Process Plant Piping Design

A piping system conveys fluid from one

location 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

PIPE SCHEDULE :

S

P

SN

=

1000

SN = Schedule Number

P = Service Pressure (psi)

S = Allowable Fiber Stress (psi)

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 o_{F - 750} o_F

 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 S are 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

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

Terminologi yang digunakan pada material yang

digunakan pada pipa maupun sistem perpipaan.

PIPING MATERIALS (GRADE)

A106 Grade B Carbon Steel Pipes

(Pressure-Temperature Rating)

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

 Piping systems for internal gauge pressures at or above zero

but 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 ASME

Boiler 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

σ

σ

σ

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 = [(p_i r_i2 _{- p}

o ro2) / (ro2 - ri2)] - [ri2 ro2 (po - pi) / r2 (ro2 - ri2)]

Where,

σ_c = stress in circumferential direction (MPa, psi)

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

p_o = 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 = r0 - ri

Function of :

 Material properties

 Temperature

 Safety factors

Established to avoid:

 General collapse or excessive distortion

from sustained loads

 Localized

fatigue

failure

from

thermal

expansion load

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 of

650°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.

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

Design pressure (P) = 1,380 psig. Pipe Outside Dia. (D) = 14 in.

For the A335, Gr. P 11 material:

S = 16,150 psi. [Table A-1 of ASME B31.3 at 650°F] E = 1.0 [Table A-1B of ASME B31.3]

Y = 0.4 [Table 304.1.1 of ASME B31.3], since the

material is ferritic and the temperature is below 900o_F.

Based on the given information: The following equation applies:

In this case, a 0.0625 in. corrosion allowance has been specified.

t_m = t + c = 0.577 + 0.0625 t_m = 0.6395 in.

 Pipe flanges that are made to standards called out

by ASME B16.5 or ASME B16.47 are typically made

from 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 delineates

its flanges into pressure classes 75, 150, 300, 400,

600, 900. Flange strength increases with class

Materials for flanges are usually under ASME

designation:

•

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

•

→

•

 Allowable pressure = 110 psig < design pressure  Move to next higher class and repeat steps

•