Electrolytic corrosion: Failure of fire hose couplings

  • Safety Flash
  • Published on 9 February 2023
  • Generated on 14 November 2024
  • 3 minute read

During routine pressure/leak testing, a fire hose fitting failed at the neck of the stub inserted into the hose

What happened?

During routine pressure/leak testing, a fire hose fitting failed at the neck of the stub inserted into the hose.

As part of annual testing of the fire hydrant hoses, two crew were assigned to conduct leak testing of the main deck fire hoses.

A Number 3 hose (20 m x 52 mm (2”)) was connected to a fire hydrant valve and nozzle and visual inspections of the hose and valve conducted prior to testing. 

During the test it was noted that one end of the fire hose had disconnected.

The test was stopped, and further investigation was conducted.

Electrolytic corrosion. Initial  investigation indicated that this hose  appeared to be of a different type from  most of the hoses onboard which were  made up with an aluminium ‘floating’  flange. This hose had a Storz ‘C’  coupling, which was thought to have  flanges fixed to the hose neck. Removal  of the rubber sleeve covering the  seizing wire revealed conventional  Monel seizing wire, and indications  were present that water had been  retained in the fabric outer sleeve  under the rubber sleeve

Damage to failed fire hose coupling

During routine pressure/leak testing, a fire hose fitting failed at the neck of the stub inserted into the hose. As part  of annual testing of the fire hydrant hoses, two crew were assigned to conduct leak testing of the main deck fire  hoses. A Number 3 hose (20m x 52mm (2”)) was connected to a fire hydrant valve and nozzle and visual inspections  of the hose and valve conducted prior to testing. During the test it was noted that one end of the fire hose had  disconnected.

Damaged fire hose coupling

Investigation of the coupling from the other end of the hose showed no immediate signs of concern. However,  there were some small pitting marks evident on the inside of the hose neck and removal of the rubber sleeve  showed more indications of corrosion. Attempts to free off the floating flange caused the fitting to fail. It was also  noted that corrosion was almost as advanced on this coupling as on the fitting which failed

Second end of hose, fitting in similar condition

Inside the coupling, a steel retaining  ring was found buried in the powdery  aluminium oxides, confirming that the  coupling was in fact the same as the  others onboard. But due to corrosion,  the floating part was tightly seized on  the hose barb shaft

Further view of damage

What went wrong?

Electrolytic corrosion.

Initial investigation indicated that this hose appeared to be of a different type from most of the hoses onboard which were made up with an aluminium ‘floating’ flange. 

This hose had a Storz ‘C’ coupling, which was thought to have flanges fixed to the hose neck.

Removal of the rubber sleeve covering the seizing wire revealed conventional Monel seizing wire, and indications were present that water had been retained in the fabric outer sleeve under the rubber sleeve.

Inside the coupling, a steel retaining ring was found buried in the powdery aluminium oxides, confirming that the coupling was in fact the same as the others onboard.

But due to corrosion, the floating part was tightly seized on the hose barb shaft.

Investigation of the coupling from the other end of the hose showed no immediate signs of concern. However, there were some small pitting marks evident on the inside of the hose neck and removal of the rubber sleeve showed more indications of corrosion.

Attempts to free off the floating flange caused the fitting to fail.

It was also noted that corrosion was almost as advanced on this coupling as on the fitting which failed.

Actions

  • Examine existing fire hose couplings for corrosion, seized floating flanges, and any inability to rotate freely.
  • If replacement is required, ensure appropriate fittings are specified – brass may be preferred over aluminium.
  • Ensure planned maintenance systems cover appropriate detail for the inspection of fire hose fittings, with specific reference to examination for corrosion.
  • Ensure that all personnel involved in the day to day use and maintenance of fire hoses are briefed on the potential issue of electrolytic corrosion.

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