11. Whether the expansion stress range has been checked in between maximum and minimum temperatures for which the piping system will be subjected?
12. Whether the effect of friction on sliding support loads been considered?
13. Whether the use of low friction pads been properly marked if used?
14. Whether the analysis is performed for the system with and without friction to check the effect of friction (to determine the worst case) as friction is not something that can be relied on? The harmful effects of friction need to be considered but not the benefits.
15. Whether the Caesar plot and isometric plot are matching with 3D plot?
16. Whether the loads on connected equipment are within allowable limit?
17. Whether the thermal effects of pipe supports, equipment supports been considered?
18. Whether the flange weight includes weight of bolting? In large size piping bolt weights become significant?
19. Whether all possible load cases (start up, shutdown, regeneration, any special process consideration) are considered in analysis?
20. Whether proper ambient temperature is used for the location?
21. Whether spring are modeled properly and selected considering all operating temperature cases?
22. Whether adequate documentation in case of gapped restraints (or any special consideration) are mentioned in isometric clearly to assure that supports will be installed in that manner in construction site?
23. Whether there is a possibility of elastic follow up or strain contentration condition?
24. Whether radial thermal expansion has been considered for line sizes greater than 24 inch NB?
25. Whether hot sustained check has been performed?
26. Whether pressure thrust has been considered while using expansion joints?
27. Whether a flanged elbow has been considered?
28. Whether sustained deflection and thermal displacements are within limit specified by project document?
29. Whether the SIF limitation been considered for large D/t piping?
30. Whether pressure stiffening of bends has been considered in analysis?
31. Whether flange leakage has been performed as per specification?
32. Whether change in pipe length due to internal pressure has been considered?
33. Whether all stresses are are within code limits?
34. Whether variability of springs is within 10% near rotary/critical equipments and 25% for others?
35. Whether thermal displacements more than 50 mm are marked on isometric?
36. Whether support loads are checked and discussed with layout/design?
37. Whether feasibility of all supports has been checked?
38. Whether routing change and special support requirements has been clearly marked in stress isometric and informed to layout/design group?
39. Whether spiders are modelled properly at appropriate intervals for jacketed pipes?
40. Whether weight of hot tapping machine and related equipments are considered in specific situations?
41. Whether alignment checking (WNC file) has been performed for all rotary equipments as per API RP 686?
42. Whether PSV forces are considered for open discharge PSV systems?
43. Whether Hot-Cold and Operating-Standby philosophy has been used when required?

Rigid Strut :

Rigid Strut

This article will explain the step by step methods for modeling the Rigid Strut using software Caesar II.

1 - Find out the direction in which restriction of movement is required (Assume X direction) and location of the strut installation. For reducing thermal loads to be carried by rigid struts it is preferable to choose thermal null points if feasible.

2- Double click on restraints check box in Caesar spreadsheet and model restraint X with 0 mm gap and with no friction. Keep stiffness K1 box blank.

3- Run Caesar Analysis and found out the force in that node.

4- Enter into any catalogue (like C&P, Lisega etc) and select appropriate rigid strut depending on that force (For your reference strut selection table has been reproduced in Fig. 1 from C&P Catalogue).

5- Obtain the stiffness value for the strut from the catalogue and enter this value in restraint stiffness (K1) which u left blank in initial stage.

6- Run the analysis to obtain results.

Fig. 1: Strut Selection Table from C&P Catalogue.

Note: Rigid Struts are used in Turbine and Compressor connected lines near the nozzle connections to take the advantage of very less friction. Otherwise struts can be used as a substitute for guide supports where structure is not available for using standard guides.

Static Analysis of Slug flow:

1- Slug Flow is typical two phase flow where a wave is picked up periodically by the rapidly moving gas to form a frothy slug, which passes along the pipe at a greater velocity than the average liquid velocity.

2- In this type of flow, slugs can cause severe and, in some cases, dangerous vibrations in piping systems because of the impact of the high-velocity slugs against fittings such as bend, Tee etc.

3- Slug flows generate dynamic fluid forces, which may induce structural vibration.

Slug

4- Excessive vibration may lead to component failures due to fatigue or resonance.

5- Such vibration problem may be avoided by thorough analysis, preferably at design stage.

6- Two types of Analysis Methods are prevalent:
a) Static Analysis
b) Dynamic Analysis

7- Examples of Slug flow:
a) Vacuum Transfer Lines
b) Condenser Outlet Lines
c) Re-boiler Return Lines
d) Fired Heater outlets
e) Boiler Blow down lines.