Abstract: Many of the causes of Power Plant failures are widely known but still not avoided. In some cases, environmental factors are less obvious and cause unexpected failures.
1) Unexpected failure of a Waste Heat Recovery Unit (WHRU): The unit failed prematurely in six months. The root cause of the failure was corrosive attack of the tube ends at the tube sheath weld joints at the exhaust outlet due to sulfuric acid. Gas entering the Heat Exchanger (HE) was ~873°F and gas exiting was ~350°F. It is well-known that HE operating temperatures should be outside the dew point (~300°F) of sulfuric acid.
2) Unexpected failure of HRSG LP carbon steel economizer tubes due to SCC in three years. Ammonium nitrate salts on the OD of the finned tubes was the likely aggressive species. This is a known environment to cause SCC of carbon steel tubes.
Authors: Fahmida Hossain and Veda-Anne Ulčickas
Keywords: Corrosion, Sulfuric acid dew point, Economizer tubes, Stress corrosion cracking