A failure analysis based on ASME Sec-VIII div-2 was done to evaluate ‘Plastic-Collapse’ & ‘Buckling analysis’ using the elastic & elastic-plastic stress methods, by considering the static loads & dynamic loads in combination that act on the 60” pipe header of the flare system. The results were analyzed for the location of buckling failure that occurred during the 1st Failure recorded. The expansion stresses in the pipe header were twice as much higher than that those due to the normal operating temperature loads and were greatest at the time of the failure, when compared to normal operating temperatures. It was found that the failure in the pipe header characterized as the inward plastic collapse could be attribute to 'Buckling' failure mechanism and that may have been caused by multiple static loads creating the pre-stressed state combined with the dynamic load that triggers the actual failure
The overall vibration characteristics of the 60" flare header piping system, based on the first 15 modes, suggested concerns regarding the presence of maxima / minima and ‘Point of Inflections’ on the 60” section of the main header in the vicinity of Node-3383, which is location of actual failure that occurred during the failure incident. The current configuration of the sulfur lateral branch was also found to provide restraint to the 60" header, such that it is believed to impose unfavorable modes characteristics at the location of actual failure that occurred during the failure incident.
The mode characteristics thus acting on the old (0.375" thickness) header when combined with the high D/t ratio would result in header bending. Under bending, when the cylinder is very long, the flattening of the cross-section leads to large reduction of the effective section modulus of the 60" header, and the instability occurs as a single transverse wave (Buckle) on the compression side of the shell. This phenomenon was attributed to the failure of the 60” sections of flare header piping system. Decreasing the D/t ratio is the most effective way to counter this failure mechanism.
Forwarded from Piping Stress Analysis (PSA Group)
TANK SETTLEMENT:
Forwarded from Piping Stress Analysis (PSA Group)
* Settlement in tanks will be in two stages:
1- Settlement during Hydro Test
2- Long term Settlement
1- Settlement during Hydro Test
2- Long term Settlement
Forwarded from Piping Stress Analysis (PSA Group)
* Settlement during Hydro Test:
This is a one time settlement and usually caused due to the Hydro load during Hydro-testing before the Pre-commissioning stage.
The Tank is Hydro tested separately before connecting the Lines. Hence this settlement is not considered in our Analysis.
This is a one time settlement and usually caused due to the Hydro load during Hydro-testing before the Pre-commissioning stage.
The Tank is Hydro tested separately before connecting the Lines. Hence this settlement is not considered in our Analysis.
Forwarded from Piping Stress Analysis (PSA Group)
* Long Term settlement:
This settlement which takes place during the entire life cycle of the tank. Most settlement occurs during hydro testing of the tank. Gradual settlement continue for years since it's a slow process and it may take more years to reach full settlement. The tank settlement amount depends on soil characteristics-primarily, consolidation and compressibility.
For piping stress analysis only long term settlement is considered.
This settlement which takes place during the entire life cycle of the tank. Most settlement occurs during hydro testing of the tank. Gradual settlement continue for years since it's a slow process and it may take more years to reach full settlement. The tank settlement amount depends on soil characteristics-primarily, consolidation and compressibility.
For piping stress analysis only long term settlement is considered.
Forwarded from Piping Stress Analysis (PSA Group)
Tank bulging-radial growth occurs on the shell due to product static head for large diameter tanks. Bulge formations appear because a static head may cause circumferential and longitudinal strains.
For large-diameter storage tanks( above 36” dia ) with heavy liquid, tank bulging occurs since there is a slight growth of the tank shell in radial direction. When this radial-shell growth occurs at the nozzle location, the nozzle is rotated slightly. Even the smallest nozzle rotation will cause the associated piping to either lift-off from the first support from the tank foundation or excessively compress the pipe at the first support from the tank foundation. This happens even if the vertical displacement of the tank nozzle is in a downward direction. This condition is assumed when the first support is a rigid support from the tank foundation extension.
For large-diameter storage tanks( above 36” dia ) with heavy liquid, tank bulging occurs since there is a slight growth of the tank shell in radial direction. When this radial-shell growth occurs at the nozzle location, the nozzle is rotated slightly. Even the smallest nozzle rotation will cause the associated piping to either lift-off from the first support from the tank foundation or excessively compress the pipe at the first support from the tank foundation. This happens even if the vertical displacement of the tank nozzle is in a downward direction. This condition is assumed when the first support is a rigid support from the tank foundation extension.
Forwarded from Piping Stress Analysis (PSA Group)
TANK BEHAVIOUR: