⬇️ Primary load occurs from Sustained loads like dead weight, live weight, internal pressure etc. and are called non-self-limiting loads. Pressure thrust from an expansion joint is used in this article.
⬇️⬇️ Secondary loads occur from thermal expansion loads like temperature change, anchors and restraints etc. and are called self-limiting loads. Thermal expansion in a horizontal pipe loop is used in this article.
⬇️⬇️⬇️ Occasional loads occur from static wind and seismic loads and are considered to act occasionally. Seismic load on a vertical pipe loop is used in this article.
⬇️⬇️ Secondary loads occur from thermal expansion loads like temperature change, anchors and restraints etc. and are called self-limiting loads. Thermal expansion in a horizontal pipe loop is used in this article.
⬇️⬇️⬇️ Occasional loads occur from static wind and seismic loads and are considered to act occasionally. Seismic load on a vertical pipe loop is used in this article.
Primary Stress ⬇️
Primary Stress is generated by internal and external force and moments. Primary stress is not self limiting – even if a part moves, the load causing it does not reduce. In this example, an expansion joint without restraining hardware creates a primary stress on a pipe.
Primary Stress is generated by internal and external force and moments. Primary stress is not self limiting – even if a part moves, the load causing it does not reduce. In this example, an expansion joint without restraining hardware creates a primary stress on a pipe.
Expansion-joint-stress
Pipe stress as reported by Caesar. The untied joint is applying a bending force, which, depending on the stress level, Caesar can report as a fail. This design does not meet the expansion joint manufacturers requirements for guiding and anchoring. The pipe with the tied joint is okay.
Pipe stress as reported by Caesar. The untied joint is applying a bending force, which, depending on the stress level, Caesar can report as a fail. This design does not meet the expansion joint manufacturers requirements for guiding and anchoring. The pipe with the tied joint is okay.
This primary stress is caused by pressure of the fluid multiplied by the area of the pipe. It occurs all the time the system is pressurized. No matter how much the pipe displaces, the untied bellows keeps pushing on it.
Because primary stresses are not relieved by the piping moving or yielding, primary stress limits are set lower than other allowable stresses. For example, if primary stresses managed to get above the yield point, the piping would balloon out and explode. The piping codes keep the primary stresses below the yield point by a factor of safety.
Because primary stresses are not relieved by the piping moving or yielding, primary stress limits are set lower than other allowable stresses. For example, if primary stresses managed to get above the yield point, the piping would balloon out and explode. The piping codes keep the primary stresses below the yield point by a factor of safety.
Secondary Stress ⬇️⬇️
Thermal expansion and contraction happens when a pipe heats up and cools down. The piping system must have enough flexibility to handle the expansion.
Thermal expansion and contraction happens when a pipe heats up and cools down. The piping system must have enough flexibility to handle the expansion.
The stress is caused by the pipe pushing against some fixed restraint. Thermal stresses are “secondary stresses” because they are self-limiting. That is, yielding or deformation of the part reduces the stress.
Higher stresses are allowed than in the primary case because of this self limiting behavior. Stresses above the yield point can be acceptable, however, over time, an accumulation of highly stressed thermal cycles can exceed the fatigue capacity of the material leading to failure.
Higher stresses are allowed than in the primary case because of this self limiting behavior. Stresses above the yield point can be acceptable, however, over time, an accumulation of highly stressed thermal cycles can exceed the fatigue capacity of the material leading to failure.
Occasional Stress ⬇️⬇️⬇️
Wind and seismic loads are occasional. In this example sideways seismic loads create the stress.
Wind and seismic loads are occasional. In this example sideways seismic loads create the stress.
The supports for a loop like this would have to be carefully considered to maintain the flexibility while also providing the required support for seismic loads.
Loads like those induced by seismic events are not expected to occur frequently, so the generated stresses are allowed to be higher than primary loads. Seismic stresses are typically allowed to be 20% higher than primary stresses in ASME piping codes. The equipment should be able to survive these rarely occurring stresses without damage.
The vibration control and sway brace is shipped ready for installation.
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.
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.