A Brief Introduction into Piping Loads

Every Engineering Design meant to operate its lifetime successfully without/fewer breakdowns.This is possible only by successfully forecasting the kind of loads it's going to expose during its course of operation.While designing a Piping System we have to consider a minimum, the following Loads  

I) Design Pressure

The Design Pressure of Each component in a piping system shall not be less than the pressure at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service. The most severe condition is that which results in the greatest required component thickness and the highest component rating.

Usually, the following basis is adopted for arriving at design pressure

a)  Design Pressure of the connecting equipment

b)  Set pressure of the pressure relief valve connected for the safety of the system

c)  Discharge pressure of the Pump in the System

d)  All systems operating below atmospheric pressure shall be designed for full vacuum

e)Piping systems leaving the process area shall be designed for a closed valve outside the process area. If this cause an increase in flange rating for the piping outside the process area an acceptable alternative is to lock open all the block valves between the last block valve in the process area and the downstream pressure relief.

f)  When a line connected with pipe or Equipment of higher rating, the line shall be rated the higher rating.(Material should also be of the higher rating )

Effects Of Temperature And Wind on PipingCredit: Bentley

II) Design Temperature

 Design temperature of each component in a piping system is the temperature at which, under the coincidence pressure, the greatest thickness or highest component rating is required.

 For unInsulated metallic components, this depending upon the fluid temperature, the component Design temperature can be considered 90-95% of the Fluid temperature it is allowing to pass through

 For ExterInsulatedulated Piping, the Component Design Temperature shall be the Fluid Temperature. Cases where Piping is heated or cooled by external jacketing, this effect shall be considered in establishing the Component Design temperature.

Usually, the Design Pressure and Temperature are given by the Process Department in the Form of the Fluid list at the initial stage of the Project and as a Line List on advanced stage.

 Apart from the Pressure and Temperature condition, following Loads are also acted on Piping System.

III)Ambient effects 

Cooling Effects on pressure-The cooling of a gas or vapor in a piping system may reduce the pressure sufficiently to create an internal vacuum. Provisions should be there for withstanding the External pressure or to break the vacuum.

IV) Fluid expansion effects

 Care should be given for the expansion of Static Fluid in a component while heating of the same, measures for relieving or withstand pressure should be incorporated in the system.

V)Atmospheric icing

Locations where Design Minimum temperature of a piping below 0^o  C, the possibility of moisture condensation and build-up of ice shall be considered and provisions to avoid resultant malfunctions   of components

VI) Dynamic Effects

Impact forces by external or internal conditions such as flow rate change, hydraulic shock, liquid or fluid slugging Flashing and geysering

VII) Wind:

Load due to the Exposed wind and this will vary according to the geographic location of the plant,  area where the pipe is located(Indoor, outdoor), Elevation and Pipe size etc.

VIII) Earthquake

Earthquake-induced horizontal forces are a major concern, Especially Plants at Earthquake prone areas.

IX) Vibration

Arise Due to Impact, Pressure Pulsation, resonance, compressors and Wind Loads

X) Discharge Reactions

Let down or Discharge of Fluids

XI)Weight Effects

The weight of the medium transported or medium used for the test is called as Live Loads. Snow and Ice due to operating and environmental conditions shall be considered.

Similarly, Weight of Piping and Insulations and other superimposed loads supported by the Piping are called as Dead Load 

XII) Thermal Expansion and contraction effects

a)Thermal loads due to restraints -Thrusts and moments when free thermal expansion or contraction is prevented by restraints or anchors.

b) Loads due to temperature gradient-Stresses in pipe walls resulting from large rapid temperature change or from unequal temperature distribution as result from high heat flux through a comparatively thick pipe or Two-phase flow causing bowing of the line.

c)Loads due to the difference in Expansion characteristics- materials with diff coefficients of expansion are combined as in bimetallic lined, Jacketed Piping etc.

XIII)Effects of  Support Anchor and Terminal movements

Effects of movements of the Piping Supports, Anchors, and the connected equipment shall be taken into account.

These movements may result from the thermal expansion of Equipment, Supports, or Anchors, and from the settlement, tidal movements, wind or sway.

XIV) Reduced ductility Effects

This may cause due to the effects of Welding, heat treatment, forming, bending or low Operating temperature. Low Ambient Temperature Expected during the course of Operation shall also be considered

XV) Cyclic effects

Fatigue due to Pressure Cycling, Thermal cycling, and other cyclic loadings

XVI)Air Condensation effects

At Operating Temperature below -191 o C (312 F) in Ambient Air

condensation and Oxygen enrichment occur. This Should be considered in selecting Material, and adequate Shielding measures should be there to prevent adverse effects.