Meaning of Alignment Checking
“Alignment Checking” this term is quite familiar with piping engineers and all construction engineers. During piping installation at the construction site, it is expected that equipment flange should match perfectly (aligned) with the piping flange so that during bolting no problem occurs.
But achieving that perfect alignment is very difficult to achieve. If this alignment for rotary equipment is not proper then there may be several problems in the future during operation which may lead to vibration of equipment/piping system or in some situations equipment failure.
Code Guidelines Regarding Rotary Equipment Alignment
American Petroleum Institute code API RP 686 provides the data for acceptable deviation from the ideal perfect alignment. As per the code if the vertical and horizontal deviation of piping flange and rotary equipment flange centerline is within 1.5 mm and parallelism (rotation) is within 0.0573 degrees then the alignment is accepted otherwise means to be devised to bring the deviation within those values.
While performing stress analysis of rotary equipment connected piping systems in Caesar II we can very easily ensure this limitation. The following write up will describe the step by step method of doing the same.
Alignment check of nozzle flange shall be performed for all Rotating Equipment like Centrifugal Compressor, Steam Turbine, Centrifugal Pumps, Gear Pumps, etc as per the following procedure.
Alignment checking using Caesar II
- Ensure the correct weight of the pipe (with proper thickness), Support weight (dummy pipe), Weight of valves, flanges and any in-line items.
- Consider Insulation density carefully (equivalent insulation density to be correctly fed with insulation & cladding weight, Check insulation on dummies for cold insulated lines).
- Model all branch piping (like drip legs etc.) greater than 2 inches.
- Discuss with a piping lead engineer for the requirement of any maintenance flanges (Normally for steam turbine or centrifugal connected lines the maintenance flange is recommended) and include it if required.
- Minimize the sustained load on the equipment nozzle as much as possible during the static analysis run of the Caesar model.
- Normal industry practice is to analyze the Alignment checking in a separate file. So rename the static file as Filename_Alignment.C2
- Make the equipment nozzle anchor flexible or remove the displacement if the anchor was not modeled.
- Wherever spring support is used, define spring rate and cold load in case of variable effort spring & Constant effort support load in case of constant effort spring.
- After performing the above create one additional load case in Caesar II as mentioned below:
WNC+H SUS System with spring hanger
WNC SUS System without spring hanger
- Set the spring hanger as “As designed”.(Two load cases can be generated for spring As designed and rigid condition)
- Now run the analysis and check the displacements of the nozzle at the above-mentioned load case and limit them within below mentioned values:
Vertical deflection (Normally DY): +/- 1.5 mm
Horizontal displacement (sqrt sum of DX and DZ): +/- 1.5 mm
Parallelism (sqrt sum of RX and RZ): 0.0573 degrees.
- In case, the above limitations are not met then re-analyze by readjusting the spring and other supports and do the simulation.
Few Notes for Alignment Checking
- An alignment check is to be performed for both inlet and outlet lines.
- Alignment check must be performed with spring under both in “As designed” and in “locked” condition.
- To avoid small misalignment in the vertical direction first support from rotary equipment nozzle is used either spring support or adjustable type support.
Few more Useful Resources for you..
Shaft Alignment Methodology for Compressor and Driver
Connection procedure (Alignment) of Process Piping with Rotating Equipments: An Article
Alignment Check Methodology in Piping Stress Analysis using Caesar II
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Piping Design and Layout Basics
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