Titanium Performance in Anhydrous Methanol - Stress Corrosion Cracking

Background

Anhydrous methanol is able to cause stress corrosion cracking (SCC) in titanium and titanium alloys. Industrial methanol is frequently diluted for safety and the water content (typically 5% by weight) is adequate to provide immunity to titanium and for there to be no problem in most practical applications.

Inhibition of Corrosion in Titanium Alloys

In the past, specification of a minimum content of 2% has proved adequate to protect commercially pure titanium equipment for all but the most severe conditions. The use of methanol with 5% water provides inhibition for all but the most severe conditions of sustained exposure likely to be experienced by the most resistantg titanium alloys used in offshore oil and gas applications. For these alloys containing ruthenium or palladium working at higher temperatures and pressures in more aggressive environments, a revised limit of 10% minimum water content of methanol.

Recommended Water Contents to Prevent Stress Corrosion Cracking in Titanium Alloys

The following table provides conservative guidelines, which are based on room temperature, sodium chloride saturated methanol tests conducted with applied stress at or above the alloy yield strength and/or at low strain rate to failure.

Table 1. Minimum recommended water contents for methanol to prevent stress corrosion cracking in titanium alloys.

Note – Intermittent exposure is defined as short-term non-continuous exposure, while sustained exposure is defined as long-term continuous exposure.

Source: Titanium Information Group

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