A $3 Item...A $90,000 Loss
A $3 Item...A $90,000 Loss
By: Zdenek Trnka, PE, TRNKA Engineers, I-ENG-A Member Seattle
Let’s see now….hmmmm? That works out to odds of 30,000 to 1. A ratio of 30,000:1 is much better than the average lotto odds but not so great for the insurer. When someone, somewhere, uses an incorrect pipe fitting costing $3 and the use of the incorrect fitting results in $90,000 damages it is surely not a happy day.
In this case the incorrect pipe fitting cost only $3 dollars. As it happens, the correct pipe fitting also would cost only about $3. Both pipe fittings look very similar, either as common ordinary brass or bronze. The reason for use of the incorrect fitting is unknown but not likely related to the cost of the fitting since both cost about the same. Most probably the use of the incorrect fitting was a simple matter of inexperience on the part of the person doing the installation of the sea strainer. What does matter is where and how the fitting was used.
The background to this 30,000 to 1 loss has to do with a $1,000,000 sailing yacht. This very nice yacht has an auxiliary motor for times of non-sail propulsion. This auxiliary motor is cooled by seawater that is drawn into the engine cooling system through a sea strainer. Mounted next to the outer hull of the vessel and below the water line, a failure of the sea strainer that allows water to enter unrestricted could cause the yacht to flood or even sink. In this event a pipe fitting broke away from the sea strainer thus allowing water to enter the vessel. The vessel consequently flooded resulting in $90,000 in damages to pumps, motors and other equipment located in the bilge area of the vessel.
Our assignment at Trnka Engineers Co. was to determine the cause of the fitting failure. The cause of the failure could possibly provide the basis for subrogation of the claim. The evidence, the sea strainer and pipe fitting, was provided to us by the adjuster as seen in Photo P-1. The broken fitting location is indicated by the red arrow.
A quick 10x magnification inspection of the broken pipe fitting gave us cause to suspect that a brass pipe fitting was used in the sea water cooling system where bronze, a more appropriate pipe fitting material, should have been used.
There are many copper based alloys, however, only a few are suitable for extended exposure to salt water. Copper alloys with relatively high zinc content when exposed to salt water will succumb to a phenomenon termed “selective leaching” or otherwise known as “dezincification”. The phenomenon in this case is that the zinc, in constant contact with salt water, goes into solution with the sea water and over time leaches out of the pipe fitting. As one would easily conclude the zinc eventually dissolves out of the pipe fitting leaving only the copper base material along with some trace elements. This remaining material is very brittle and fractures easily as occurred in this situation.
A closer view is seen in the Photos P-2 and P-3. Note the “spongy” appearance of the fractured pipe fitting surface in Photo P-3. The spongy appearance occurs with the migration of the zinc out of the copper base material of the pipe fitting.
Sufficiently certain of our suspicion of the cause and origin of the failure of this pipe fitting we employed the services of a competent laboratory to complete a chemical analysis of the pipe fitting and sea strainer body.
The laboratory findings did indeed confirm the fitting to be brass and dezincification did occur as a result of exposure to sea water. This finding was then reported to the adjuster who now had opportunity to subrogate back to the yacht builder.