Condition monitoring approaches applied to a
polychloroprene cable jacketing material
Kenneth T. Gillen
)
, Roger A. Assink, Robert Bernstein
Sandia National Laboratories, Materials Aging & Reliability, PO Box 5800, Albuquerque, NM 87185-1411, United States
Received 3 November 2003; accepted 3 January 2004
Abstract
In this paper we examine the utility of several promising material condition monitoring (CM) techniques applied to a commercial
polychloroprene cable jacketing material used in nuclear power plant applications. These include two relatively unknown
approaches, cross-sectional modulus profiling and NMR T
2
relaxation time measurements of solvent-swelled samples, as well as
three more commonly used approaches, density, gel fraction and solvent uptake. The results from each approach were compared to
tensile elongation measurements, the usual standard approach for monitoring degradation of elastomers. Degradation was carried
out at three temperatures and at four combined radiation plus thermal environments, all of which were selected (by theoretical
modeling and later confirmed by cross-sectional degradation mapping) such that oxidation proceeded uniformly throughout the
cross-section of the material. This allowed macroscopic condition monitoring measurements to be made in the absence of
anomalous diffusion-limited oxidation effects. Of the techniques examined, modulus profiling, solvent uptake and NMR T
2
measurements correlated extremely well with the elongation measurements and therefore showed substantial potential as CM
approaches for this material. This is not unexpected since all of these techniques are sensitive to crosslinking of the material and the
deterioration of the elongation is itself dominated by material hardening and thus by crosslinking.
Published by Elsevier Ltd.
Keywords: Aging; Polychloroprene; Condition monitoring; Modulus; NMR relaxation; Solvent uptake; Swelling
1. Introduction
For many years there has been intensive interest
focused on various approaches that could allow nuclear
power plants to safely operate beyond their 40-year
original license period. Among the most important
safety-related issues is the continued viability of safety-
related electrical cables [1e7]. During normal operation,
many of these cables are exposed to fairly high temper-
ature aging environments and some are also exposed to
reasonably high radiation environments. If an accident
such as a loss of coolant accident (LOCA) occurred, the
ambiently aged cable must have sufficient mechanical
properties remaining after normal aging such that it will
remain viable during the accident. Since replacing cable
in a nuclear plant can be a complex and very expensive
operation, periodic determination of the condition of
cables is of considerable interest. The most commonly
utilized traditional method for determining condition of
low voltage electrical cable materials involves measuring
the ultimate tensile elongation of the material of interest.
When the elongation drops sufficiently, it is assumed
that the cable may not remain viable if an accident
occurred. The amount of drop to ‘‘failure’’ is somewhat
arbitrary but a consensus seems to be developing that
50% absolute elongation represents a conservative fail-
ure criterion [6].
Unfortunately elongation measurements are consid-
ered to be destructive since they require that fairly large
samples be removed from a cable for testing. Since this
can create problems for nuclear plants when samples
from a large number of areas in the plant need to be
periodically tested, there has been considerable effort
)
Corresponding author. Tel.: C1-505-844-7494; fax: C1-505-844-
9781.
E-mail address: ktgille@sandia.gov (K.T. Gillen).
0141-3910/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.polymdegradstab.2004.01.018
Polymer Degradation and Stability 84 (2004) 419e431
www.elsevier.com/locate/polydegstab