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

The vibration control and sway brace is shipped ready for installation.

Sway Brace

1. Measure the correct space required to install the sway brace assembly. Lay out the sway brace assembly as it is to be installed. Weld one end of structural attachment to the structure and affix the other end with clamp or bolting as required. Make sure the sway brace is located in the same direction as the thermal movement of the pipe. Tighten the adjustment coupling to release the travel stops if supplied. Turn the thrust nut until the bottom of the pressure plate lines up with the pre-load indicated on the nameplate.

2. The brace should be in the proper configuration when it reaches the hot condition. If not, final adjustments can be made by tightening or loosening the adjustment coupling.
i) When properly adjusted, the rod coupling should rotate with slight resistance and the tension test collar can be rotated by hand while holding the rod stationary. There should not be any gap between either end of the pressure and end plates.
ii) Two rod ends should be visible in the adjustment coupling.

When the system shuts down for maintenance, the travel stops should be reinstalled and the same adjustment procedure should be repeated.

⬇️⬇️‘Hot’ sustained stress – method comparison

In the past few years there has been an increased focus on the so-called ‘hot sustained’ stress in piping system analyses. The ASME B31.3 2006 edition clarified that Sustained stress requirements must be met for all operating conditions of a piping system. There had always been practitioners whose view was that any stress due to change in temperature should be considered secondary. You can still find an interesting discussion on this topic in the CAESAR II manual.

If you read Example 2 in B31.3 Appendix S, you will see that it includes a sustained stress check with the inactive/lifting off support removed. When we try to simulate this by using algebraic load cases, we are essentially taking a short cut to avoid having to run a new model with this support removed. In this post we will see why the use of algebraic load cases in this manner can sometimes be too conservative. It applies more to those of you not using CAESAR II Version 8 or above, but is worth knowing either way. In Version 8, the ‘Alternate-sustained’ case facility was introduced, which produces the same results as creating a separate model.

Lets take a look at the typical load cases used for an algebraic ‘hot sustained’ check:

L1) W+P1+T1+D1 (OPE)

L2) W+P1 (SUS)

L3) T1+D1 (OPE)

L4) L1-L3 (SUS)

L5) L1-L2 (EXP)

Load case 3 is an artificial construct which represents weightless thermal expansion (plus imposed boundary displacements). Load case 4 is simply the algebraic subtraction of this effect from the operating case – it may be thought of as applying weight to the pipe in the operating configuration.

Where the algebraic case method can differ significantly from the ‘separate model’ approach is when there are multiple single-acting (+Y) restraints. Fortunately there is an easy way to address this issue.

Let me demonstrate by way of an example. Due to thermal expansion of a process column, the connecting piping shown below lifts off at the support nearest to the column (Node 80). This corresponds to case L1. The support at node 90 is nearly ready to lift off but is still resting.