The B31.3 Code provides design guidance for primary & secondary stresses. The basic characteristic of a primary stress is that it is not self-limitinI!. ..\5 long as the load is applied, the stress will be present & will not diminish \\~th time or as defonnation takes place. The failure mode of a primary stress. is gross defonnation progressing to rupture. Examples of a primary stress are circumferential stresses due to internal pressure & longitudinal bending stresses due to gravity. The basic characteristic of a secondary stress is that it is self- limiting. The stress will diminish with time and strain. The failure mode of a secondary stress is small crack leading to leakage. Secondary stresses are due to cyclic thermal expansion and contraction.
Wall thickness for Internal PressureCalculate the adequate pipe wall thickness for a given material and design conditions, as follows:
Design of Miters ( Read with Appendix -B)
In all the equations above, T is purchase order thickness i.e. Nominal thickness less mill tolerance.
Design of Branch Connections (Read with Appendix - C)
Blind FlangesBlind flanges are used to stop the flow of content of piping. They are exposed to full longitudinal pressure force. B31.3 provides an equation to calculate the thickness of blind as follows:
Flexibility Analysis Of Piping SystemsThe safety of a piping system subjected to a temperature change and resulting thermal displacement is determined by a flexibility analysis to insure against following:
Displacement Stress Range
Cold spring is the process of offsetting or preloading the piping system with displacement loads i.e. cutting short or long the pipe between two anchors.
Occasional Load Stresses:
Maximum Span for Piping:
Thermal Expansion Analysis:
M = Bending moment
E = Modulus of elasticity
I = Moment of Inertia
∂ = Deflection perpendicular to axis
L = Length of span
Also, the vertical expansion is in the ratio of m : n.
Slope for Piping
c. Angular Rotation and
1. Slip Type/ Telescope TypeIt consists of a slip-element sliding telescopically within fixed piping, serving as outer jacket. The lean… path between jacket and slip element is sealed using packing materials. Compatible with the fluid a operating temperatures.
ii. For easy movements of telescope sleeve, low tightening pressure is required.
food/ pharmaceutical services.
2. Bellows TypeMetallic bellows of compatible materials (using stainless steels) and thinner than piping thickness are to compensate the thermal expansion. Thickness of bellows is of the order of 1.0 to 2.0 mm.
3. Expansion LoopsExpansion loops are of same pipe material. They can absorb bending and torsion of pipe. They are most suitable for high pressure/ temperature applications. However, they occupy larger space and are heavy and bulky. Although several types of configurations are possible, the most preferred is U-type in single plane or two-plane.
Figure 1.3 Chart for determining shell thickness of components under external pressure when constructed of carbon or low alloy steels (specified minimum yield strength 24,000 psi to, but not including, 30,000 psi) [Note (1)]
within this range where other specific charts are referenced) and type 405 and type 410 stainless steels [Note(1)]