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.

Titanium Alloy Grade

Minimum Methanol Water Content to Prevent SCC

Intermittent Exposure

Sustained Exposure

CP Grades 1,2,7,11,16,17

2.0%

2.0%

Alloy Grade 9 Ti3Al2.5V

2.0%

2.0%

Alloy Grade 12 Ti0.3Mo0.8Ni

2.0%

2.0%

Alloy Grade 5 Ti6Al4V

3.0%

3.0%

Alloy Grade 23 Ti6Al4V ELI

3.0%

3.0%

Alloy Grade 29 Ti6Al4VRu

5.0%

10.0%

Alloy Grade 28 Ti3Al2.5V1Ru

2.5%

3.0%

Alloy Grade 19 (Beta C)

5.0%

5.0%

Alloy Grade 20 (Beta C + Pd)

5.0%

10.0%

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

For more information on this source please visit Titanium Information Group.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit