In-situ Corrosion Measurements of WWII Shipwrecks in Chuuk Lagoon, Quantification of Decay Mechanisms and Rates of Deterioration

Ian D Macleod

doi:10.3389/fmars.2016.00038

Abstract

This paper is based on a series of measurements taken on WWII historic shipwrecks that resulted from the effects of Operation Hailstone in February 1944 on the Japanese merchant fleet which was assembled in Chuuk lagoon, Federated States of Micronesia. More than 65 shipwrecks and 250 aircraft were sunk during two main bombing raids. The vessels lost covered a wide range of underwater orientation and water depths and so provided a perfect suite of corrosion experiments. Since the fuel on board the aircraft was either readily burnt at the time or was lost through volatilisation, the wrecked planes present no pollution problems today. However the bunker fuel kept inside on-board storage tanks does present a real conservation management crisis. In-situ measurements on many vessels have determined how water depth, the localised wreck topography, dissolved oxygen levels, temperature and salinity affects the corrosion rate of cast iron and mild steel. Thus corrosion rates can be calculated with confidence.

Highlights

The effects of Operation Hailstone in February 1944 were devastating for the residual Japanese merchant fleet which was assembled in Chuuk lagoon, Federated States of Micronesia
A series of in-situ corrosion studies on historic WWII shipwrecks and sunken aircraft in Chuuk Lagoon, Federated States of Micronesia, have been conducted over the past 14 years to determine the importance of water depth, aspect of the wrecks, the accumulation and periodic shedding of protective marine concretions on the overall rate of deterioration of the vessels
The studies by the museum teams has shown that the rate of decay of iron is logarithmically dependent on water depth for the first 20 m and the rate at which the corrosion rate falls becomes less dependent on depth owing to less flux of dissolved oxygen to the corroding interfaces

Summary

Introduction

The effects of Operation Hailstone in February 1944 were devastating for the residual Japanese merchant fleet which was assembled in Chuuk lagoon, Federated States of Micronesia. Many of the large naval vessels had left the area in response to rumors of an attack, more than 65 shipwrecks and 250 aircraft were sunk during two main bombing raids. The bunker fuel kept inside on-board storage tanks does present a real conservation management crisis that is increasingly significant. Sufficient information was obtained from these measurements to be able to determine how water depth, the localized wreck topography, dissolved oxygen levels, temperature and salinity affects the corrosion rate of cast iron and mild steel. Corrosion rates can Shipwreck Corrosion In-situ Measurements be calculated with confidence since the main parameters determining the rate of deterioration of the iron wrecks have been determined and the latent risk of oil leaking from the bunker fuel containers on board the shipwrecks can be assessed. Understanding the parameters that determine the corrosion rate of iron alloys in shallow tropical waters will provide valuable information for marine scientists dealing with the issues of unexploded ordnance by quantifying the decay rates of the shell casings

Methods

Findings

Conclusion