- ZHUHAI JIALI HARDWARE CO.,LTD.
- +86-756-8586520
Standard Tightening Torque Table For Grade8.8/10.9/12.9 High-strength Bolts, On-site Assembly Torque Construction Specification
Standard Tightening Torque Table For Grade8.8/10.9/12.9 High-strength Bolts, On-site Assembly Torque Construction Specification
Standard Tightening Torque Table For Grade8.8/10.9/12.9 High-strength bolts, On-site Assembly Torque Construction Specification
High-strength bolt connections rely on stable preload for fastening and anti-loosening. Torque control is the core control point of steel structure assembly. Many construction sites tighten bolts by experience. Insufficient torque causes support slippage, excessive torque results in delayed bolt fracture. Connection failure of wind turbine towers and energy storage container steel structures will trigger serious safety accidents.
1. Core Principles For High-strength Bolt Torque Selection
| Working Condition | Reference Torque Coefficient | Risk Description | Applicable Scenario |
| Dry thread without lubrication (galvanized/Dacromet finished) | 0.14 ~ 0.18 | High friction resistance, lower preload under equal torque | Original finished bolts without extra grease |
| Thread coated with lubricating grease | 0.10 ~ 0.13 | Reduced friction, higher risk of overload yield under same torque | Heavy flanges, high temperature equipment bolt assembly |
| Rusted & contaminated thread | Unstable coefficient, standard torque cannot be adopted | Uncontrollable preload | Direct assembly forbidden, clean thread or replace bolts |
2. Multi-stage Tightening Standard Process For Steel Structure
1. Preliminary tightening: Apply 50% standard torque to eliminate sheet gaps and achieve full contact; 2. Re-tightening: Wait at least 15 minutes and apply another 50% torque to compensate sheet rebound; 3. Final tightening: Reach design specified torque. Tighten large flanges in diagonal symmetric sequence; 4. Mark after completion: Make clear marks after final tightening for later loose inspection.
3. Common On-site Problems & Control Points
1. Torque wrench calibration: Industrial torque wrenches require third-party calibration every 6 months; inaccurate tools are prohibited; 2. Lubrication consistency: Maintain unified lubrication status for one batch, avoid mixed dry & lubricated assembly causing uneven preload; 3. Temperature influence: Steel elastic modulus changes under low winter temperature. Random preload sampling and torque adjustment are required if necessary; 4. Time limit rule: If final tightening is delayed more than 24h after preliminary tightening, loosen all bolts and repeat full tightening procedure.