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Effective Inorganic Salt Corrosion Inhibitors for Titanium Components Exposed to Dilute Hydrofluoric Acid Well Stimulation Fluids

This laboratory corrosion test screening program is specifically aimed at identifying practical, common inorganic salts which, when added to warm dilute HF solutions, provides effective corrosion inhibition for UNS R56404(ASTM Grade 29 Titanium).

Product Number: 51317--8978-SG
ISBN: 8978 2017 CP
Author: Ronald Schutz
Publication Date: 2017
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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 the known potential for elevated etch rates and consequent hydrogen absorption on titanium components when exposed to even relatively dilute cold or warm HF-containing solutions. Unfortunately conventional film-forming/adsorption type organic inhibitors offer little 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 provide effective corrosion inhibition for UNS R56404 (ASTM Grade 29 Titanium). The study revealed that aluminum molybdate or borate salt additions and certain combinations thereof can be potent etch inhibitors when added in certain minimum molar ratios to the fluoride present. Effective inhibition was achieved over the 0.3- 1.0 wt% HF acid levels and 125F-175F conditions tested in stagnant and flowing fluids. Suggested guidelines for formulating promising injected salt solutions for inhibiting spent HF acid return fluids for titanium components based on this database are offered.

Key words: titanium, well acidizing, acid stimulation, hydrofluoric acid, corrosion inhibitor

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 the known potential for elevated etch rates and consequent hydrogen absorption on titanium components when exposed to even relatively dilute cold or warm HF-containing solutions. Unfortunately conventional film-forming/adsorption type organic inhibitors offer little 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 provide effective corrosion inhibition for UNS R56404 (ASTM Grade 29 Titanium). The study revealed that aluminum molybdate or borate salt additions and certain combinations thereof can be potent etch inhibitors when added in certain minimum molar ratios to the fluoride present. Effective inhibition was achieved over the 0.3- 1.0 wt% HF acid levels and 125F-175F conditions tested in stagnant and flowing fluids. Suggested guidelines for formulating promising injected salt solutions for inhibiting spent HF acid return fluids for titanium components based on this database are offered.

Key words: titanium, well acidizing, acid stimulation, hydrofluoric acid, corrosion inhibitor

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