Inspectioneering
Inspectioneering Journal

99 Diseases of Pressure Equipment: Ammonia Stress Corrosion Cracking

By John Reynolds, Principal Consultant at Intertek. This article appears in the November/December 2003 issue of Inspectioneering Journal.
3 Likes

Ammonia stress corrosion cracking (SCC) has been around a long time. Most everyone has experienced it from time to time. It's not uncommon in brass tubes in cooling water service that is contaminated with ammonia due to biological growths or other contamination. Sometimes ammonia is added intentionally to process streams as a neutralizer by folks who do not know what it might do to brass tubes. Brass condenser tubes will fail brittlely when bent after they have significant ammonia stress corrosion cracking present. Eddy current inspection of brass tubulars is effective at finding ammonia cracking. Cupro-nickel alloys are usually not susceptible, and if necessary you can upgrade to austenitic stainless steels (which has it's own set of problems).

Another form of ammonia SCC afflicts carbon steel equipment. Unlike the cracking mechanism on brass, which occurs in an aqueous solution, the cracking of steel equipment occurs in anhydrous ammonia (just the opposite). Adding a very small amount of water (0.2%) to the anhydrous ammonia is enough to inhibit the cracking of steel. Systems that are not PWHT'd are much more susceptible (especially with hard welds), as well as systems that have air/oxygen contamination. Unlike the ammonia SCC of brass tubulars which usually results in some sort of economic or reliability impact, we must be much more careful to avoid ammonia cracking of steel, as the consequence of failure of ammonia systems can be deadly. Ammonia cracking of steel equipment can be readily detected with wet fluorescent magnetic particle examination where access to the surface is available, and shear wave UT from the opposite side where surface availability for examination is limited.

Do the right people in your facilities know about ammonia stress corrosion cracking of brass and steel and do they know their role in preventing it from occurring?


Comments and Discussion

There are no comments yet.

Add a Comment

Please log in or register to participate in comments and discussions.


Inspectioneering Journal

Explore over 20 years of articles written by our team of subject matter experts.

Company Directory

Find relevant products, services, and technologies.

Training Solutions

Improve your skills in key mechanical integrity subjects.

Case Studies

Learn from the experience of others in the industry.

Integripedia

Inspectioneering's index of mechanical integrity topics – built by you.

Industry News

Stay up-to-date with the latest inspection and asset integrity management news.

Blog

Read short articles and insights authored by industry experts.

Expert Interviews

Inspectioneering's archive of interviews with industry subject matter experts.

Event Calendar

Find upcoming conferences, training sessions, online events, and more.

Downloads

Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

Videos & Webinars

Watch educational and informative videos directly related to your profession.

Acronyms

Commonly used asset integrity management and inspection acronyms.