table 304.1.1)

Required Wall Thickness for Internal Pressure of Straight Pipe

(ASME B31.3)

Corrosion allowance (CA) is an additional thickness that is added to account for

wall thinning and wear that can occur in service. The corrosion allowance is

based on experience and data for the particular pipe material and fluid service.tm = Total minimum required wall thickness, in

Mill tolerance accounts for the difference between the actual manufactured pipe

wall thickness and the “nominal” wall thickness specified in the relevant pipe

dimensional standard. The typical pipe mill tolerance is 12.5%. This means that the as-supplied pipe wall thickness can be up to 12.5% thinner than the nominal

thickness and still meet its specification requirements. Use the following

equation to determine the minimum required nominal thickness to order.

t nom = Minimum required nominal pipe

wall thickness, in.



Source : ASME B31.3 (Table A-1) Basic Allowable Stress in Tension for Metal

Source : ASME B31.3 (Table A-1B) Basic Quality Factor for Longitudinal Weld Joint







Pipe flanges that are made to standards called out

by ASME B16.5 or ASME B16.47 are typically madefrom forged materials and have machined surfaces.

ASME B16.5 refers to nominal pipe sizes (NPS) from

½" to 24“ and ASME B16.47 covers NPSs from 26"

to 60".

Each specification further delineates flanges into

pressure classes: 150, 300, 400, 600, 900, 1500 and

2500 for ASME B16.5; and ASME B16.47 delineatesits flanges into pressure classes 75, 150, 300, 400,

600, 900 . Flange strength increases with class

number.

http://en.wikipedia.org/wiki/Nominal_pipe_size

http://en.wikipedia.org/wiki/Nominal_pipe_size







Materials for flanges are usually under ASMEdesignation:

• SA-105 (Specification for Carbon Steel Forgings

for Piping Applications),• SA-266 (Specification for Carbon Steel Forgings

for Pressure Vessel Components),

• SA-182 (Specification for Forged or Rolled

Alloy-Steel Pipe Flanges, Forged Fittings, and

Valves and Parts for High-Temperature

Service).







New piping system to be installed at existing plant.

Determine required flange class.

• Pipe Material : 1 ¼ Cr - ½ Mo

• Design Temperature : 700°F• Design Pressure : 500 psig

• Determine Material Group Number (Table 1)

→ Group Number = 1.9

• Find allowable design pressure at intersection of design

temperature and Group No. Check Class 150 . (Table 2)

Allowable pressure = 110 psig < design pressure

Move to next higher class and repeat steps

• For Class 300, allowable pressure = 570 psig• Required flange Class: 300

















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Process Plant Piping Design

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