What effect will long term crevice corrosion have if it occurs?
One bridge owner speculates that if a (ASTM F436) flat washer of Type 3 chemistry is OK, then why wouldn’t a Type 3 DTI also be OK? While this could be true, there are no tests yet which would prove or disprove this, and a DTI is not just like a flat washer, in that it always has some bumps left within the DTI gap even when “fully flattened”. For this reason, a DTI will probably always have a little crevice remaining, and in that case moisture MAY wick into the unprotected gap causing it to stay wet. Should this occur, ultimately there could be rust pack-out under the bolt head possibly causing distress to the bolt assembly. • The cost of coating a DTI is VERY low cost insurance against future problems. For example, if a 350 ton bridge needs 5000 bolts, the premium cost for black dacromet coating on the DTI’s over that of Type 3 is less than $500, an amount of money which is minuscule when compared to the ultimate cost of cleaning and painting the bridge because the DTI’s continue to c
