In the structural steel erection industry, efficiency and verifiable safety are paramount. Self-indicating DTI washers revolutionize bolt tensioning by providing a clear, green visual confirmation the exact moment the required tension is achieved. This innovative system eliminates the need for time-consuming feeler gauge inspections on every bolt, dramatically accelerating erection times while ensuring absolute compliance with stringent AS/NZS standards. For structural engineers, fabricators, and erection contractors demanding certainty in their bolting assemblies, the FULLERKREG DTI washer collection offers unparalleled reliability. If you need technical guidance on integrating self-indicating technology into your AS 4100 projects or require a project-specific quote, please reach out to our engineering team at sales@fullerkr.com.
How Self-Indicating DTI Washers Work
Three Stages of Self-Indication
Stage 1: Snug Tightening. During the initial snugging phase, the structural hardened washer comes into firm contact with the raised protrusions of the DTI. At this stage, the compression is minimal, and the green visual indicator remains fully contained within the engineered pockets. There is no visible indication.
Stage 2: Final Tensioning. As the bolt is tightened to its final tension, the massive clamping force begins to plastically deform the raised protrusions. Concurrently, carefully calibrated reduced-height pockets are compressed, forcefully releasing the high-visibility green elastomer outward.
Stage 3: Confirmation. The installation is complete when the volume of the extruded green elastomer matches the reference sample. This reference sample is generated during the pre-installation verification phase, where the visual squirt is perfectly correlated to the specified tension using a 0.125mm feeler gauge.
Top-Elastomer Design Advantage
- Optimal contact surface: The elastomer is extruded against the smooth, uniform surface of the hardened structural washer rather than the rough steel substrate.
- Eliminates loss in oversized holes: Because it extrudes from the top, the indicator cannot be lost down the gap of oversized or slotted holes.
- Controlled release: The extrusion behaves consistently regardless of the condition, roughness, or slope of the underlying structural steel.
- Universal compatibility: Works flawlessly on plain, galvanized, painted, or heavily weathered steel surfaces without absorbing into porous coatings.
AS/NZS 5131:2016 and AS 4100 Compliance
Permitted Tensioning Methods
- Part-turn method
- Direct Tension Indicator (DTI) method
CRITICAL PROHIBITION: AS/NZS 5131:2016 strictly DOES NOT permit the torque wrench method for final tensioning due to the highly unreliable correlation between applied torque and actual bolt tension.
Why Self-Indicating DTIs Excel
- Clear visual vs reference: Inspectors can verify tension instantly from a distance by observing the green indicator, rather than relying on unreliable torque charts.
- Faster than feeler gauge: Drastically reduces the time spent manually checking gaps with feeler gauges on every single bolt.
- More precise than part-turn: Eliminates human error regarding the starting "snug" point and rotation angle measurement.
- No torque dependency: Operates entirely on direct mechanical compression, completely bypassing the variables of friction and lubrication.
Pre-Installation Testing Requirements (AS 4100)
- Test a minimum of 3 samples per diameter, length, and material heat lot.
- Testing must be performed by the exact same erection team using the exact same tools that will be used on the structure.
- The assembly must achieve a minimum of 1.05 × the AS 4100 specified tension.
- Testing must be conducted in a calibrated tension-measuring device (e.g., Skidmore-Wilhelm) to establish the visual reference sample.
Minimum Bolt Tension
| Bolt Diameter | Min. Bolt Tension AS 4100 (kN) | Min. Requirement @ 1.05× (kN) |
|---|---|---|
| M16 | 95 | 100 |
| M20 | 145 | 153 |
| M24 | 210 | 221 |
| M30 | 335 | 352 |
| M36 | 490 | 515 |
UV and Low-Light Inspection Capability
- Poorly lit sites: The specialized green elastomer fluoresces brilliantly under UV light, making it highly visible in dark areas.
- Nighttime inspection: Allows QC teams to rapidly verify entire connections during night shifts without needing massive floodlights.
- Enclosed cavities: Ideal for inspecting bolts inside box girders, shafts, or deep structural profiles using just a portable UV torch.
- Overcast weather: Maintains high visibility even on dreary, low-contrast construction days.
Installation Procedure for Self-Indicating DTIs
- Step 1: Prepare and Align — Secure the joint using drift pins to align the holes. Never use the structural bolts as drift pins.
- Step 2: Position DTI — Place the DTI under the component that will be turned. If the DTI is placed under the bolt head, an additional hardened structural washer must be used under the nut.
- Step 3: Snug-Tight — Use an impact wrench or podger spanner to bring the steel plies into firm contact. Do not fully compress the DTI at this stage.
- Step 4: Final Tensioning — Tension the assembly until the green elastomer is clearly visible and its volume matches the established reference sample.
Marking, Traceability, and Certification
- Every FULLERKREG DTI carries a unique trace number linking it to its specific mill test report.
- Property class markings clearly indicate the designed tension capacity.
- The manufacturer's mark ensures absolute accountability and single-source compliance.
Chemical Composition (Carbon Steel)
| C (%) | Mn (%) | P (max %) | S (max %) |
|---|---|---|---|
| 0.30 - 0.55 | 0.50 - 0.90 | 0.04 | 0.05 |
Mechanical Properties
| Property | M16 | M20 | M24 | M30 | M36 |
|---|---|---|---|---|---|
| Min bolt tension at full indication (kN) | 91 | 142 | 205 | 326 | 475 |
| Inspection gap (mm) | 0.125 | 0.125 | 0.125 | 0.125 | 0.125 |
| Hardness max (HRC) | 37 | 37 | 37 | 37 | 37 |
Benefits by Stakeholder
For Project Owners
Dramatically reduces erection and inspection times, translating directly to massive cost savings and earlier project handovers.
For Engineers
Provides visual, undeniable assurance that the designed clamping force has been achieved across the entire structure, regardless of field conditions.
For Fabricators
Offers a simple, highly efficient bolting solution that minimizes rework and eliminates complex torque calibration disputes.
For Erectors
Ensures fast, safe erection with flexible installation timing, allowing crews to verify tension visually without hauling gauges around the steelwork.
For Inspectors
Makes the inspection process quick, easy, and incredibly safe. The UV capability allows for rapid verification from a safe distance, even in poor lighting.
Competent Person Requirement
AS/NZS 5131 strictly mandates that all high-strength bolting must be undertaken by a "competent person." This requires documented training and demonstrable skills in pre-installation testing and execution. FULLERKREG provides comprehensive technical data and training support to ensure your crews meet these rigorous competency standards.
Fastener Storage Requirements
- Keep all components in their original, sealed packaging until immediately before use.
- Store in dry, covered facilities, completely protected from the weather.
- Prevent exposure to dirt, dust, and moisture that can alter friction characteristics.
- Use only in their unmodified, original manufactured condition.
FAQ
-
What is a self-indicating DTI washer?
It is a Direct Tension Indicator that extrudes a highly visible green elastomer when the bolt reaches the correct tension, eliminating the need for feeler gauges. -
How does the green visual indication work?
As the DTI protrusions are compressed by the required clamping force, internal pockets are crushed, forcefully extruding the green silicone indicator. -
Can self-indicating DTIs be inspected at night or in poor lighting?
Yes. The green elastomer fluoresces brilliantly under UV light, making nighttime or enclosed cavity inspections incredibly fast and safe. -
What is the pre-installation testing requirement for AS 4100?
You must test at least 3 samples per lot using a Skidmore-Wilhelm device to ensure they achieve 1.05× the minimum specified tension and to create a visual reference sample. -
Why is the top-elastomer design better than side-extrusion systems?
The top-elastomer design extrudes against a smooth hardened washer rather than the rough steel, preventing the indicator from being lost in oversized holes or absorbed by porous paints. -
Where can I buy self-indicating DTI washers for AS/NZS projects?
You can source fully compliant indicators directly from the FULLERKREG DTI washer collection. For AS/NZS specific quotes, email us at sales@fullerkr.com.
Conclusion
Self-indicating DTI washers are the future of structural steel erection, combining the absolute mechanical certainty of direct tension indication with the speed of a visual check. By adopting this technology, you ensure strict AS/NZS compliance while drastically reducing inspection overhead. Upgrade your bolting efficiency with the industry's best indicators.
Shop FULLERKREG Self-Indicating DTIs
Email us at: sales@fullerkr.com