ch06-basic pipe analyisis

8/12/2019 Ch06-Basic Pipe Analyisis

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----- Pipe Analysis-----

Taken From:

Gas Pipeline HydraulicE. Shashi Menon


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WHAT WILL BE DISCUSSED?

Discuss the mechanical strength needed for a pipeline

transporting gas; analyze the impact of pipe diameter, wallthickness, material of construction.


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PIPE WALL THICKNESS (t) Pi (internal pressure) in a pipe causes the pipe wall to be stressed ; if the

stressed > Yield Strength (y) of the pipe material cause permanent/plasticdeformation and ultimate failure. Obviously, pipe should have sufficient strength to

handle the Pisafely.

In addition to Pi, the pipe is also subjected to Pe (external pressure).

Pe (external pressure) :

- the weight of soil above the pipe (buried pipeline);

- Load transmitted by vehicular traffic (pipeline located below roads,

highways, and railroads;

- hydrostatic pressure (offshore pipeline).

In most cases involving buried pipelines transporting gas and other compressible

fluids, the effect of the internal pressure is more than that of external loads.

Therefore, the necessary minimum wall thickness will be dictated by theinternal pressure in a gas pipeline.


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CONTD

tmin (minimum wall thickness)will depend upon thepressure, pipe

diameter, and pipe material. The larger the pressure or diameter, the

larger would be the wall thickness required. Higher strength steel

pipes will require less wall thickness to withstand the given pressure

compared to low-strength materials.

The commonly used formula to determine the wall thickness for

internal pressure is known as Barlows equation.


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BARLOWS EQUATION


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CONTD


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CONTDPada cth. di atas kita menentukan besarnya stress pada dinding pipa akibat internal

gas pressure. Pada cth. Berikutnya kita akan menentukan ketebalan pipa yang

dibutuhkan untuk menahan internal pressure tertentu.

Contoh:

Yield Strength : 52000 psiNPS : 20

Tentukan wall thickness (t) yg dibutuhkanjika internal gas pressure1400 psi, dengan

syarat stress maks. yang dialami pipa adalah 60% dari nilai Yield Strength.

Penyelesaian:

Sh=PD/2t

0,6x52000=(1400x20)/(2xt)

t = 0.4487 in


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THICK-WALLED PIPES


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PIPE MATERIAL AND GRADE


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INTERNAL DESIGN PRESSUREEQUATION

Internal deisgn pressure yang dihitung dari rumus diatas disebutjugaMAOP dari pipeline, atau kadang disingkat MOP.


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-PIPE SEAM JOINT FACTOR (E)

Nilai E bervariasi tergantung dari jenis material danmetode welding yang digunakan (Lihat tabeldibawah)


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CONTD


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-DESIGN FACTORS (F)

CLU(Class Location Unit)


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CONTDCLASS LOCATION


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-TEMPERATURE DERATION FACTORS (T)


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When a pipeline is designed to operate at a certain MOP, it must be

tested to ensure that it is structurally sound and can withstand

safely the internal pressure before being put into service.

Generally, gas pipelines are hydrotested with water by fillingthe test

section of the pipe with water andpumping the pressure up to a

value higher than the MAOPand holdingit at this test pressure for

a period of 4 to 8 hours.

The magnitude of the test pressure is specifiedby design code, and

it is usually 125% of the operating pressure.Thus, a pipeline

designed to operate continuously at 1000 psig will be hydrotested to

a minimum pressure of 1250 psig.

HYDROSTATIC TEST PRESSURE


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CONTD


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CONTD


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CONTD


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ELEVATION PROFILE-HYDROSTATICTESTING


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CONTD


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CONTD


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HYDROTEST BY SUBDIVIDING PIPELINE


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Case Study


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CONTD


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CONTD


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DETERMINING PIPE TONNAGE


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ch06-basic pipe analyisis

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