• Nadirsha Shahabudeen

Various Load Cases In CAESAR II For Piping Stress Analysis

To ensure anatomical and operational integrity, and excellent design Piping stress Analysis is the drill and practice carried out behind the scenes of any piping design project. All piping systems are necessarily exposed to various kinds of loads in their design cycle. These loads establish stresses in the package. Pipe stress engineers typically analyze such systems for stress adopting authentic software such as Caesar II to check that the stress levels are within the admissible limits as detailed by the codes/standards. The following are some of the most prevalent types of loads studied during stress analysis.

The different types of loads are Thermal Loads at Various Operating Condition , Sustained Loads, Seismic Loads, Wind Loads, PSV Reaction Force, Slug Force and Forces Induced by Surge Pressure.The

Thermal Loads at diverse Operating Surroundings

The length of molecular bonds and solids generally expand on heating and contract on cooling as temperature increases. The change due to temperature is calculated using Coefficient in Thermal Expansion (CTE). Thus, to sidestep weakness and wearing resulting from cyclic thermal loads, the piping system should be made flexible.

1. Temperature (Analysis)

Minimum/maximum values as per line list are used for thermal analysis. If lines have design temperature greater than 80 degrees, and the contrast between operating and design temperature is more than 25 degree C then the maximum/minimum operating temperatures, as derived from Process Group, can be adopted in stress analysis rather of design temperature. Also, Piping must also be inspected for the regular operating temperature. Line Design pressure defined in the Line List shall be regarded as the analysis pressure.

2. Sustained Loads

Throughout the plant's operation we can see sustained loads. These mainly subsist of internal pressure and dead-weight. Dead-weight is generally from weight of pipes, fittings, components such as valves, operating fluid, test fluid, insulation, cladding, lining and so on. These are to be considered as follows:

Seismic Loads, Occasional loads and so on

Various international piping codes have set the perimeters that are also called “allowable stresses for sustained loads”, on these axial stresses provoked by dead-weight and pressure in order to shun “failure by collapse”. To achieve the allowable stresses for sustained loads, it is often required to strengthen the piping system vertically.

1. Seismic Loads

Projects that oblige Seismic design to be achieved, there needs to be an equivalent stagnant seismic interpretation in the software to calculate seismic stresses, displacements and loads on the piping systems. Whether the Seismic coefficient has not been brought by the client, the calculation of static seismic co-efficient in terms of ‘g’ – as per project specific information must be considered using relevant codes (UBC/ASCE/SNIP) and others. In this case, the Seismic factor calculation document has to be added to the project stress analysis document. Normal operating temperatures are utilized when considering occasional loads. Seismic loads are seen to be acting along the horizontal axes – along North, South, East, and West directions but not acting at the same time.

2. Occasional loads

These type of loads are installed on piping by unusual events like wind, earthquake etc . Wind loads are regarded for lines with external diameter 14” NB (including insulation) or above and at altitude 10 meters or taller from the ground level. Wind typically blows in the horizontal plane and to protect piping from wind, it is standard practice to fix lateral supports. In the situation of an earthquake, the earth seems to propel vertically and to protect the piping against both horizontal/vertical shift, some resting supports might be composed as essential two way lateral and vertical restraints. Regular operating temperature is used when considering intermittent loads.

3. PSV Reaction Force

If the piping system in query covers PSV (pressure safety valve), then the reaction force due to PSV operation is recognized as useful. While evaluating PSV attached stress systems, the reaction force needs to be assumed. A dynamic load factor equal to 2.0 must be applied on the valve reaction force value. But in case of high reaction force values, the DLF value anticipated as per appendix-II of ASME B31.1 should be utilized. This needs to consider valve data handed over by the vendor.

4. Forces Induced by Surge Pressure

The aftermath of surge on any line is also recognized in stress analysis when spotted by the Process group or a specialist agency. Also, it should be seen that two concurrent intermittent loading shouldn’t be seen in stress analysis.

Piping stress Analysis is a complicated branch — highly knitted with piping layout and support design. Ample flexibility and proper routing are crucial for simplicity and economy of design.Not only optimal design tools and refined software, the best fixes are the ones that handle adept engineering judgment, wisdom and insight.

1. Slug Force

Slug force has to be regarded in stress analysis for lines that have slug flow management. Slug properties can be attained from Process group. The equivalent static analysis in Caesar-II is executed to affect slug loading in piping system using the above formula for calculating slug force.

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