Method and Emphasis points
David Cohen – 29/09/14
• The Most important reason stress analysis is carried out is : SAFETY
• This is achieved by designing a Code Compliant System.
• There are also Financial Saving to be made:
• Correct pipe support spans
• Material sizes and thickness which are correctly specified.
Good practice engineering, Quality controls, Experienced engineers,
and correct installation should avoid dangerous consequences
Buried Pipes : along roads and in civil areas.
HIDDEN DANGERS should be
• Design and Analysis should take into account also construction feasibility
• The designer should run different analyses according to specifying steps.
• Loading Codes:
• Seismic Loads: SI-413
• Wind Loads: SI-414
• Traffic and Earth Loads: ASCE-Guidelines for the design of buried steel pipe
& Geotechnical Report
• Piping Codes:
• ASME B31.3
• ASME B31.8
• NEN 3650
Sources for generation of stress in a Piping System:
•Occasional Loads due to wind, seismic disturbances, PSV discharge etc.
•Forces due to Vibration.
1.Sustained Stresses are the stresses generated by sustained loads. (e.g. Pressure , Weight). These loads are present
continuously throughout plant life.
2.Resistive force arising out of sustained stresses balance the external forces keeping the system in equilibrium. Exceeding
sustain allowable stress value causes catastrophic failure of the system.
3.As per ASME B 31.3, (clause 302.3.5) “ The sum of the longitudinal stresses, SL, in any component in a piping system,
due to sustained loads such as pressure and weight, shall not exceed the product Sh x W ”. Where, Sh=Basic allowable
stress at maximum metal temperature expected during the displacement cycle and W=weld joint strength reduction factor.
4.Pressure Stresses are taken care of by calculating and selecting proper pipe thickness. The pressure thickness (t) of a
straight pipe can be obtained as per ASME B31.3 from the equation (Clause 304.1.2).
The supports should be in
accordance with actual
structures, and not “in the air”
The supports should be
Coefficient of friction factor depending upon the supporting interface (i.e,
junction between Top of Steel and Bottom of Pipe or Bottom of Shoe/Cradle)
shall be applied at all vertical restraint (+Y or Y supports) locations as
Carbon Steel to Carbon Steel: 0.3
Polished Stainless Steel to Polished Stainless Steel/Graphite: 0.15
Teflon to Teflon/ Polished Stainless Steel: 0.10
Concrete to Carbon Steel: 0.4
Pipe to Roll Support: 0.01
Teflon to Carbon Steel: 0.2
Check the Model
From Piping design to stress analysis, just
check that any design problem will occur.
PIPING Redesign will generate a new
stress analysis process.
From Soil Report
Soil Data should be inserted according to soil
report , pipe diameter and pipe depth.
ALL Line Numbers should be written
Only on main lines (not for vents)
ALL Supports should be with different
name , check duplicity (line stop should
be the same support name)