4.5. The flexibility analysis shall be in accordance with ASME B31.3 and shall be based upon the total displacement strain imposed upon piping system including the effects of equipment settlement or anchor movement, if applicable.

4.6.. The computed stress range shall be less than allowable stress range as defined in ASME B31.3 unless otherwise specified.

4.7. Thermal movements shall be limited to 300mm between anchors and to 100mm at pipe bends or turns. However, greater movements will be considered if the availability of space and the capacity of the anchorage to accept the incremental loads are confirmed.        

4.8. Start-up, shut-down and steam-out where applicable and upset conditions including short-term excursions to higher temperature or pressure as well as normal operating conditions, shall be considered in flexibility analysis. This is particularly pertinent to loads applied to connecting equipment. The effect of vibration from machinery on connecting piping shall also be assessed.             

4.9. Flare system piping shall be designed to take care of expansion, movement or vibration caused by the most severe operating or emergency conditions. Pipe shoes or saddles shall be furnished on the main flare header at all supports.            

4.10. Cold spring shall be used as much as practical to reduce forces on equipment nozzles and to prevent interference from expanding lines.                 

4.11. The use of cold spring for piping systems, which connected to rotating equipment, is prohibited.                

4.12. The combinations of the loads shall conform to the applicable piping code.         

4.13. Impact loads caused pressure relief through a safety valve shall also be calculated in accordance With " API PR 520 ".

5.0 Piping Stress Analysis - Line Classifications

5.1.Each piping system shall be classified as grade “A”, “B” and “C” according to the severity of its design condition and need for special design. Each grade requires the following methods for stress analysis.

Grade “A”: Judgment based on the experience of stress engineer.
Grade “B”: The simplified method according to Para.319.4 of ASME B31.3.
Grade “C”: Formal computer analysis.

5.2. For the following 3” and larger lines, formal computer stress analysis method is required:

1.Process, regeneration and decoking lines to and from Fired Heaters and Steam Generators.
2. Process lines to and from Blowers.
3. Steam lines to and from Turbines.
4. Suction and discharge line of Pumps.
5. Suction and discharge line of Compressors.  

5.3. The judgment of grade for all piping except that connected to rotating equipment shall be in accordance with the criteria shown on fig.1.        

5.4. The judgment of grade for all piping connected to rotating equipment including air fin cooler and fired heater shall be in accordance with the criteria shown on fig.2.

‌6.0. External Load Limits on Equipment

6.1. Rotating Equipment

The allowable nozzle loads for rotating equipments shall be limited to those specified in their governing Engineering specifications and standards to which the equipment is designed, unless otherwise specified by applicable vendors.

For ANSI and ISO pumps, allowable nozzle loads shall be those as other stated in table 2 of API 610 unless otherwise specified by vendors.

6.2. Air Fin-Cooled Exchangers

The allowable nozzle loads for air fin cooled exchanger shall be limited to those specified in Engineering specifications and vendor recommendation and API 661. Piping to air fin cooled exchanger shall be designed to take into account clearances between the frame and the header box of each bundle. And, thrust blocks between tube bundles shall be used whenever possible to minimize friction loads at piping takeoffs and anchors, and to meet allowable loads at the nozzles.

6.3. Exchangers (Shell and Tube)

For piping connected to heat exchangers with T<400°C or P<35 kg/cm2g, the pipe bending stress due to thermal expansion at the exchanger nozzle shall be limited to 700 kg/cm2 using a rigid nozzle analysis. If above criteria is exceeded, localized stress at the nozzle-to-shell be calculated by WRC 107 and WRC 297, and these computed stress value shall be limited in accordance with ASME SECTION VIII.

For piping connected to heat exchangers with T>400°C or P>35 kg/cm2g, the piping imposed loads shall be transmitted to the vendor for his approval.

6.4. Pressure Vessels and Columns

For piping connected to pressure vessels and columns with T<400°C or P<35 kg/cm2g, the pipe bending stress due to thermal expansion at the pressure vessels and columns nozzle shall be limited to 430 kg/cm2 using a rigid nozzle analysis.

If above criteria is exceeded, WRC 107 and WRC 297 shall be used for calculate localized stress at the nozzle-to-shell, and these computed stress value shall be limited in accordance with ASME SECTION VIII.

For piping connected to pressure vessels and columns with T>400°C or P>35 kg/cm2g, the piping imposed loads shall be transmitted to the vendor for his approval.

6.5.  Fired Heaters and Steam Generators

The allowable nozzle loads and moments for fired heater shall be limited to those specified in relevant Engineering specification or API 560 or values that are acceptable to heater vendor.

Displacement of tubes shall be approved by the heater vendor and the effect of expansion and/or displacement of the tubes shall be reflected in the stress analysis of piping system.

Any heater designed with a floating coil (all spring or counter weight mounted) shall be provided with fail-safe limit stops in all directions.

Computer analysis of piping systems connected to floating heater coils shall include the heater coil or an approximate model of the coil as part of systems and the effects of internal guides and restraints. Where heater coils are floating, the support of the connecting piping system shall be completely and independently balanced so that no dead loads imposed on coil.

6.6.  Packaged Equipment

External load limits are to follow the vendor recommendations.

7.0. Piping Restraints    

7.1. Pipe supports shall be spaced so as not to cause excessive deflection at any point along the unsupported section of the pipe. As a general guide for piping located in process area, the maximum mid span deflection shall not be allowed to exceed 12 mm and for piping in pipe way, the mid span deflection between straight run of piping shall not be allowed to exceed 12 mm.           

7.2. The design, selection, fabrication and installation of piping support shall be in accordance with the “Engineering Specification for Piping Hanging and Support”.

7.3. Piping subjected to two-phase flow and connected to reciprocating compressor shall be supported as rigidly as possible while maintaining acceptability of pipe stresses and equipment nozzle loads.

7.4. For nonmetallic piping, vendor’s recommendation for flexibility analysis, support spacing and support type shall be utilized.

8.0.  Miscellaneous

8.1. Reports

Final calculation of the grade “C” and the grade “B” which are analyzed by formal computer analysis will be submitted to owner for record and site modification of piping. The piping systems which are classified as grade “B” shall be analyzed by formal computer analysis if experienced stress engineers decide it necessary to prove that the systems meet the allowance of this specification. The reports shall comprise of the following:

❗️Basic data and calculated conditions
❗️Layout isometric and support type and location
❗️Load cases and calculated member stresses
❗️Forces, moments and displacement reports
❗️Spring hanger and expansion joint design parameters

8.2. Units

Metric units (kg, mm, kg-m, kg/cm2) shall be used as a unit of control for analysis.

8.3. Softwares 

CAESAR II Ver x.xx (produced by COADE Inc.) will be used for formal computer analysis.

Expansion loop

PSV Calculation and Philosophy

⬇️VIBRATION CONTROL AND SWAY BRACES