Investigation of the Use of

Nondestructive Methods for

Inspection of Seams of

Single-Ply Roofing Membranes

NBSIR 86-3455

Walter J. Rossiter, Jr.

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

September 1986

'^"'pared for: val Civil Engineering Laboratory

QC rt Hueneme, CA 93043-5003

100

.056

NO.86-3455

1986

NBSIR 86-3455

INVESTIGATION OF THE USE OF

NONDESTRUCTIVE METHODS FOR

INSPECTION OF SEAMS OF

SINGLE-PLY ROOFING MEMBRANES

Walter J. Rossiter, Jr.

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

September 1986

Prepared for: Naval Civil Engineering Laboratory

Port Hueneme, CA 93043-5003

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

ABSTRACT

Investigations were conducted regarding the use of the ultrasonic

pulse echo and the infrared thermography nondestructive evaluation

(NDE) methods for detecting voids and delaminations in adhesivebonded seams of single-ply roofing membranes. Previous studies

had indicated that these defects could be detected using the two

NDE methods. In the present study, voids incorporated in

1.2 m (48 in.) long seam test specimens were located by the

pulse-echo method using a wheel transducer to scan along the

length of the seam. These results indicated that the ultrasonic

pulse echo method using a wheel transducer can be useful as a field technique for assisting in the quality assessment of

seams .

When using the infrared thermography method to evaluate the seam

specimens, it was found that, unlike previous studies, only

sections of some voids were detected and that other voids were

not detected at all. It was suggested that collapse of the voids

due to the applied pressure during seam formation might have

provided insufficient surface temperature differential between

the bonded areas of the seam and the void areas of the seams

during transient heat flow. The results raised concerns that the

infrared thermography method may not be practical for the general

detection of voids of seams in service.

Key words: adhesive bonds; detection; infrared thermography;

membranes; nondestructive evaluation; roofing; seams;

single-ply; ultrasonic pulse echo; voids.

i i i
TABLE OF CONTENTS

Page

ABSTRACT Hi

1. INTRODUCTION 1 1.1 Background 2

1.2 Objective and Scope 3

2. EXPERIMENTAL 5

2.1 NDE Methods 5

2.2 Seam Fabrication 7

3. RESULTS AND DISCUSSION 10

3.1 Large-Sized Membrane Specimens 10

3.2 Small-Sized Membrane Specimens 16

4. SUMMARY AND RECOMMENDATIONS 18

5. ACKNOWLEDGEMENTS 21

6. REFERENCES 22
LIST OF TABLES

Page

Table 1. Membrane Materials Included in the Study 24

Table 2. Results of NDE Inspections of Large-Sized

Membrane Specimens 25

Table 3. Results of NDE Inspections of Small-Sized

Membrane Specimens 26

LIST OF FIGURES

Page

Figure 1. Diagram of the 1.2 m (48 in.) Large-Sized

Test Specimen Indicating the Voids

Incorporated in the Seam 27

Figure 2. Plan of the Chamber Test Specimen 28

Figure 3. Types of Voids in Lap Seams 29

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1. INTRODUCTION

Durable, single-ply roofing membranes are characterized, among

other factors, as having seams that remain watertight over the

intended service life of the roofing. Failure of a seam can

result in water penetration of the roofing system causing damage

to itself, other building components, and building contents, and

also loss of thermal efficiency of the roof insulation. In spite

of the importance of having long-lasting, watertight seams, the

quality of those fabricated in the field is usually only assessed

at the time of roofing construction by visual observation, and by

manual inspection of the lap edge to ascertain that the seam is

bonded at that location.

Nondestructive evaluation (NDE) procedures are not presently

available to assure that bond formation is complete in all

sections of the seam. The development of NDE methods would be

beneficial for a number of reasons. They have the potential of

providing a quality control technique for examining the completeness of adhesive application and the resultant bond formation

during the formation of seams in the field. In addition, NDE

methods could be used to investigate the extent of disbonding, if

such a problem were to arise during service. Also, such methods

could assist in obtaining knowledge on adhesive-bond performance.

For example, environmental conditions leading to loss of adhesivebonds during service, or growth of voids within seams could be

investigated without destruction of the seams.

1
1.1 Background

The use of NDE methods for detecting voids and delaminations in

adhesive-bonded seams of single-ply roofing membranes has been

under preliminary investigation at the U.S. National Bureau of

Standards (NBS) [1,2]. Voids may be incorporated in seams at the

time of fabrication due to lack of total adhesive coverage on sections of the sheets to be bonded. Delaminations may occur

through disbonding after seam fabrication. The previous NBS

studies have reported on the potential for using the ultrasonic

pulse echo method and the infrared thermography method as a means

of detecting the presence of the defects in the interior portions

of the seams where visual inspection is impossible. Factors that

may affect instrument response, such as pressure applied during

seam fabrication, void size, water in the void, and type of

substrate under the seam, have been investigated [2]. Both the

ultrasonic pulse echo and the infrared thermography methods have

had considerable application to the detection of defects in

building components, composites, and seams of membranes [3-11].

The results of the previous NBS studies [1,2] indicated that,

under laboratory conditions, both NDE methods were successful in

locating the presence of hidden voids in seam specimens.

Nevertheless, it was also found that, as conducted in the

laboratory, each NDE technique had certain limitations that

could adversely affect its practical use in the field in locating

voids and delaminations in seams. In particular, the ultrasonic

2
pulse echo method could not detect voids filled with water,

and produced false indicators that were dependent on the pressure

applied to the transducer during testing. The ultrasonic pulse

echo method, as used in the laboratory in the preliminary

studies, was considered impractical to use in field applications

for scanning large expanses of seams due to the small size (about

19 mm or 0.75 in. diameter) of the transducer. The infrared

thermography method had limitations dealing with uniform,

controlled heating of the sections of seams using a laboratory

hot air blower, and the practicality of using the hot air blower

in the field on large expanses of seams under variable environmental

conditions

1.2 Objective and Scope

This paper presents further results of studies to investigate the

feasibility of using the NDE techniques for detecting voids and

delaminations in seams of single-ply membranes. The objective

was to explore improvements in the NDE techniques that could

result in increased potential for their use in the field. In the

case of the ultrasonic pulse echo method, the principal factor

investigated was the use of a wheel transducer that could scan

long expanses of seams quickly and at constant pressure. In the

case of the infrared thermography method, the primary factor

investigated was the potential use of sunlight (absorbed solar

radiation) as the source of transient heat flow in the seam.

3
Since the previous NBS studies [1,2] were limited to seams

fabricated from black EPDM (ethylene propylene diene terpolymer)

rubber, the use of the NDE methods for detecting voids incorporated

in seams of other single-ply membrane materials was explored.

The ultrasonic pulse echo and the infrared thermography methods

are, in principal, applicable to seams of elastomeric, thermoplastic,

and polymer-modified bitumens [1,2]. However, laboratory tests

have not been conducted on all these types of single-ply membrane

materials. The additional materials investigated in the present

study were white EPDM, white chlorosulfonated polyethylene

(CSME), and styrene-butadiene-styrene (SBS) modified bitumen.

4
2. EXPERIMENTAL

2.1 NDE Methods

A description of the ultrasonic pulse echo and infrared thermography

methods used in the study has been given previously [1,2]. Only

a brief summary of the methods is given here.

2.1.1 The Ultrasonic Pulse Echo Method

In this method, ultrasonic waves are transmitted into the

test specimen (e.g., single-ply membrane seam) and are reflected

off discontinuities and at interfaces. The time required for the

reflected signal (echo) to be detected is dependent on the

distance it travels and the speed of the pulse in the test

material. An echo associated with a completely bonded seam would

pass through two membrane layers. If the area of the seam under

inspection contained a void, the echo would pass through one

layer of membrane. Thus, twice as much time is required for the

echo to pass through a completely bonded seam than through the

unbonded (void) area.

Two piezoelectric transducers of different frequencies were

included in the present study, depending on the test specimen

being inspected. In the case of large-sized (see section

2.2.1) specimens having 6 voids, a wheel transducer operating at

2.25 MHz was selected. The ultrasonic beam was generated normal

to the surface of the test specimen and effectively scanned an

area 25 mm (1 in.) in diameter. For the small-sized specimens

5
(see section 2.2.2) having two voids, a hand-held transducer with

a frequency of 1.0 MHz was used. Water was usually the coupling

medium between the specimen surface and both transducers,

although in some tests, a petroleum-based lubricating oil was

used .

The wheel transducer was mounted on a rolling platform having

three wheels. In this manner, the entire length of a test

specimen could be inspected by pushing the platform holding the

transducer along the specimen surface. The mass of the wheel

transducer and platform was about 4.8 kg (10.6 Ibm).

2.1.2 The Infrared Thermography Method

If transient heat flow occurs in a material (e.g., a seam in

a membrane), the presence of voids or delaminations in it may

cause the surface temperature directly above the defect to be at

a different temperature than that of a defect-free region.

Measurement of the temperature differential using the infrared

camera can be used to detect the presence of the defect. The

infrared camera used in the present study could detect surface

temperature differentials of 0.2 ®C (0.4 ®F).

Transient heat flow was normally induced in the seam by heating

its surface with a laboratory hot air blower. In some tests (see

section 3.2.1), heat lamps were used to heat the membrane

6
specimen which was then allowed to cool under ambient conditions

or by blowing unheated laboratory air across its surface.

2.2 Seam Fabrication

Seams were fabricated from sheets of the single-ply membrane

materials (nos. 1-4) listed in table 1. In the case of the nonbituminous specimens (nos. 1-3), the sheets were cleaned with

solvents as recommended by the material manufacturers and contact

adhesives were applied in accordance with the manufacturers'

instructions. The cleaning solvent for the black EPDM was a proprietary product provided by the manufacturer. The seam of

the SBS-modified bitumen (no. 4) was prepared using hot asphalt

as the adhesive.

Voids of known size were incorporated in the seams by placing

masking tape having the desired shape and area on both membrane

material surfaces prior to application of the adhesive. The

masking tape was removed prior to joining the membrane sheets

together for seam formation.

2.2.1 Large-Sized Membrane Specimens

Large-sized membrane specimens having 76 mm (3 in.) wide seams

were fabricated from the black EPDM rubber. The length of the

specimens was 1.2 m (48 in.) and the width was a minimum of 0.3 m

(12 in.). Six (6) voids of different size and shape were

7
incorporated in the seams, as shown in Figure 1. In the fabrication of the large-sized specimens, pressure was applied to the

newly-formed seams using a hand roller typical of those employed

in the field. The pressure exerted in the process has been

2 measured to be, on the average, 0.7 MPa (100 Ibf/in ) [2].

Two types of large-sized membrane specimens were fabricated. For

the first type, the specimen consisted only of the rubber sheet

with the fabricated seam; that is, the membrane was not mounted

on or adhered to any substrate. This specimen could then be

placed on any desired substrate during the NDE measurements.

This specimen is referred to as the "seam alone" specimen in the

present report.

For the second type of large-sized specimen, the seams having

voids were included in a 1.2 x 1.2 m (48 x 48 in.) roofing system

specimen consisting of membrane, insulation, and deck, as described in Figure 2. The insulation boards were mechanically

fastened to the wooden deck, and the EPDM membrane was totally

adhered to the fiberboard insulation layer. As evident from

Figure 2, the roof system specimen had three seams that were

spaced equidi stantly across the surface, and that were located

above joints in insulation boards. However, for the present

study, only one of the three seams was used for the NDE detection

of voids. This specimen was constructed in a chamber having a

bank of heat lamps mounted above the membrane to enable heating

8
of the specimen surface. This specimen is referred to as

the "chamber specimen" in the present report.

2.2.2 Small-Sized Membrane Specimens

With the exception of the black EPDM (no. 1), the small-sized

specimens were approximately 270 x 200 mm (10.5 x 7.8 in.) and

contained a 76 mm (3 in.) lap seam centered parallel to the long

dimension. The seams of each of these specimens contained

two voids that were 44 mm (1.8 in.) in diameter. The black EPDM

specimen was about one half the size of the others, and contained

only one void in the seam. In the fabrication of the small-sized

specimens, uniform pressure was applied to the newly-formed seams

by placing them in a laboratory press for 4-5 seconds under about

0.50 MPa (75 Ibf/in^).

9
3. RESULTS AND DISCUSSION

3.1 Large-Sized Membrane Specimens

3.1.1. Ultrasonic Pulse Echo Method

The ultrasonic pulse echo method using the wheel transducer with

water as the coupling medium was applied to the large-sized

membrane specimens. All voids in the seams were detected for

both the seam alone specimen and for the chamber specimen (Table

2). The seam alone specimen was placed on either a laboratory

bench or on top of the EPDM membrane of the chamber specimen

during the NDE evaluation.

In the tests using the wheel transducer, the echo pattern

observed when the transducer was placed on bonded sections of the

seam was complex and difficult to interpret because of the number

of signals produced. When the wheel transducer was placed on a void, the echo pattern was also complex, but contained a unique

signal that was not present in the echo pattern of the bonded

area of the seam. This unique signal was used to indicate the

presence of a void. The wheel transducer was rapidly scanned

along the 1.2 m (48 in.) length of the specimen, and each of the

six voids was located by the appearance of the unique signal in

the echo pattern. An audio alarm, which sounded whenever the

unique echo signal was produced, was also used to indicate the

presence of the voids when the wheel transducer was pushed over

the surface of the specimens. These results indicated that the

10
use of wheel transducers may have applicability for examining

long expanses of seams of roofs in service.

Unlike detecting voids using a small transducer which is manually

scanned across the specimen surface, false indicators of apparent

voids in bonded sections of the seam were not produced using the

wheel transducer technique. The stability and mass of the

rolling platform on which the transducer was mounted provided

constant load and uniform contact of the transducer with the

membrane specimen surface.

3.1.2 Infrared Thermography Method

The infrared thermography method was applied to detection of

voids in the seams of the large-sized membrane specimens by using

a hot air blower or heat lamps as the source of transient heat

flow. During these tests, the seam alone specimen was placed on

top of the chamber specimen under the heat lamps. The results of

the tests are summarized in Table 2. The results indicated that,

for the most part, the voids were only detected in part or not

detected at all. Only void no. 2 of the chamber specimen was

found to be entirely visible. These findings were in contrast

with those of previous studies [1,2] and the results for smallsized specimens in the present study (see section 3.2.2) wherein

voids greater than 6 mm (0.2 in.) in diameter were detected

using the infrared thermography method.

11
In the present study, in those cases where the voids were only

detected In part, the perimeters of their geometric shapes were

the main features observed in the thermographic images. The

center portions of the void images displayed the same infrared

image color contrast as the bonded portion of the specimen. This

suggested that, during the NDE examination, transient heat flow

through the center portion of the void was comparable to that

occurring in the bonded sections of the seam. As a consequence,

the surface temperature above the center portion of the void

would not differ significantly from that above the bonded areas.

A temperature differential is necessary to allow detection of the

void using the infrared thermography technique. Lack of a temperature differential might be expected to occur if the

two rubber sheets comprising the seam were in contact at the

center portion of the void. In effect, a collapse of the

incorporated void might have occurred. Figure 3, for example,

depicts two seams with voids: the first having the rubber sheets

totally separated at the void, and the second having the sheets

I in contact at the center portion of the void.

As previously indicated, pressure was applied to the large-sized

specimens during seam formation using a hand roller. It may be

possible that, using the roller, the sheets of rubber at the

center portion of the voids were pushed together, since the

roller technique exerts pressure over a relatively small area of

the specimen. The effect of pushing the rubber sheets together

12
at the center portion of the voids is to create small defect

areas (at the void perimeter) which are observed using the

infrared thermography method (Figure 3B). It might be expected

that some gap defect would be present at the perimeter of the

collapsed void because of the adhesive layer at that location.

In those cases where the voids were not detected at all, it was

considered that not only might the rubber sheets at the center of

the voids have been in contact, but also the remaining gaps at

the void perimeters were too small to be detectable using the

infrared thermography method. Theoretical considerations have

shown that the width of a hidden defect should be about twice the

thickness of the layer covering the defect in order that it may

be detected using the infrared thermography method [12].

Previous investigations at NBS have shown that a round void, 3 mm

(0.13 in.) in diameter and fabricated from EPDM sheets of 1.5 mm

(0.06 in.) thickness, was not detected using the infrared

thermography method [2].

The possible effect of the collapsing of voids precluding their

detection using the infrared thermography method was not investigated

in the present study, and should be the subject of further

study. Such an investigation should involve mathematical

analysis to predict seam surface temperatures as a function of

void configuration, and laboratory study of specimens prepared

based on the results of the analysis. A question regarding the

13
collapse of the voids under the load of the hand roller is why

the EPDM rubber sheets did not separate after release of the

roller pressure. A possible explanation is that the rubber

sheets, freshly cleaned with solvent and then pushed together,

developed sufficient bond at the void to be held in contact

during the course of the experiment.

In considering reasons why voids in seams of the large-sized

specimens were not detected using the infrared thermography

method, the question was raised as to whether void thickness had

an effect. To examine such a possibility, two EPDM seam specimens

having uniform adhesive-layer thickness and incorporated voids

were prepared. In this case, a laboratory press was used to

apply pressure during bond formation. One specimen was fabricated

using two-sided cellulose adhesive tape with a thickness of about

0.08 mm (0.003 in.). The second was made using two-sided EPDMseaming tape with a thickness of about 0.7 mm (0.03 in.). The

thicknesses of the two specimens bracketed the range of adhesive

thickness normally encountered when contact adhesives are applied

to EPDM with a brush or a roller. When examined using the

infrared thermography method, the voids in the two specimens were

detected. It was also subjectively observed that the thicker

adhesive layer provided a stronger thermal image of the voids

than that given by the thin layer.

14
The fact that all voids intentionally incorporated in seams

were not detected in the present study using the infrared

thermography method indicates that the technique may not be

useful for general investigation of voids and delaminations in

seams in service. Final judgment on this point should be

reserved until the results of studies on the effect of void

collapse are completed.

As mentioned in the introduction, an intent of preparing the

chamber specimen was to investigate the possibility of using heat

lamps, as simulated solar radiation, for providing the source of

transient heat flow. In the laboratory test, the lamps were used

to heat the membrane. When the lamps were shut off, the specimen

cooled during which time the surface of the seam was scanned with

the infrared camera. (Although the experiment was not conducted,

it was envisioned that, in the field, cooling of a solar heated

membrane might be brought about by briefly casting a shadow,

e.g., using an umbrella, on the seam section under examination.)

As given in Table 2, void no. 2 of the chamber specimen was

detected using heat lamps as the source of transient heat flow,

when unheated air was blown across the seam surface after the

lamps were shut off. This result suggested that (assuming void

collapse is not an issue) use of solar heating of seams on roofs

as a source of transient heat flow may be practical, provided

that air movement across the solar heated surface is implemented

along with casting a shadow on the seam. Nevertheless, until the

15
issue regarding void collapse is resolved, further investigation

on solar heating as a source of transient heat flow is not

considered warranted.

3.2 Small-Sized Membrane Specimens

3.2.1 Ultrasonic Pulse Echo Method

The voids in the small-sized membrane specimens (nos. 1-4) were

detected using the ultrasonic pulse echo method, as given in

Table 3. As was found in previous studies in this laboratory

[1,2], void detection was sensitive to the pressure applied to

the transducer. Pressure on the transducer varied in these

measurements, since the transducer was manually scanned over the

surface of the membrane specimen. False indicators of the

presence of voids would appear if the transducer was not kept in

uniform contact with the membrane specimen surface. The CSME and

the SBS-modified bitumen membrane specimens (nos. 3 & 4, respectively)

appeared to be more sensitive to the applied pressure than the

EPDM specimens. This was attributed to the non-planar nature of

the surfaces. The CSME specimen was slightly embossed because of

the reinforcement within the sheet. The SBS-modified bitumen was

surfaced with mineral granules.

The mineral granule surfacing on the SBS-modified bitumen

precluded the use of water as a transducer coupling medium for

this specimen. When used as a coupling medium, the water ran

between the granules and from the specimen surface with loss of

16
coupling. A general purpose, petroleum-based, lubricating

oil was found to be satisfactory as a coupling medium during the

test. However, a general note of caution should be mentioned

regarding the use of oils with roofing membrane materials. Some

oils and membrane materials may not be compatible, and damage to

the membrane material may result due to application of oil on the

surface

3.2.2 Infrared Thermography Method

The results of the NDE inspection of the small-sized membrane

specimens using infrared thermography are summarized in Table 3.

Voids were detected in seams of the four types of membrane

specimens when they were heated using the hot air blower, and

also when the heated membrane specimens were cooled by blowing

unheated air across the surfaces. It is noted that void collapse

with the small-sized specimens might not be expected to have

occurred, since pressure during seam formation was applied

uniformly across the seam surface using a laboratory press.

As is given in Table 3, the length of time during which the void

image remained visible after heating ceased varied among the four

types of specimens. This was presumably due to factors such as differences in adhesive thickness and in thermal properties of

the membrane materials, which resulted in the various specimens

achieving a uniform surface temperature at different rates. An

evaluation of the thermal properties of the different membrane

materials included in the study and their effect on void detection

was beyond the scope of the present study.

17
4. SUMMARY AND RECOMMENDATIONS

Investigations were made regarding the use of the ultrasonic

pulse echo and the infrared thermography NDE methods for detecting

voids and delaminations in adhesive- bonded seams of si ng 1 e -ply

roofing membranes. Previous laboratory work at NBS indicated

that both techniques offered the possibility for locating defects

in the hidden interior portions of seams of single-ply membranes.

However, further investigation was needed before the techniques

would be applicable to field use.

In the present study, the principal factor investigated regarding

the ultrasonic pulse echo method was the use of a wheel transducer that could possibly scan long expanses of seams quickly and

at constant pressure. A wheel transducer was mounted on a rolling platform and used to detect the presence of six voids in

1.2 m (48 in.) long EPDM specimens. All voids were readily

located as the transducer was scanned along the length of the

seam, providing evidence that the ultrasonic pulse echo method

using a wheel transducer can be useful as a field technique for

assisting in the quality assessment of seams. False indicators

of the presence of voids in bonded areas of seams were not

observed during the testing with the wheel transducer. The wheel

transducer was not investigated for field use.

In the case of the infrared thermography method, the primary

factor investigated was the potential use of sunlight (absorbed

18
solar radiation) as the source of transient heat flow in the

seam. It was found that some voids incorporated intentionally

in the seams were only detected in part and that other voids

were not detected at all. It was postulated that collapse of the

voids under the pressure applied by the roller during seam

fabrication resulted in contact of the rubber sheets in the

center portion of the voids. This collapse produced insufficient

surface temperature differential between the bonded areas of the

seam and the void areas of the seams during transient heat flow.

The present results raise concerns that the infrared thermography

method may not be practical for the general detection of voids

and delaminations of seams in service. It is suggested that

final judgment on the utility of the infrared thermography method

be reserved until the further investigations of the void collapse

effect are carried out.

In the present study, the ultrasonic pulse echo and the infrared

thermography methods were also applied to seam specimens fabricated

from white EPDM, white ch 1 orosu If onated polyethylene (CSME), and

styrene-butadiene-styrene (SBS) modified bitumen. These tests

were included since the previous studies were limited to seams

fabricated from black EPDM rubber. Voids incorporated in seams

of these membrane materials were detected using both NDE methods,

demonstrating their potentially wide applicability to different

types of elastomeric, thermoplastic, and po 1 ymer -mod i f i ed bitumens.

19
Based on the results of the present study, it is recommended

that:

1) Investigation into the use of the ultrasonic pulse echo

method be continued to study field use of wheel transducers

for detecting voids in seams in service. A key item to be

included should be the development of equipment for use in

the field.

2) Investigation of the possible effect of void collapse on the

capability of the infrared thermography method to detect

hidden voids in seams be conducted. The investigation

should include a mathematical analysis of seam surface

temperatures as related to void configuration and laboratory

testing based on the results of such analysis.

20
5. ACKNOWLEDGEMENTS

This study was sponsored by the Naval Civil Engineering Laboratory

(NCEL), Port Hueneme, California. The author expresses his

appreciation to Dr. Robert Alumbaugh (NCEL) for his assistance in

the development of the study, and for his support and encouragement

throughout its course.

The author expresses appreciation and thanks to his NBS colleagues

for their assistance in conducting the study. Mr. Dale Bentz,

Mr. Edward Embree, Mr. Jessie Hairston, Mr. Jack Lee, and

Mr. James Seiler contributed to the preparation of test specimens

and the NDE evaluations. Special thanks are expressed to

Dr. Gerald Blessing who assisted in the ultrasonic pulse echo

measurements, and provided many valuable suggestions regarding

the application of the method to detecting voids in seams of

single-ply membranes. The assistance of Mr. Joseph Monroe,

Eastern NDT (Hopewell, Va.) in providing use of the wheel

transducer for the study is also acknowledged with thanks.

21
6 . REFERENCES

1. Clifton, J.R., Pizzutti Dos Santos, J., and Rossiter, W.J.,

Jr., "Non-Destructive Evaluation Methods for Assessing the

Quality of Seams in Single-Ply Membranes," Proceedings, 2nd

International Symposium on Roofing Technology, National

Roofing Contractors Association, Chicago, IL (September

1985), pp. 433-437.

2. Rossiter, W.J., Jr. and Clifton, J.R., "The Use of Nondestructive

Methods for Inspection of Single-Ply Roofing Membranes,"

Durability of Building Materials, in press.

3. Clifton, J.R., Carino, N.J., and Howdyshell, P., "In-Place

Nondestructive Evaluation Methods for Quality Assurance of

Building Materials," Technical Report M-305, Construction

Engineering Research Laboratory, Champaign, IL (March 1982),

81 pages.

4. Frobel , R.K., "Methods of Constructing and Evaluating

Geomembrane Seams," Vol . 2, Proceedings, International

Conference on Geomembranes, Industrial Fabrics Association

International, St. Paul, MN (June 1985), pp . 359-364.

5. Spanner, G.E., "Nondestructive Technique for Assessing Field

Seam Quality of Prefabricated Geomebr anes , " Vol. 2, Proceedings,

International Conference on Geomembranes, Industrial Fabrics

Association International, St. Paul, MN (June 1985),

pp. 369-374.

6. Manning, D.G. and Holt, F.B., "Detecting Delaminations in

Concrete Bridge Decks," Concrete International, Vol. 2,

No. 11 (1980) pp. 34-41.

7. "Ultrasonic Testing," Szilard J. , Ed., John Wiley & Sons,

New York (1982).

8. Dorn, B.E., Evans, H.E., and Torres, D.M., "Thermographic

Detection of Polymer /Metal Adhesion Failures," in "Adhesion

Aspects of Polymeric Coatings," Mittal, K.L., Ed., Plenum

Press, New York (1983), pp . 597-621.

9. McKnight, M.E. and Martin, J.W., "Quantitative Evaluation of

Blistering and Corrosion in Organic Coating Systems," in

"New Concepts for Coating Protection of Steel Structures,"

ASTM STP 841, Berger, D.M. and Wint, R.F., Eds., American

Society for Testing and Materials, Philadelphia, PA (1984),

pp. 13-20.

10. Reynolds, W.N. and Wells, G.M., "Video-Compatible Thermography,"

British Journal of NDT (January 1984), pp . 40-44.

22
11. Sayers, C.M., "Detectability of Defects by Thermal NonDestructive Testing," British Journal of NDT (January 1984),

pp. 28-33.

12. Dorn et al., op. cit., p. 616.

23
Table 1. Membrane Materials Included in the Study

No. Type Thi ckness

mm

(in.)

Comment

1 Black EPDM^ 1.5

(0.06)

Non -re i nf or ced ; smooth

surfaced

2 White EPDM^ 1.3

(0.05)

Non -rei nf orced ; smooth

surfaced

3 White CSME^ 1.0

(0.04)

Reinforced; surface is

not smooth but slightly

embossed

4 SBS -Mod if i ed

B i t umen

^ 4.6

(0.18)

Surfaced with white

granules; surface is not

smooth

1. EPDM indicates ethylene propylene diene terpolymer.

2. CSME indicates ch 1 or os u 1 f on ated polyethylene.

3. SBS indicates s tyr en e -bu t ad i ene -styrene

24
Table 2. Results of NDE Inspections of Large-Sized Membrane Specimens

Res u Its

Specimen Ultrasonic

Type Pulse Echo Infrared Thermography

Wheel Hot Air Blower^ Heat Lamps^

Coupl i ng

Seam

Alone

Voids detected

with wheel transducer using water as the coupling iiedluB.

• During heating, the voids were

only partially detected; the aln feature observed was perlaeter of the voids.

- During cooling, the voids were only partially detected; the

aln feature observed was perlneter of the voids.

- Wo air blown over cooling soeclwen ; ost voids were not detected; void

no. 6 produced an laage which

appeared square and not rectangular.

- Unheated air blown over cooling

speclwen : soBe voids were oartlallv

detected , priaarlly their perlaeter

shape; void nos. 1 fc 2 were not detected

Chamber

Spec i men

Voids detected

with wheel transducer using water as the coupling aedluB.

Host voids not detected during

heating; only void no. 2 was clearly visible; the outline of the perlaeter of void no. 4 was partially observed.

- Ho air blown over cooling speclaen;

voids not detected.

*

- Unheated air blown over cooling

speclaen : aost voids not detected;

only void no. 2 was clearly

visible; the outline of the perlaeter of void no. 4 was partially observed.

1. This was the method by which transient heat flow was induced in

the specimen.

25
Table 3. Results of NDE Inspections of Small-Sized Membrane Specimens

Membrane

Type

Results

Ultrasonic Pulse Echo

Direct Transducer

Contact

Infrared Thermography

Hot Air Blower

Black

EPDM

- Void detected.

- Void detection was sensitive to the pressure applied to the transducer

- Void was clearly visible while heating specimen

with hot air.

- After heating stopped, void Image faded In 15-20 s.

- Membrane was heated until underside was about

50 ®C (122 *F), then unheated air was blown over

the surface; void was visible; Image faded In about 15-20 s.

White

EPDM

• Voids detected.

- Void detection was sensitive

the pressure applied to the transducer

to

- Voids were clearly visible while heating

specimen with hot air.

- After heating stopped, void Images remained

visible for over 1 min.

- Membrane was heated until underside was about

50 *C (122 *F), then unheated air was blown over the surface; voids were visible; Images remained

visible for over 1 min.

Whi te

CSME

. Voids detected.

- Void detection appeared to be sensitive to pressure than In case of EPDM.

more

the

- Voids were clearly visible while heating

specimen with hot air.

- After heating stopped, void Images remained visible

for about 1 min.

- Membrane was heated until underside was about

50 *C (122 *F), then unheated air was blown over the surface; voids were visible but contrast was weak; Images remained visible for about 1 min.

SBS-Mod.

B i t umen

• Voids detected.

• Void detection was sensitive to the coupling nedlum; oil provided

detection; water was unsatisfactory.

- Voids were clearly visible while heating specimen

with hot air; Images were very sharp.

- After heating stopped, void Images remained visible

for over 3 min.

- Void detection appeared to be sensitive to pressure than In case of EPDM.

more

the

- Membrane was heated until underside was about

45 *C (113 *F), then unheated air was blown over the surface; voids were clearly visible; Images

remained visible for over 3 min.

26
1.2 m

(48

In.)

VOIDS

Description

Triangular void - 50 mm (2 in.) base,

68 mm (2.5 in.) height

Rectangular void - 50x25 mm (2x1 in.)

Rectangular void - 25x50 mm (1x2 In.)

Circular void - 50 mm (2 in.) in diameter

Circular void ~ 25 mm (1 in.) in diameter

Rectangular void

25x150 mm (2x6 in.)

Figure 1. Diagram of the 1.2 m (48 in.) Large-Sized Test

Specimen Indicating the Voids Incorporated in the Seam.

27
1.2 m (48 in.)

d

00

E

cv

:e'.

. •«..

;<o:

* * «»

• • ^

. 1 ^

*

. >

•e:

CO to.

• f

*.

E’ .«

(0.

—- •— 76 mm (3 In.)

A. TOP VIEW: Seams were equidistantly spaced across the specimen

1.2 m (48 in.) EDPM Membrane -V 1.5 mm (0.06 in.) ^

Fiberboard Insuiation —

13 mm (0.5 in.) Polystyrene Insulation^ y

50 mm (2 in.) ^

I

Seam

VflWiWii fiWiWiTii fifiWififlUillfnilATI

T

Wooden Deck

19 mm (0.75 in.) Gap between

insulation boards

B. SIDE VIEW: Seams were located above gaps between insulation boards

Figure 2. Plan of the Chamber Test Specimen.

28
A. Lap team with void - Rubber sheets totally separated at the void area

B. Lap seam with void - Rubber sheets in contact at the center portion of

the void

Figure 3. Types of Voids in Lap Seams.

29
NBS-114A (REV. a-BO) U.a. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See Instructions)

1. PUBLICATION OR

REPORT NO.

4. TITLE AND SUBTITLE

2. Performlns Organ. Report No. S. Publication Date

SEPTEMBER 1986

Investigation of the Use of Nondestructive Methods for Inspection of Seams of

Single-Ply Roofing Membranes

5. AUTHOR(S)

Walter J. Rosslter, Jr.

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8 . Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Naval Civil Engineering Laboratory

Port Hueneme, CA 93043-5003

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) Investigations were conducted regarding the use of the ultrasonic pulse echo and the

Infrared thermography nondestructive evaluation (NDE) methods for detecting voids

and delamlnatlons In adhesive-bonded seams of single-ply roofing membranes. Previous

studies had Indicated that these defects could be detected using the two NDE methods.

In the present study, voids Incorporated In 1.2 m (48 In.) long seam test specimens were located by the pulse-echo method using a wheel transducer to scan along the length

of the seam. These results Indicated that the ultrasonic pulse echo method using a wheel transducer can be useful as a field technique for assisting In the quality

assessment of seams.

When using the Infrared thermography method to evaluate the seam specimens, it was found that, unlike previous studies, only sections of some voids were detected and that

other voids were not detected at all. It was suggested that collapse of the voids due

to the applied pressure during seam formation might have provided insufficient surface

temperature differential between the bonded areas of the seam and the void areas of the seams during transient heat flow. The results raised concerns that the infrared

thermography method may not be practical for the general detection of voids of seams in

service.

12. KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

adhesive bonds; detection; infrared thermography; membranes; nondestructive

evaluation; roofing; seams; single-ply; ultrasonic pulse echo; voids

13. AVAILABILITY

Unl imited

I I For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

35

15. Price

UtCOW(M*OC