Tissue360 - Fall/Winter 2017 - 40
Yankee Dryer Shell Thickness
For the most accurate result, a cold measurement of the dryer
using measurement tape is recommended
This article discusses yankee dryer shell thickness measurement techniques and reviews the types of measurement differences
(variances) that may occur depending upon the measurement method,
the shell conditions (temperature and pressure), and the shell materials
(gray cast iron and welded steel).
Information and calculations are provided to help quantify measurement differences (variances) at different shell conditions that help to
provide guidance on adjustment of these measurements for review of
different shell thickness reports in yankee dryer files.
are shared that show how shell measurement differences (variances) can
be explained or accounted for so that the most accurate shell thickness
can be recorded and reported. Recommendations for measurement
techniques will help in improving the understanding of how yankee
dryer shell thickness can be measured and how that shell measurement
can be used to permit safe operation of the yankee dryer pressure vessel
and protect papermaking personnel and the general public.
* The most accurate shell thickness determination is obtained by using
a circumference measuring tape (or diameter measuring tape) of the
yankee dryer when it is in a "cold" condition (yankee dryer at room
temperature and no internal pressure).
* Ultrasonic thickness measurement should never be used to record
gray cast iron shell thickness due to the large variation in sound velocity of cast iron within the same casting. Data indicate a minimum-tomaximum sound velocity spread of about 6 percent in high-strength
gray cast iron.
The purpose of this article is to share information on yankee dryer
shell design thickness and ways that it can be measured. Basic equations
WHAT IS THE THICKNESS OF A YANKEE DRYER SHELL?
There are two types of yankee dryer shells - plain (smooth) bore and
grooved (ribbed) bore.
Many years ago, all yankee dryers had plain (smooth) bores. In the
1950s and 1960s, the first dryers had their shell inner surface grooved
so that heat transfer through-the-shell (drying rate) could be improved.
Today, almost all yankee dryers are of the grooved (ribbed) bore design.
In yankee dryers with a plain (smooth) bore, the total thickness is the
actual shell thickness. There is no adjustment necessary to the thickness
when calculating the maximum allowable working pressure (MAWP),
the pressure-retaining capability of the vessel.
In yankee dryers with a grooved (ribbed) bore, the effective thickness
of the shell needs to be calculated (adjusted) and then used to calculate
the MAWP of the grooved yankee dryer.
Fig.1: Plain (Smooth) Bore
Fig. 2: Grooved (Ribbed) Bore
Grooved (Ribbed) Bore
Plain (Smooth) Bore
Fig. 3: Calculating the Area if Solid
Tissue360º FALL/WINTER 2017
Fig. 4: Calculating the Groove Area