- Design Pressure and Temperature: Each component thickness must be sufficient to withstand most severe combination of temperature and pressure.
- Ambient effects like pressure reduction due to cooling, fluid expansion effect, possibility of moisture condensation and build up of ice due to atmospheric icing, low ambient temperature etc.
- Dynamic effects like impact force due to external or internal unexpected conditions, Wind force, Earthquake force, Vibration and discharge (Relief valve) reaction forces, cyclic effects etc.
- Component self weight including insulation, rigid body weights along with the medium it transport.
- Thermal expansion and contraction effects due to resistance from free displacement or due to thermal gradients (thermal bowing effect) etc.
- Movement of pipe supports or connected equipments etc.
- one-third of tensile strength at maximum temperature.
- two-thirds of yield strength at maximum temperature.
- for austenitic stainless steels and nickel alloys having similar stress–strain behavior, the lower of two thirds of yield strength and 90% of yield strength at temperature.
- 100% of the average stress for a creep rate of 0.01% per 1 000 h
- 67% of the average stress for rupture at the end of 100 000 h
- 80% of the minimum stress for rupture at the end of 100 000 h
- for structural grade materials, the basic allowable stress shall be 0.92 times the lowest value determined (1) through (6) above.
- Category D Fluid Service: nonflammable, nontoxic, and not damaging to human tissues, the design pressure does not exceed 150 psig, the design temperature is from -20 degree F to 366 degree F.
Category M Fluid Service: a fluid service in which the potential for personnel exposure is judged to be significant and in which a single exposure to a very small quantity of a toxic fluid, caused by leakage, can produce serious irreversible harm to persons on breathing or bodily contact, even when prompt restorative measures are taken.
- Elavated Temperature Fluid service: a fluid service in which the piping metal temperature is sustained equal to or greater than Tcr (Tcr=temperature 25°C (50°F) below the temperature identifying the start of time-dependent properties).
- Normal Fluid Service: a fluid service pertaining to most piping covered by this Code, i.e., not subject to the rules for Category D, Category M, Elevated Temperature, High Pressure, or High Purity Fluid Service.
- High Pressure Fluid Service: a fluid service for which the owner specifies the use of Chapter IX for piping design and construction. High pressure is considered herein to be pressure in excess of that allowed by the ASME B16.5 Class 2500 rating for the specified design temperature and material group.
- High Purity Fluid Service: a fluid service that requires alternative methods of fabrication, inspection, examination, and testing not covered elsewhere in the Code, with the intent to produce a controlled level of cleanness. The term thus applies to piping systems defined for other purposes as high purity, ultra high purity, hygienic, or aseptic.
- if the system duplicates, or replaces without significant change, a system operating with a successful service record (operating successfully for more than 10 years without major failure).
- if the system can readily be judged adequate by comparison with previously analyzed systems.
- if the system is of uniform size, has no more than two points of fixation, no intermediate restraints, and falls within the limitations of empirical equation mentioned below:
Ap = cross-sectional area of pipe
Fa = range of axial forces due to displacement strains between any two conditions being evaluated
ia = axial stress intensification factor. In the absence of more applicable data, ia p 1.0 for elbows, pipe bends, and miter bends (single, closely spaced, and widely spaced), and ia =io (or i when listed) in Appendix D for other components;
it = torsional stress intensification factor. In the absence of more applicable data, it=1.0;
Mt = torsional moment
Sa = axial stress range due to displacement strains= iaXFa/Ap
Sb = resultant bending stress
St = torsional stress= itXMt/2Z
Z = section modulus of pipe
ii = in-plane stress intensification factor from Appendix D
io = out-plane stress intensification factor from Appendix D
Mi = in-plane bending moment
Mo = out-plane bending moment
Sb = resultant bending stress
10. What do you mean by the term “Cold Spring”?
Ans: Cold spring is the intentional initial deformation applied to a piping system during assembly to produce a desired initial displacement and stress. Cold spring is beneficial in that it serves to balance the magnitude of stress under initial and extreme displacement conditions.
When cold spring is properly applied there is less likelihood of overstrain during initial operation; hence, it is recommended especially for piping materials of limited ductility. There is also less deviation from as installed dimensions during initial operation, so that hangers will not be displaced as far from their original settings.
However now a days most of the EPC organizations does not prefer the use of Cold Spring while analysis any system.
11. How to decide whether Reinforcement is required for a piping branch connection or not?
Ans: When a branch connection is made in any parent pipe the pipe connection is weakened by the opening that is made in it. So it is required that the wall thickness after the opening must be sufficiently in excess of the required thickness to sustain the pressure. This requirement is checked by calculating the required reinforcement area (A1) and available reinforcement area (A2+A3+A4) and if available area is more than the required area then no reinforcement is required. Otherwise additional reinforcement need to be added. The equations for calculating the required and available area are listed below for your information from the code. Please refer the code for notations used: