Why Shimming Tolerances Matter
Every pipeline and piping system has design tolerances that define how much deviation from the ideal elevation and alignment is acceptable at each pipe support. Shims are the primary tool for achieving these tolerances in the field. Understanding the applicable standards ensures your shimming meets project requirements and passes inspection.
Common Piping Codes and Standards
Several industry codes and standards establish requirements that affect shimming practices on pipeline and process piping projects:
Key Standards
- ASME B31.3: Process Piping code, widely used in petrochemical and refinery projects. Defines requirements for pipe support and alignment.
- ASME B31.1: Power Piping code for power plant applications with specific support requirements.
- CSA Z662: Canadian standard for oil and gas pipeline systems, governing pipeline construction in Canada.
- API 610/686: Standards for rotating equipment alignment that often drive pipe support shimming accuracy.
- MSS SP-58/SP-69: Manufacturers Standardization Society standards for pipe hangers and supports.
Typical Elevation Tolerances
While specific tolerances vary by project specification, common industry practices for pipe support elevation include:
- General piping: Plus or minus 3 mm (1/8 inch) from design elevation
- Equipment connections: Plus or minus 1.5 mm (1/16 inch) at pump and compressor nozzles
- Large bore piping: Plus or minus 6 mm (1/4 inch) for lines 24 inches and larger
- Critical service: Plus or minus 1 mm for high-temperature or high-pressure systems
Always refer to the project-specific piping specification and engineering drawings for the exact tolerance requirements. Generic code requirements may be tightened by the engineering contractor.
Alignment Tolerances
In addition to vertical elevation, pipe supports must be aligned horizontally. Lateral misalignment at a support can cause unintended loads on the piping and adjacent supports. Typical lateral alignment tolerances range from 3 mm to 6 mm depending on pipe size and service.
Shim Pack Height Limits
Most project specifications set a maximum allowable shim pack height. Exceeding this limit indicates a structural steel or foundation issue that should be corrected rather than compensated with excessive shimming.
Common Shim Pack Limits
- Typical maximum: 25 mm (1 inch) total shim pack thickness
- Some projects allow: Up to 50 mm (2 inches) with engineering approval
- Minimum shim count: Many specs require no more than 4-5 individual shims per pack to prevent instability
- Full bearing required: Shims must provide full bearing contact across the support width
Material Requirements
Piping codes and project specifications typically require shim materials to be compatible with the pipe support and structural steel. Carbon steel shims are standard for most applications, while stainless steel shims are required where corrosion resistance is needed or where galvanic corrosion between dissimilar metals is a concern.
Documentation Requirements
Most piping codes require that shimming be documented as part of the as-built records. This documentation should include the shim dimensions, material, and location at each support point. Digital tools like ShimSheet make it easy to capture this data in the field and generate reports that meet documentation requirements.
How ShimSheet Helps Meet Tolerance Requirements
- Precise recording: Enter exact shim dimensions at each support for accurate documentation
- Pack tracking: Track individual shims within each pack to verify compliance with pack height limits
- PDF reports: Generate professional reports that satisfy client and code documentation requirements
- Project organization: Group shim data by system, area, or line number for systematic verification
Document Your Shimming to Code Standards
Use ShimSheet to track every shim dimension and generate reports that meet piping code documentation requirements.
Try ShimSheet FreeFrequently Asked Questions
What is the typical tolerance for pipe support shimming?
Most projects specify plus or minus 3 mm (1/8 inch) for general piping and tighter tolerances of 1-2 mm at equipment connections. Always check the project specification for exact requirements.
Is there a maximum shim pack height?
Yes. Most specifications limit total shim pack thickness to 25-50 mm (1-2 inches). Packs exceeding the limit typically require engineering review and may indicate a structural issue that needs correction.
What standards apply to pipeline shimming?
Common standards include ASME B31.3 for process piping, ASME B31.1 for power piping, CSA Z662 for Canadian oil and gas pipelines, and MSS SP-58/SP-69 for pipe hanger and support practices.