First Practical Experience with Robot Inspection of Ammonia Storage Tanks

Keywords: Ammonia tanks, stress corrosion cracking, SCC, robot inspection, ultrasonic inspection, non-destructive testing.

Refrigerated liquid ammonia in larger volumes is normally stored in carbon steel tanks. These tanks may suffer from ammonia Stress Corrosion Cracking (SCC). Oxygen needs to be present to develop this failure mechanism.

An intrusive inspection of such tanks will include emptying the tank and filling it with air. This is a very time consuming and expensive set of operations that includes the introduction of oxygen, which is not desirable due to the risk of SCC development.

Yara has, together with Force Technology, developed a concept for non-intrusive inspection. A remotely controlled robot is operated on the outside of the liquid-containing tank, inspecting the welds using an ultrasound technique (UT). In the case of a double integrity tank, the robot is operating in an ammonia atmosphere. The concept also includes deployment of the robot.

The concept has been successfully employed on several of Yara’s ammonia tanks in Europe.

Kjetil Bakli¹, Ole Nørrekær Mortensen² and Christian Valand³.

¹ Yara International ASA, Bygg 18, PO Box 1123, N-3905 Porsgrunn, Norway.

² Force Technology, Hovedkontor, Park Allé 345, DK-2605 Brøndby, Denmark.

³ Nokas AS, Træleborgodden 6, N-3112 Tønsberg, Norway.

12 pages, 6 figures, 8 references