Wednesday, May 18, 2011


Ini adalah beberapa pertanyaan dan jawaban mengenai pipe stress analysis dan mudah-mudahan bisa menjadi ilmu tambahan buat rekan-rekan semua tapi semua dalam bahasa Inggris dan mohon infonya juga mengenai peluang kerja untuk saya sebagai design engineer (Piping).

I. Whast is the objective of stress analysis ?
  The answers are :
A. To ensure that the stresses in piping componenrs in the system are within allowable limits.
B. To solve dynamic problems developed due to mechanical vibration, fluid hammer , pulsation, relief valve etc
C. To solve problems associated due to higher or lower operating temperature as :
1. Displacement stress range
2. Nozzle loading on connected equipment
3. Pipe displacements
4. Loads & moments on supporting structure.

II. What are steps involved in stress analysis (or any stress package carried out) ?
The Answers are :
1. Identify the potential loads that the piping system would uncounter during .the life of the plant
2. Relate each of these loads to .the stresses and strains developed.
3. Get .the cumulative effect of the potential loads in the system.
4. Decide the allowanbe limits the system can withstand without failure as per code
5. After the system is designed to ensure that the stresses are within safe limits.

III. How are the steps involved in stress analysis package?
The Answers are :
1. Sustained Loads : Those due to forces present during normal operation
2. Occasional Loads : Those present during rare intervals of operation
3. Dispacement Loads : Those due to displacement of pipe. (self limiting stresses due to thermal effects)

IV.  What are the sources of sustained load generated in piping system ?
The anwers are :
1. Internal fluid pressure
2. Dead weight of Pipe with fuid and its attachments
Sustained load is calculated as :
Weight of Pipe with Fluid + internal fluid pressure load + Load due to springs (W+P1)

V. What are the inputs required for stress analysis of a piping systems?
The answaers are :
1. Pipe size
2. Fluid Temperature
3. Pipe Material
4. Model
5. Design Pressure
6. Insulation Thickness
7. Specific Gravity
8. Friction Coefficient

VI. What is the sample of occasional load?
The Anwers is
1. Wind Load
2. Seismic load
3. Forces due to relief or blow down
4. Pressure wave generated due to water hammer effects.

VII. What is the desired life cycle for piping in  operation?
The anwers is :
Desired life cycle for piping in operation is 20 years (7000 cycles)
The normal number of cycles for which the dispacement or thermal stresses are designed is 7000 cycles.

VIII. What Do you means by Stress Intensity Factor (SIF)?
The answer is
Stress Intensity Factor (SIF) is the ratio of maximum stress intensity to normal stress. It is used as safe factor to account for the effect of localised stress on piping under respective loading. In piping it is applied to welds, fittings, branch connections etc where stress concentration and possible fatique failure may accur.
Example : SIF for Reducer and Weld Neck Flange is 1.0
                SIF for socket weld flange is 1.3

IX. How much should be the pressure for Hydro-Test ?
The Answers are :
Hydrotest pressure should be calculated as follow except as provided agaist point no. D
A. 1.5 times design pressure
B. For design temperature above the test temperature , minimum test pressure can be calculated as :

         Pt  = (1.5 x P x St )/S

Where: Pt = Minimum Test Pressure
            P  = Internal Design Pressure
            St = Allowance Stress at test temperature
            S   = Allowance Stress at design temperature

C. If a test pressure as per above would produce a stress in excess of the yeild strength at test temperature may be reduced to maximum pressure that will not exceed the yeild strength at test temperature.
D. If the stress pressure of piping exceeds the vessel pressure and it is not considered practicable to isolate piping from vessel, the piping and vessel may be tested together at test pressure of the vessel when approved by owner and provided the test pressure for vessel is not lessthan 115%  of piping design pressure adjusted for temperature as per point no. B.

Itulah tadi sembilan pertanyaan mengenai piping stress analysis dan nanti akan saya tambah lagi minggu depan mengenai stress piping ini dimana saya pun lagi stress karena bakal kehilangan pekerjaan karena project berakhir.

Kerteh, 18 Mei 2011 jam 19.53

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