2. . 
An organic acid [HCOOH] used in oil- and gas-well stimulation treatments. Formic acid has an advantage over HCl in that formic acid is easier to inhibit against pipe corrosion at temperatures as high as 400°F [204°C]. Formic acid is intermediate in strength between hydrochloric acid [HCl] and acetic acid. Additionally, formic acid corrodes steel more uniformly than does HCl and causes less pitting.