Nondestructive Testing Technique to 

Quantify Deterioration from Marine Borer 

Attack in Sitka Spruce and Western 

Hemlock Logs

Observations from a Pilot Test Robert J. Ross

John W. Forsman

John R. Erickson

Allen M. Brackley

Research Note

FPL–RN–0333

United States Department of Agriculture

Forest 

Service

Forest Products

Laboratory

December

2014
December 2014

Ross, Robert J.; Forsman, John W.; Erickson, John R.; Brackley, Allen M. 

2014. 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 . Research Note FPL-RN-0333. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 3 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726–2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin. 

The use of trade or firm names in this publication is for reader information 

and does not imply endorsement by the United States Department of 

Agriculture (USDA) of any product or service.

The USDA prohibits discrimination in all its programs and activities on the 

basis of race, color, national origin, age, disability, and where applicable, 

sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part 

of an individual’s income is derived from any public assistance program. 

(Not all prohibited bases apply to all programs.) Persons with disabilities 

who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET 

Center at (202) 720–2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence 

Avenue, S.W., Washington, D.C. 20250–9410, or call (800) 795–3272 

(voice) or (202) 720–6382 (TDD). USDA is an equal opportunity provider 

and employer.

Abstract

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. Although these techniques have 

proven useful, little information exists concerning the relationship between stress-wave parameters and deterioration 

observed as a consequence of marine borer attack. In this 

pilot test, we 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. 

Keywords: Nondestructive testing, Sitka spruce, western 

hemlock, marine borer, stress waves

Acknowledgments

The authors gratefully acknowledge the financial support for 

this study provided by Mr. F.W. “Bill” Baxandall. This project was funded by the Federal Financial Assistance Grant 

No. PNW 03-DG-11261975-137.
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 

Robert J. Ross, Supervisory Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

John W. Forsman, Assistant Research Scientist

Michigan Technological University, Houghton, Michigan

John R. Erickson, Director (retired)

Forest Products Laboratory, Madison, Wisconsin

Allen M. Brackley, Research Forester

Pacific Northwest Research Station, Sitka, Alaska

Introduction

Nondestructive evaluation (NDE) has the potential to be of 

value in Alaska. Many of the major population centers in 

Alaska 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. 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.

Stress-wave nondestructive evaluation (NDE) techniques 

are used in the forest products industry—from the grading of wood veneer to inspection of timber structures. 

Inspection professionals use stress-wave NDE techniques 

to locate internal voids and decayed or deteriorated areas 

in large timbers. Although these techniques have proven 

useful, little information exists concerning the relationship 

between stress-wave parameters and deterioration observed 

as a consequence of marine borer attack in Sitka spruce and 

western hemlock logs. The pilot study summarized in this 

technical note was conducted to examine the potential for 

using stress-wave NDE techniques to identify deterioration 

in Sitka spruce and western hemlock logs.

Materials, Methods, and 

Observations

Seventeen Sitka spruce and 18 western hemlock logs were 

obtained from a local sawmill in Alaska and shipped to 

Michigan Technological University, Houghton, Michigan, 

for this pilot study. A commercially available stress-wave 

timing unit (Metriguard Model 239 A) was used to measure stress-wave transmission time, perpendicular to grain 

(perpendicular to a specimen’s fiber axis), at various points 

along each log specimen. A detailed description of the test 

setup and results obtained from its use are described in the 

references. A stress wave was induced by striking a specimen with a hammer instrumented with an accelerometer that 

emits a start signal to a timer. An additional accelerometer 

on the opposite side of the specimen sensed the leading edge 

of the propagating stress wave and sent a stop signal to the 

timer. The elapsed time for the stress wave to propagate 

between the accelerometers was recorded. This test was performed near the butt end of each log. The diameter of each 

log was determined, and the stress-wave transmission time 

(on a per-length basis, microseconds per foot) was calculated. Log diameters ranged from 12.8 to 23.5 in. (325 to 

597 mm). A visual assessment based on the presence of 

marine borer holes and visible deterioration from decay of 

each log was then completed. Figures 1–3 show typical log 

sections that have varying levels of deterioration. Log specimens with no visible evidence of marine borer or fungal 

attack were labeled as having no deterioration, specimens 

showing some visible evidence of attack were identified as 
Research Note FPL–RN–0333

2

being slightly deteriorated, and those with approximately 

one half of their cross section showing deterioration were 

labeled severely deteriorated. 

Each log was then sawn into lumber. A visual assessment of 

each lumber specimen was completed, and an estimate of 

lumber yield (based on a Decimal C scale) calculated. This 

was accomplished using accepted visual grading criteria. 

Tables 1–3 summarize results obtained from our tests of Sitka spruce and western hemlock logs. Note that stress-wave 

times increased with the presence of deterioration for logs 

from both species. This is in close agreement with results 

observed in other studies. 

Conclusions and Recommendation

Based on the results of this study, we conclude the 

following:

1. Stress-wave transmission times in Sitka spruce and western hemlock logs, measured across the grain, are affected 

by the presence of deteriorated wood from marine borer 

and decay attack. 

2. Sitka spruce and western hemlock logs having elevated 

stress-wave transmission times yield significantly lower 

volumes of usable lumber.

Because these results are encouraging, we recommend 

a larger study on the strength of the relationship. Such a 

study should include a much larger sample than that used in 

the study reported here as well as specimens from several 

sources.

Additional Information

Brashaw, Brian K.; Vatalaro, Robert J.; Wacker, James P.; 

Ross, Robert J. 2005. Condition assessment of timber bridges. 2, Evaluation of several stress-wave tools. Gen. Tech. 

Rep. FPL-GTR-160. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 11 p.

De Groot, R.; Ross, R.; Nelson, W. 1994. Nondestructive 

assessment of biodegradation in southern pine sapwood 

exposed to attack by natural populations of decay fungi 

and subterranean termites. Proceedings, twenty-fifth annual 

meeting, The International Research Group on Wood Preservation, Bali, Indonesia, May 29–June 3, 1994. 13 p.

De Groot, R.C.; Ross, R.J.; Nelson, W.J. 1995. Natural progression of decay in unrestrained, southern pine sapwood 

lumber exposed above ground. Proceedings, twenty sixth 

annual meeting, IRG, Helsinger, Denmark. June 11–16, 

1995.

De Groot, R.C.; Ross, R.J.; Nelson, W.J. 1998. Nondestructive assessment of wood decay and termite attack in southern pine sapwood. Wood Protection 3(2):25–34.

Illman, B.L.; Yang, V.W.; Ross, R.J.; Nelson, W.J. 2002. 

Nondestructive evaluation of oriented strand board exposed 

to decay fungi. In: Proceedings, 33rd annual meeting of The 

International Research Group on Wood Preservation, Cardiff, United Kingdom. May 12–17, 2002. Stockholm, Sweden: IRG Secretariat, 2002. IRG/WP; 02-20243: 6 p.

Pellerin, R.F.; DeGroot, R.C.; Esenther, G.R. 1985. Nondestructive stress wave measurements of decay and termite 

attack in experimental wood units. In: Proceedings, 5th 

nondestructive testing of wood symposium, 1985 September 

9–11; Pullman, WA. Pullman, WA: Washington State University: 319–353.

Pellerin, R.F.; Ross, R.J. 2002. Nondestructive evaluation of 

wood. Forest Products Society, Madison, WI. 210 p.

Reinprecht, L.; Hibky, M. 2011. The type and degree of 

decay in spruce wood analyzed by the ultrasonic method in 

three anatomical directions. Bioresources. 6(4):4953–4968.

Ross, R.J.; Pellerin, R.F. 1988. NDE of wood-based composites with longitudinal stress waves. Forest Products Journal. 38(5): 39–45.

Ross, R.J.; De Groot, R.C.; Nelson, W.J. 1994. Technique 

for nondestructive evaluation of biologically degraded 

wood. Experimental Techniques. 18(5): 29–32.

Ross, R.J.; De Groot, R.C.; Nelson, W.J.; Lebow, P.K. 1996. 

Assessment of the strength of biologically degraded wood 

by stress wave NDE. Proceedings, seventh international 

symposium on durability of building materials and components, Volume 1. C. Sjostrom, ed., E&FN Spon, 2-6 Boundary Row, London SE1 8HN, UK: 637–644.

Ross, R.J.; De Groot, R.C.; Nelson, W.J.; Lebow, P.K. 1997. 

Relationship between stress wave transmission characteristics and the compressive strength of biologically degraded 

wood. Forest Products Journal. 47(5):89–93.

Ross, R.J.; De Groot, R.C. 1998. Scanning technique for 

identifying biologically degraded areas in wood members. 

Experimental Techniques. 22(3):32–33.

Ross, R.J.; Volny, N.; Pellerin, R.F.; Salsig, W.W.; Falk, 

R.H. 1999. Inspection of timber bridges with stress wave 

nondestructive evaluation tools. A guide for use and interpretation. FPL–GTR–114. U.S. Department of Agriculture, 

Forest Service, Forest Products Laboratory, Madison, WI.

Ross, Robert J.; Pellerin, Roy F.; Volny, Norbert; Salsig, 

William W.; Falk, Robert H. 1999. Inspection of timber 

bridges using stress wave timing nondestructive evaluation 

tools—A guide for use and interpretation Gen. Tech. Rep. 

FPL–GTR–114. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 15 p.
Development of a Nondestructive Testing Technique to Quantify Deterioration from Marine Borer Attack 

3

Ross, R.J.; Yang, V.W.; Illman, B.L.; Nelson, W.J. 2003. 

Relationship between stress wave transmission time and 

bending strength of deteriorated oriented strandboard. Forest 

Products Journal. 53(3):33–35.

Ross, R.J.; B.K. Brashaw; X. Wang; R.H. White; R.F. Pellerin. 2004. Wood and timber condition assessment manual. 

Forest Products Society, Madison, WI. 73 p. 

Ross, R.J.; X. Wang; B.K. Brashaw. 2005. Detecting decay 

in wood components. In: Inspection and monitoring techniques for bridges and civil structures, Woodhead Publishing Limited, Cambridge, England: 100–114.

Ross, R.J.; Dundar, T. 2012. Condition assessment of 2500 

year old wood coffin. Res. Note. FPL–RN–0327. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory. 3 p. 

Wang, X.; Divos, F.; Pilon, C.; Brashaw, B.K.; Ross, R.J.; 

Pellerin, R.F. 2004. Assessment of decay in standing timber 

using stress-wave timing nondestructive evaluation tools. A 

guide for use and interpretation. U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, General 

Technical Report, FPL–GTR–147; Madison, WI. 12 p.

White, R.H.; Ross, R.J. 2014. Wood and timber condition 

assessment manual–second edition. Gen. Tech. Rep. 

FPL–GTR–234. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 

93 p.

Figure 1—Specimens showing no visual indication of 

deterioration.

Figure 2—These specimens were labeled as slightly deteriorated. Note visual evidence of marine borer attack.

Figure 3—Severely deteriorated specimens. Note that 

nearly half the cross section shows visible signs of 

deterioration. 
Research Note FPL–RN–0333

4

Table 1—Stress-wave transmission times of Sitka spruce and western hemlock logs perpendicular to stem 

(μsec/ft).

Species 

Sitka spruce Western hemlock 

None Slight Heavy None Slight Heavy 

Visual deterioration 1 2 1 2 1 2 1 2 1 2 1 2 

Readings (μs/ft) 202 251 247 309 545 241 393 362 336 336 

223 221 243 295 594 328 271 258 253 289 256 255 

223 240 228 229 457 236 217 207 213 212 627 1,075 

264 272 222 230 372 357 300 305 249 216 335 377 

355 210 205 230 246 273 269 252 309 309 263 323 

199 196 217 235 348 247 341 235 332 315 

Average 237 236 372 265 282 403 

Standard deviation 45 22 117 39 59 223 

Minimum 196 205 236 207 212 255 

Maximum 355 295 594 348 393 1,075 

Table 2—Average stress wave times of Sitka spruce and western 

hemlock logs, perpendicular to stem (μsec/ft). 

Species Visual deterioration 

Stress wave transmission time 

 (μs/ft) 

Average (Min, max) 

Sitka spruce None 

Slight

Heavy 

237

236

372

(196, 355) 

(205, 295) 

(236, 594) 

Western 

hemlock 

None

Slight

Heavy 

265

282

403

(207, 348) 

(212, 393) 

(255, 1075) 

Table 3—Comparison between Decimal C scale stick predicted lumber yield and 

measured for sound, slightly deteriorated and heavily deteriorated Alaskan western 

hemlock and Sitka Spruce. 

Species Condition 

Number 

of logs 

Average 

log

diameter 

(in. (mm)) 

Potential lumber yield 

(%)

Decimal C 

scale Measured Yield 

Sitka spruce Sound 6 18.6 (472) 103 113 109 

Slight deterioration 6 15.7 (399) 78 80 102 

Heavy deterioration 5 17.3 (439) 87 68 78 

Western 

hemlock 

Sound 6 17.4 (442) 106 96 90 

Slight deterioration 6 17.6 (447) 99 77 77 

Heavy deterioration 6 16.9 ( 429) 90 35 39