Nondestructive Evaluation to Quantify Marine Borer Attack: A New FPL Publication

shipworm_drawing

Drawing of a shipworm from a 1878 issue of Popular Science Monthly Volume 13, courtesy of Wikimedia Commons.

A new FPL publication explores a little-known topic of interest to those in seaside environments: Development of a Nondestructive Testing Technique to Quantify Deterioration from Marine Borer Attack in Sitka Spruce and Western Hemlock Logs: Observations from a Pilot Test.

FPL Research General Engineer Robert J. Ross along with John W. Forsman, Assistant Research Scientist, Michigan Technological University; John R. Erickson, Director (retired), FPL; and Allen M. Brackley, Research Forester, Pacific Northwest Research Station, conducted the pilot test reported here.

Stress-wave nondestructive evaluation (NDE) techniques are used widely in the forest products industry—from the grading of wood veneer to inspection of timber structures. Inspection professionals frequently use stress-wave NDE techniques to locate internal voids and decayed or deterio­rated areas in large timbers.

As these techniques grow in sophistication and application, practitioners are now applying them to ever more unique situations, for instance, for evaluating large timbers in Alaska, where NDE has the potential to be of value. In our largest state, all major population centers are located on the Pacific Ocean. Sawmills in the region often transport logs from harvest areas to mill loca­tion via waterways. Once at the mill, the logs may be stored for short periods of time in saltwater. These logs may be subject to deterioration from a variety of organisms, includ­ing decay fungi and marine borers.

Marine borers? These critters are molluscs or crustaceans that usually live in seas and they destroy wood by boring into and eating it. The gribble and shipworm are the best known as they penetrate any wood in favorable water.

severely-marine-borered

Severely deteriorated specimens. Note that nearly half the cross section shows visible signs of deterioration. NDE methods have the potential to provide sawmills with a method to identify logs that are deteriorated and are not suitable for production of a lumber product. Any NDE method that has the potential to better define the quality of logs and cants is of value to the industry.

In the pilot test explained in this new publication, Ross and others examined the relationship between stress-wave transmission time and the quality of wood in Sitka spruce and western hemlock logs that had varying degrees of deterioration as a consequence of attack from marine borers. Stress-wave transmission time, perpendicular to grain, was measured at several locations on each log. The logs were then sawn into lumber, which was then visually evaluated. A relationship was observed between stress-wave transmission time and deterioration of the logs and the yield of lumber from the logs.

Although these NDE techniques have proven useful, little information exists concerning the rela­tionship between stress-wave parameters and deterioration observed as a consequence of marine borer attack.

Because the results of this pilot study were encouraging, Ross and his colleagues recommend a larger study that would include a much larger sample and specimens from several sources.