Preliminary alignment is an alignment check made before the baseplate or soleplates are grouted. It confirms that the machines can reach final alignment within the adjustment available, before grouting fixes the position of the mounting plates.
After grouting, correcting a large misalignment usually means repositioning the machines, adding thick shim packs or, in difficult cases, removing and re-pouring the grout. All of these cost time, and some affect long-term reliability. A preliminary check before grouting is a small step that avoids a large problem.
What the standards say
API Recommended Practice 686, Machinery Installation and Installation Design, gives recommended practices for foundations, mounting plate grouting, piping and alignment. The current edition is the second edition of December 2009, reaffirmed in July 2024, with an errata issued in January 2025. API has announced a new structure for the document, split into three parts, which is in development.
API RP 686 is intended to supplement the OEM's instructions, not replace them. Where the OEM specifies its own sequence, tolerances or methods, those apply to its equipment.
What a preliminary alignment check confirms
- The baseplate or soleplates are level and flat within the required tolerance.
- The driver and driven machines can be brought into alignment with reasonable shim packs and available jacking or adjustment range.
- There is enough adjustment margin left for final alignment, including any expected thermal growth offsets.
- Foot contact is good, with no significant soft foot.
- Anchor bolts are correctly positioned and free in their sleeves where sleeves are used.
Common causes of trouble
- Grouting is done to keep to the schedule before alignment has been checked.
- Mounting plates are levelled, but the machines are not checked together as a train.
- Shim packs are already thick before grouting, leaving little room for final alignment.
- Piping is connected before the machines are fixed, pulling them out of position.
A practical sequence
- Release the foundation for machinery work.
- Set, level and check the mounting plates.
- Place the machines and carry out the preliminary alignment check.
- Record the results and confirm the margin left for final alignment.
- Grout, following the grout manufacturer's and OEM's instructions.
- After curing, check level and alignment again, then connect piping and carry out final alignment.
The exact sequence and tolerances depend on the machine, the OEM and the project specification. The point is to check alignment while the position can still be changed easily.
Records
Record the preliminary alignment readings, shim pack thicknesses and soft foot checks on a check sheet that is signed off at the ITP hold point. These records are useful during final alignment and, if a problem appears later, during any failure investigation.