Extracts from an IMCA safety flash concerning workboat and corrosion incidents

The wooden bung found to be the cause of the problem

The wooden bung found to be the cause of the problem

IMCA (International Marine Contractors Association) has reported a number of incidents, extracts of which are published here involving workboat and corrosion incidents, giving suggested recommendations in each case.

Incident one. Incomplete engine service by vessel crew led to an auxiliary power unit engine breakdown.
After servicing of a vessel’s electrical generator (auxiliary power unit) it was found that the motor could not be returned to a functioning service. Initial investigation revealed a lack of coolant movement, causing the motor to overheat which in turn was causing the generator to automatically shut down. Further investigation (not by the crew) found a blockage was located within the coolant line. The blockage was a wooden bung.

When performing a minor repair, a wooden bung had been used to prevent any coolant loss during removal of a pipe. The repair was completed and the pipe was replaced, but without the bung being removed.

Causal factor: poor mechanical practice.

Recommendation: ensure proper record-keeping and logging of events during repairs, particularly when repairs span several shifts, to ensure that what has happened is clearly understood by all involved.

Incident two. Corrosion Damage – Failed Fire Hydrant
An IMCA member has reported an incident in which a fire hydrant valve failed under pressure. The incident occurred during testing of the helideck firefighting system. A hydrant valve assembly on the starboard side of the main deck failed under pressure. The 2kg valve assembly struck the deck head approximately 2 metres above, chipping paint on impact, and then fell to the deck below. No-one was injured. Whilst no-one was in the immediate area, the impact was heard by several people. The force associated with the hydrant valve assembly failure had the potential to cause a significant injury or fatality.

The IMCA member’s investigation revealed the following:
• There was an unexpected failure of the hydrant valve assembly studs. These studs were of type 303 Stainless Steel;
• Expert analysis reveals that type 303 Stainless Steel is particularly susceptible to stress corrosion cracking (SCC) in a high ambient temperature (tropical environment);
• The failure of the studs may have been accelerated by the presence of water surge, or water hammer, in the fire-fighting water system when activating the helideck firewater system;
• Metallurgic analysis examined both “failed” and “non-failed” studs were provided by the vessel. The report stated that the cause of failure was chloride induced SCC, which is a common failure mode for austenitic stainless steels, including types 303, 304, and 316;
• SCC failures commonly occur in tropical environments at ambient conditions for SS 303 and 304 grades, particularly for items under tensile stress and where the item has been cold worked. The report stated that all type 303 studs, regardless of exposure internally to raw seawater or externally to seawater spray would have eventually experienced complete fracture through SCC;
• Equipment on vessels operating in tropical environments, exposed to relatively high environmental temperatures, will be exposed to increased risk of SCC. Austenitic stainless steels (grades 303 and 304 in particular) will fail from SCC in relatively short periods of time;
• A contributing factor to the incident was the incorrect operation of the fire-fighting system inducing water surges or hammer into the fire main;
• The root cause of this incident was the incorrect material specification of the studs for the environment and application.

The IMCA member took the following actions:
Careful consideration given to the increased likelihood of SCC in stainless steel for vessels operating extensively in tropical or high temperature environments, particularly for vessels designed and built in temperate climates;
All affected studs on fire hydrants to be replaced.

Click to read the IMCA Safety Flash in detail: IMCASF35-16