Design & Construction of Piping Systems

Design & Construction of Piping Systems

Prepared by Eng. Mostafa A. El-Sayed

Aim of Seminar To know piping design basics by going through the following points:       

Design of pressure components. Pipe Span calculations. Design of pipe supports & hangers. Stiffness & flexibility. Expansion & stresses. Line expansion & flexibility. Supports & anchorage of piping.

Design of pressure piping 

Many decisions need be made in the design phase to achieve this successful operation, including: -

Required process fluid quantity. Optimum pressure-temperature. Piping material selection. Insulation selection (tracing). Stress & nozzle load determination. Pipe support standard.

The codes provide minimal assistance with any of these decisions as the codes are not design manuals.

Design of pressure components 

Pipe Structure “static” design, not Layout design.

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Limitations: Code, Pressure, Temperature, How long is the plant lifetime, What is the plant reliability, etc..

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Piping designed according to B31.3 has less lifetime than B31.1 due to lower F.S.

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Reliability of piping under B31.1 should be higher than B31.3

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Given that the code is a product of pressure technology, one of the concerns is the pressure-temperature ratings of the components.

Design of pressure components 

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Each system be it vessel or piping has some base pressuretemperature rating. This is essentially the pressure temperature rating of the weakest member of the system. This can be translated that no minor component (valve, flange, etc) shall be the weakest link. The key components of the design conditions are the design pressure and the design temperature. Design pressure is defined as the most severe sustained pressure which results in the greatest component thickness and the highest component pressure rating. Design temperature is defined as the sustained pipe metal temperature representing the most severe conditions of coincident pressure and temperature.

Design of pressure components 

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Thus we can try to simplify our stresses into two main categories; Pressure stress is the circumferential stress (primary stress) or hoop stress, which is known to be not self limiting. Temperature stress is the shear or bending stress (Secondary stress), known to be self limiting. In addition VIBRATION, has to be addressed as low cycle high stress named as “thermal expansion cycles”, represented by f=1 for 7000 cycles, otherwise detailed design has to be performed to prove that the pipe will withstand high cycle, low stress loads.

Design of pressure components Wall Thickness Calculation 

The code assists the designer in determining adequate pipe wall thickness for a given material and design conditions as follows: - Calculate the pressure design thickness “t” - Add the mechanical corrosion and erosion allowances “c” to obtain the thickness tm=t+c - Add mill tolerance (MT) to tm, then select the next commercially available wall thickness. - Provided t