QUALITY AND CERTIFICATION
USE OF NATURAL VIBRATIONS IN FLAW DETECTION
OF HEAT-STRESSED EQUIPMENT
A. M. Konovalov,
V. I. Kugushev,
and A. Yu. Yakovlev
Translated from Novye Ogneupory, No. 12, pp. 57 – 60, December, 2016.
Original article submitted June 7, 2016.
A method of nondestructive testing of the elements of a construction to which there is no direct access is pre
sented. The method utilizes natural vibrations of the construction that have been excited by impacts of a spe
cial head of a hammer at specific spots. The method comprises a certain sequence that determines the position
of the points of application of the impacts and measurements of the vibrations, the distribution of the frequen
cies of the vibrations by range, and the construction of a limited number of ranges of the spectrum of frequen
cies of the natural vibrations. The state of a controlled element of the construction is determined from the dis-
tribution of the frequencies of the natural vibrations in the spectrum. Results of experimental investigations of
the inner jackets of eight nozzle heads by means of this method are presented.
Keywords: impact, natural vibrations, spectrum of frequencies, energy shortage, construction of ranges
Besides refractory materials, steel structures that require
cooling are used in a number of different heat-stressed ob-
jects. Among these structures we may note continuously
functioning combustion chambers and nozzle heads. Because
of their functional purpose, these structures must be sub
jected to periodic nondestructive testing. The elements of
such structures, which come into direct contact with
high-temperature flames, are enclosed in a cooling system
that prevents any possibility of direct access. Therefore, a
method that employs special natural vibrations of the con
struction as a whole may be used as a means of nondestruc
tive testing. On the one hand, it is possible to measure natural
vibrations on the outer surface of the object, while on the
other hand, the parameters of the natural vibrations depend
on the state of the object which is being tested.
We propose employing a method of nondestructive test
ing at time intervals when the unit which the nozzle head or
combustion chamber is a component of is not in operation.
Eight nozzle heads (Fig. 1) were subjected to nondestructive
Three of the eight heads possess defects of different
magnitude on the inner jacket. The inner jacket of the first
defective nozzle head has a large defect in the form of a
burn-through and multiple traces of burn-out of the metal on
the inner surface. The inner jacket of the second defective
Refractories and Industrial Ceramics Vol. 57, No. 6, March, 2017
1083-4877/17/05706-0665 © 2017 Springer Science+Business Media New York
AO TsKB MT Rubin, St. Petersburg, Russia.
Fig. 1. Nozzle head: 1) outer jacket of cooling system; 2) inner
jacket of cooling system, the state of which is the subject of nonde
structive testing; 3) flange through which the nozzle head is con
nected to the combustion chamber; Y) series of light impacts;
M) position of microphone.