Correct the plumb condition by lifting the low side at engineered jacking points and installing shims beneath the intended load-bearing locations. Do not use anchor bolts to pull a 30-ton, 30 m stripper column into alignment; that practice can overload the bolts, distort the base, and hide stored force. Shimming can correct tilt, but lateral position or rotation requires a separate movement plan.
Symptom Pattern and Required Correction
The term alignment here means three independent conditions: verticality, lateral position, and rotational orientation. A vertical survey establishes verticality by comparing the vessel centerline or shell position at two or more elevations. Nozzle orientation, centerline coordinates, and anchor-bolt clearance establish the other two conditions.
| Observed condition | Required action | Can base shimming correct it? |
|---|---|---|
| Top displaced relative to the base | Change the base support plane | Yes, if the support and jacking design permit it |
| Base centerline at the wrong coordinate | Translate the vessel laterally | No |
| Nozzles at the wrong angular orientation | Rotate the vessel about its vertical axis | No |
| Survey changes when piping is connected | Remove pipe strain before final alignment | Shims alone do not correct the external load |
| Apparent lean changes with observation direction | Repeat a two-axis survey and check instrument setup | Only after confirming the measured tilt |
Record both magnitude and direction of the out-of-plumb condition. A single reading from one direction cannot define the correction plane. Also check whether the vessel is already on anchor bolts, whether grout is present, and which parts of the base are designed to carry load.
Base-Shim Geometry
Tilting occurs because opposite sides of the base sit at different elevations. For a small angular error, the required elevation difference across the effective support span follows similar-triangle geometry:
Δh ≈ B × x / H
Here, Δh is the required elevation difference across the base, B is the effective support span measured in the direction of lean, x is the horizontal offset between the upper and lower survey elevations, and H is the vertical distance between those survey elevations. Use the same length units for all four terms.
For the stated 30 m column, use 30 m as H only when the readings actually span that full height. If the instrument compares points separated by a shorter vertical distance, use that measured separation. Use the support span from the vessel or foundation drawing; overall vessel diameter is not automatically the correct value.
The formula gives the differential correction, not the thickness of every shim. Establish a reference elevation, then distribute the correction around the support circumference or among the defined support points. With tilt in two axes, resolve the survey into orthogonal components and calculate the required support-plane slope in both directions.
Pre-Jacking Decisions
The support arrangement controls the work method. Review the vessel drawings, foundation details, base-ring or leg geometry, anchor-bolt arrangement, center of gravity, operating loads, connected piping, and designated jacking or shimming locations. A base ring, individual legs, and discrete support lugs require different load-transfer details.
Do not select jacks merely by dividing the stated 30-ton weight by the number of jacks. Jack reactions depend on center-of-gravity position, support stiffness, lift sequence, piping loads, uneven contact, and the temporary load path. A qualified structural or mechanical engineer must define jack locations, reaction limits, temporary supports, and permissible lift before field work begins.
| Decision | Required basis | Wrong practice |
|---|---|---|
| Jacking point | Approved load-bearing detail or engineered fixture | Placing a jack under thin shell, skirt, or unsupported plate |
| Shim location | Permanent support load path | Using a narrow wedge that creates a point load |
| Anchor condition | Drawing and approved work sequence | Pulling the vessel down with anchor nuts |
| Pipe condition | Measured freedom from imposed load | Aligning against connected, strained piping |
| Temporary support | Rated, positively restrained support arrangement | Relying on hydraulic pressure while inserting shims |
Controlled Shimming Procedure
- Establish the baseline. Survey the vessel in two perpendicular directions at defined elevations. Mark the low side, record the offset vector, and confirm instrument setup from an independent position.
- Inspect restraints. Identify grout, anchor-bolt engagement, clips, piping, platforms, ducts, and electrical connections that could resist movement. Obtain an approved disposition before releasing or disturbing any restraint.
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Calculate the correction. Apply
Δh ≈ B × x / Hin the direction of lean. Translate the result into shim thicknesses at the actual support points. - Prepare the load-transfer system. Install engineered jacking fixtures, jacks, cribbing, and positive mechanical supports. Arrange access so personnel can place shims without entering beneath an unsupported load.
- Release only the specified interfaces. Loosen anchors or remove grout only as directed by the approved plan. Do not cut, bend, or force anchor bolts to create clearance.
- Lift incrementally. Raise the designated side in controlled increments while monitoring jack reactions, base deformation, anchor clearance, vessel movement, and piping interfaces. Stop if the vessel translates, twists, binds, or produces unexpected deformation.
- Install permanent shims. Place clean, flat shims at the intended bearing locations. Build a stable pack with broad contact; avoid loose fragments, excessive thin layers, and unsupported tapered edges.
- Transfer the load. Lower the vessel onto the shim packs in a controlled sequence. Confirm that the permanent support carries the load before removing jacks or mechanical supports.
- Restore permanent interfaces. Treat anchors, grout, and connected services according to the vessel and foundation drawings. Apply specified anchor tightening values from the approved documentation rather than selecting a field value.
Verification Readings
- Check 1—Two-axis verticality: expect the measured offset or angularity in each axis to meet the tolerance stated on the project, vessel, or installation drawing.
- Check 2—Load-transfer stability: expect no significant survey change when hydraulic pressure is released and the vessel rests fully on its permanent supports.
- Check 3—Base bearing: expect each designated shim location to have stable, broad contact with no rocking, loose pack, or visible local distortion.
- Check 4—Anchor condition: expect bolts to remain centered within the available clearance, free from bending or forced side contact, with tightening completed to the documented value.
- Check 5—External-load response: expect verticality and nozzle position to remain within specified tolerances after piping and other released interfaces are restored.
Record final readings, instrument locations, survey elevations, shim thickness at each support point, anchor condition, and the sequence used to transfer load. These records distinguish a stable geometric correction from a temporary reading produced by jack pressure or pipe strain.
Recurring Alignment Pitfalls
Anchor-bolt pulling is the most serious wrong practice. It forces the base toward the foundation without creating a controlled bearing plane, so bolt tension and base-plate bending may hold an apparently acceptable survey reading. The reading can shift when the vessel is released, grouted, heated, or connected to piping.
Another common error is treating top offset as shim thickness. The correction scales with the ratio of support span to survey height; installing a shim equal to the measured top offset will generally overcorrect the vessel. Incorrect measurement height and using shell diameter instead of effective support span cause similar errors.
Survey error can also resemble vessel movement. Check instrument level, line of sight, reference stability, shell surface irregularity, and thermal effects. Measure from repeatable targets or defined centerline references rather than an arbitrary shell point.
Finally, a shim is part of the load path, not merely an adjustment gauge. Concentrated bearing, unstable stacks, corroded material, or gaps beneath the support can produce settlement and renewed misalignment after the jacks leave.
Frequently Asked Questions
Can I align a 30-ton vertical vessel without a crane?
Yes, if an engineered jacking and temporary-support system can lift the required side safely. The design must account for actual reactions, center of gravity, support stiffness, restraints, and access for shim placement.
Can I use the anchor bolts to pull the column plumb?
No. Anchor pulling can bend bolts, distort the base, and create a survey result held by stored force rather than stable bearing.
Does shim thickness equal the measured top offset?
No. Calculate the differential correction using Δh ≈ B × x / H, where B is effective support span and H is the separation between survey elevations.
Can I stack several thin shims under the vessel base?
Use a stable, broad-contact pack at each designated bearing point. Avoid excessive thin layers, loose pieces, and unsupported edges because they can slip or settle.
Does alignment end when the vessel first reads plumb?
No. The final verification step is to repeat the two-axis survey after jack pressure is removed, permanent supports carry the load, anchors are restored, and disconnected piping or other interfaces are reconnected; expect every reading to remain within the documented tolerance.