Abstract
Increasing interest in utilizing hydrofluoric acid (HF) for acid stimulation of wells in the Gulf of Mexico to improve hydrocarbon productivity raised the question of acid chemical compatibility with existing offshore production system components, particularly riser titanium alloy stress joints (TSJs). A notable concern is elevated corrosion rates and possible absorption of by-product hydrogen on titanium components when exposed to even relatively dilute, cold or warm HF-containing solutions. Unfortunately, conventional film-forming/adsorption type organic inhibitors generally offer limited inhibitive benefits for titanium alloys exposed to inorganic reducing acid media.
This laboratory corrosion test screening program specifically aimed at identifying practical, common inorganic salts which, when added to warm dilute HF solutions, provides effective corrosion inhibition for UNS R56404(1) (ASTM Grade 29 Titanium)(2). The study revealed that aluminum, molybdate, or borate salt additions, and certain combinations thereof, can be potent corrosion inhibitors when added in certain minimum molar ratios to the fluoride present in the acid fluid. Effective inhibition was achieved over the 0.3- 1.0 wt. % HF acid levels and 52-80°C conditions tested, in stationary and flowing fluids. Suggested guidelines for formulating promising injected salt solution concentrates for effectively inhibiting spent HF acid return fluids for titanium components based on these tests are offered.
