Criteria for Correct Installation Direction
1. Flange Face Inward: During installation, the wider flange face of the nut must be tightly against the surface of the connected parts, especially the serrated side, which should contact the connected parts to prevent loosening through mechanical engagement.
2. Threaded End Outward: The threaded portion of the nut should face outward for easy tightening with a wrench or socket tool and for later maintenance.
3. Marking Face Outward: If the nut has a performance grade or manufacturer marking, it is recommended to have the marking face outward for easy inspection and identification later.
Preparation and Confirmation Before Installation
1. Visually Identify the Flange Face
The flange face is usually wider than the nut body and some have serrations (gross teeth) for anti-loosening.
For double-sided nuts, prioritize having the marked side facing outward, and the unmarked or serrated side facing inward.
2. Cleaning and Lubrication
Before installation, remove oil, rust, burrs, and other impurities from the threads, flange face, and surfaces of the connected parts. Apply lubricant (such as molybdenum disulfide grease) evenly to the threaded and nut bearing surfaces to reduce the coefficient of friction and improve tightening accuracy.
Key Controls During Installation
1. Manual Pre-tightening
Align the flange nut with the bolt or threaded post and initially screw it in by hand to avoid forced tightening that could cause thread crossing or damage.
2. Diagonal Step-by-Step Tightening
For multi-bolt connections, apply force gradually in at least three steps in a diagonal or star-shaped sequence (e.g., 50% → 80% → 100% of the design torque) to ensure even pressure distribution and prevent flange misalignment.
3. Using a Torque Wrench
Critical equipment or high-pressure systems must use a torque wrench to accurately apply the pre-tightening force according to the design value and record the data for future reference.
Post-Installation Verification Methods
1. Visual Inspection: Confirm that the flange face is completely flush with the connected parts without gaps; toothed flanges should show slight indentations.
2. Torque Retest: Randomly check key bolts to ensure that the torque is stable and does not regress.
3. Exposed thread inspection: The bolt should have at least two complete threads exposed outside the nut to ensure full engagement.
