How to Install TurnaSure Direct Tension Indicators (DTIs)

Structural DTI installation for ASTM F959 and F959M DTIs, and other worldwide structural bolt and DTI standards

TurnaSure DTIs are installed in any one of three different ways, see illustration below. Method #1 is recommended when using multiple plies and large bolts as it assures that any undesired movement in the steel plies has not trapped a long bolt. Otherwise ALL methods are good depending on the erector's preference, except that the new TurnaSure curved protrusion DTIs can now be installed under the nut WITHOUT the need or cost of a hardened washer. Because of this significant savings in material, this may prove the most economical method. Assembling the DTI directly under the nut is satisfactory on standard length bolts in the usual two or three ply connections. The installer can judge the gap by eye as it closes while tightening.

SAE Type Tension Indicating Washers described in SAE J2486

Most often, the DTI (or TIW) is placed under the head of a matching Grade 5 or Grade 8 (or class 8.8 or 10.9) cap screw. The nut is turned to tighten the cap screw, and the resulting clamping force begins to flatten the protrusions. Other acceptable methods are shown below, including tightening into a tapped hole. The DTI can be fully flattened, or the .010" feeler gauge can be used as a "no-go" inspection tool inserted between two adjacent protrusions. The notches on the circumference of the DTI show where the gaps are located to ease inspection.

DTIs for studs on gasketed flanges

DTIs for studs on gasketed flanges are usually assembled under the nut with the protrusions facing the nut's bearing surface. Then the torque energy is applied to the nut on the other end of the stud to initiate tightening. (See Assembly Technique1.) The increasing clamping force directly correlates to flattening of the protrusions, which reduces the gap. The "target gap" is pre-selected from the Test Certificate that comes with each production lot of DTIs. The test certificate clearly depicts which gap dimension corresponds to the required tension or clamping force required for the particular application. For example, if a 0.010" gap provides the required load of 50,000 lbs., (60% of yield for a 1 1/8" B7 stud), then when the gap between the DTI and the nut has been reduced to just less than 0.010" the required clamp load has been achieved.

DTIs for Anchor Bolts

DTIs for anchor bolts, studs, and rod are assembled under the nut, with the protrusions bearing directly under the washer face of the nut. As the nut is turned to stretch the anchor bolt, the gap between the nut face and surface of the DTI is reduced proportionally to the tension being induced in the anchor. One of our most commonly used DTI designs has been specially made so that once the DTI is completely flat, the desired level of tension or clamping force is now reliably present in the anchor bolt, stud, or rod.