This document discusses safety issues related to Yankee cylinders used in papermaking. It identifies several common reasons for Yankee cylinder failures, including increased steam pressure inside the cylinder, increased condensate levels, increased touch roll loading, and increased moisture in the incoming paper web. It then provides recommendations to address each of these issues, such as installing pressure switches and safety valves, regularly inspecting condensate removal pipes and seals, and monitoring systems to detect changes in process variables. Detection techniques for non-condensable gases are also outlined, as well as methods for monitoring vibrations or load fluctuations that can indicate increased condensate levels inside the Yankee cylinder.

1. A Discussion on
Yankee Safety Issues
By: D K Singhal

2. Disclaimer
This presentation is supplied as a self learning presentation, and is
subjected to the condition that the author accepts no liability
from the use of the same or from the techniques or information
provided within the same.
The information provided herewith is supplied exclusively for mild
steel fabricated yankee cylinders, and expected to be beneficial
to the users, however in case of any problem, may it be
operational, mechanical, breakdown or any other type, the
author cannot be held responsible for the same. Users are
welcome to consult the author in case any problem is observed.
It is strongly recommended to consult your machinery supplier,
yankee supplier, mechanical engineer, and process engineer
etc., before making any changes to the existing system.

3. Issues…
To protect yankee from unwanted
maintenance, e.g. grinding etc.
To ensure proper safety of two “M”s
Man and Machine.

4. Common Reasons for
failure…
Increased steam pressure inside
yankee.
Increased condensate level inside
yankee.
Increased touch roll loading.
Increased moisture with incoming paper
web.

5. Pressure inside yankee
Pressure is normally controlled using a
manual globe valve or alternatively with
a pneumatically controlled valve set at
desired setpoint.
Manual control has its own limitations,
while pneumatic control may allow more
steam to enter yankee cylinder in case
of a malfunction.

6. Increased Condensate
Level…
Increased condensate level can be due
to following reasons1. Siphon pipes leakage or broken.
2. Steam trap failure, strainer chocking
etc.
3. Rotary joint sealing or guide rings
broken.

7. Increased Condensate
Level…
In most of the cases, an increase in
condensate level remains unnoticed.
This results undesirable load due to
both increased weight of yankee as well
as increased pressure inside yankee to
compensate for reduced heat transfer
area due to condensate.

8. Increased Touch Roll Loading
Sometimes, in case of pneumatic or
hydraulic system failure (as the case
may be), the load on touch roll may
increase beyond permissible limits.

9. Increased Moisture
This is also possible that due to sudden
change in vacuum, or some other
process variables, the paper web
moisture content increases suddenly
resulting in undesirable stress on
yankee.

10. STEAM PRESSURE
CONTROL

11. Steam Pressure Control
It is strongly recommended to check all
upstream side valves, pressure gauges etc.
periodically to minimize the probability of
failure of the same. Pressure gauges must be
calibrated at regular intervals.
One mill reportedly uses two pressure
gauges, one for normal use and another
(normally valve shut off) for cross checking in
case the reading of the first is doubtful.

12. Steam Pressure Control
In addition, a pressure switch should be
installed at steam inlet line after final control
valve, but before rotary joint.
This switch should be connected to an alarm
to activate if the pressure increases beyond
limit. Any increase in steam pressure to MG
will therefore help the operators to do
corrective action.

13. Steam Pressure Control
A safety valve should also be installed
at the same line as above, set to bleed
off some amount of steam from yankee
in case steam pressure increases.
Since, this is very rarely to operate,
periodic checking and calibration of the
same MUST be done.

14. INCREASED CONDENSATE
LEVELS

15. Increased Condensate Level
In case siphon pipe or trey is broken or
cracked, it becomes impossible for the
condensate to reach to rotary joint. As a
result, condensate level increases.
These should be checked periodically,
at least once a year to ensure these are
properly welded/bolted.

16. Increased Condensate Level
In case of plugged strainers, or
malfunctioning of steam traps,
condensate cannot be removed from
yankee, and hence water level
increases. Such situation occurs in
case of air locking, steam locking,
mechanical failure of trap or scaling
deposition in steam trap and strainers.

17. Increased Condensate Level
Rotary joint carbon rings (seal rings and
guide rings) if broken, may allow a part of
steam from inlet side to escape from the
condensate side without entering yankee at
all.
Such a situation will result in increased
pressure at condensate line, and hence
condensate will not be removed from yankee.

18. INCREASED TOUCH ROLL
LOADING

19. Increased Touch Roll Loading
Malfunctioning of pressure regulating
valve in hydraulic or pneumatic system
may result in sudden increase in touch
roll loading.
In one study, it has been observed that
out of total forces acting on a yankee,
the touch roll loading accounts for
nearly 24% of load.

20. Increased Touch Roll Loading
Carefully designed hydraulic or pneumatic
systems with provision to control the pressure
beyond a certain value are a must.
It has been observed that presence of
moisture in pneumatic system results in
premature failure of regulators. Air should be
free from moisture.
In case of hydraulic system, periodical
cleaning of oil filter should be done to avoid
any oil contamination.

21. INCREASED MOISTURE IN
THE WEB

22. Increased Moisture
Sudden reduction in touch roll load,
vacuum or some other process variable
may result in increased moisture in
paper web. Due to increased moisture,
when a hot yankee comes in contact
with plenty of moisture, its surface
temperature reduces significantly. This
thermal shock can also affect yankee
adversely.

23. Increased Moisture
To avoid such situations, system must be
audited for its safeguards against failures.
In a typical case, it was noticed that the touch
roll load reduced to such a low value that it
lowered resulting in paper web break at
yankee section, and chocked uhle boxes.
Only a timely emergency stoppage could
protect felts from permanent damage.

24. Increased Moisture
For the case above, the mill installed a
pressure switch in pneumatic pipeline to
activate an alarm if the pneumatic
pressure reduced below minimum
desired pressure. Compressor failure,
severe leakage in pneumatic piping etc.
result in alarm so that the machine
operator can take a corrective or
preventive action as the case may be.

25. PROTECTION TECHNIQUES

26. Pressure Inside Yankee

27. PRESSURE INSIDE YANKEE
An inlet pipeline is given on the
following slide to illustrate how pressure
measurement and control can be
effectively done for a yankee.

28. Typical Yankee Inlet Piping
Schematic
PS
To
Yankee
SV
CV
Hooter
PS: Pressure Switch
PI: Pressure Gauge
SV: Safety Valve
CV: Control Valve
PI
CV
From
Steam
Header

29. Yankee Inlet Piping
It is very important to understand that the
pressure indicated by a pressure gauge -may
it be a bourdon tube type, or a pressure
transmitter with indicator or controller- is NOT
the pressure inside yankee as it is
considered. It IS the pressure at inlet of rotary
joint, and the pressure inside yankee would
be gauge pressure minus pressure drop
across rotary joint.

30. Yankee Inlet Piping
As the steam consumption, and hence steam flow
rate increases through yankee, this pressure drop
across rotary joint increases. That means, you
actually provide much lower pressure inside yankee
than the pressure gauge indicates.
Though seem unbelievable, this pressure drop may
be to the tune of half of the gauge reading in some of
the cases, i.e., if the gauge indicates an inlet
pressure of 3.2 Kg/cm2, fair chances are that the inlet
pressure id 1.8-2.0 Kg/cm2 only.

31. Measuring Actual Yankee Inlet
Pressure
Well, it is not practically possible, and
advisable too, to install a pressure gauge on
rotating yankee. But the same can be done
using a trick.
Condensate is removed form a cylinder at a
temperature corresponding to the saturation
temperature of steam at that pressure.
If a temperature gauge is installed just after
rotary joint, we can find out the steam
pressure inside yankee.

32. Measuring Actual Yankee
Pressure
The results obtained by this technique are
often surprising. In some cases, it has been
found that the hydraulic testing of yankee at
the fabricator site had been done at a
pressure 8 or 10 times more than that is
required for papermaking.
But, does that mean yankee is safe?

33. Yankee Pressure- Operational
Vs. Intermittent
In most of the cases, when the paper is
not running on machine, heat losses
through yankee shall are low, and
hence steam flow rate. That is why, the
pressure drop through rotary joint
reduces and pressure inside yankee
increase, even though the pressure
gauge indicates a reduction in the
same.

34. Yankee Pressure: A Typical
Case
In a particular case, a fabricated yankee was
analyzed as discussed above. The design
and operating data are as underDiameter:
4.2M
Shall Thickness:
62mm
Material:
A36 (ASTM)
Pressure at Inlet Piping:
3.3-3.7Kg/cm2

35. Yankee Pressure: A Typical
Case
That mill earlier considered that the
pressure inside yankee is to the tune of
3.3-3.7Kg/cm2. But, considering the
above, temperature measurement of
the condensate just after rotary joint
was done, and found that the
condensate temperature was to the
tune of 127-128°C. This corresponds to
2.0Kg/cm2.

36. Why to Install Safety Valve?
In case of paper running over yankee, it
extracts heat from yankee, as a result
of which, pressure reduces. But when
the paper is not there, e.g., in case of a
paper break, the pressure inside
yankee may increase and affect the
yankee adversely. To avoid the same, a
safety valve or pressure switch
connected to an alarm is
recommended.

37. Non-Condensable Gases
Non condensable gases are another major
source of pressure increase in yankee.
A minute quantity of non condensable gases
can easily reduce down heat transfer rates
significantly, due to which the operator is
bound to increase steam pressure to maintain
the desired production rates.

38. From Where NonCondensable Gases Appear?
In case where boiler feed water is hard, and
boiler water is also highly contaminated,
some de-scaling chemicals generate gases
like CO2 etc.
Also, if boiler feedwater temperature is very
low, presence of dissolved oxygen and air in
feedwater is released within boiler and these
gases travel alongwith the steam to enter
yankee. From the yankee, these cannot be
easily removed as steam trap does not
normally allow these gases to escape out.

39. Condensable Gases in the
System
Often it is very difficult to detect
presence of these gases within the
system, particularly if there is a scope of
increasing production rates.
On machines where the production is
limited by drying capacity, an increase
in pressure could be an indication for
the same.

40. Detection Techniques
For every grade of paper, and for every
speed and basis weight, note down the
normal operating pressure.
In absence of any other system, any
increase in pressure could be a
possible indication of presence of noncondensable gases in the system.

41. Detection Techniques
Here, the properties of steam can be used to detect
the presence of non-condensable in steam.
We know that Boiling point of water increases with
increase in pressure.
Hence, the temperature of condensate just after the
rotary joint increases with increase in pressure inside
yankee.
Due to presence of non-condensable gases, heat
transfer is reduces, which is compensated by
increasing steam pressure inside yankee.

42. Using Condensate
Temperature…
Thus, regular monitoring can reveal
presence of non-condensable gases in
yankee.
For example, if normally the
condensate temperature id to the tune
of 125-127°C, any increase beyond 5°C
can be considered possibly due to the
same.

43. Minimizing Non-Condensable
Gases
The first step is to minimize the
generation of these from the boiler
itself.
Desired number of blowdown, use of
suitable descaling and scale preventing
chemicals, timely descaling, maintaining
appropriate feedwater temperature
should be observed.

44. Minimizing Non-Condensable
Gases
In case non-condensable gases have entered
the system, another simple technique is to let
it blow away. This can be done by bypassing
steam trap in the condensate line. Though
this may lead to minor steam leakage, yet in
many cases, the effect is noticeable, and
condensate temperature decreases indicating
clearly that the heat transfer has improved
substantially.

45. INCREASED CONDENSATE
LEVEL

46. Increased Condensate Level
The problem with increased condensate
level is that in most of the cases, it go
unnoticed for a long time. It is quite
possible that machine is running
smooth without a break of paper for a
long time, and sudden effect of
condensate level increase is noticed.

47. Increased Condensate Level
In a typical case, vibrations started to
appear in yankee framings, and it was
decided to shut the machine and check
yankee internally. Boiler steam supply
was discontinued, and it was decided to
run the paper without steam as long as
possible to get yankee cooled down
early.

48. Increased Condensate Level
Under that situation, machine could be run for
nearly 30-40 minutes without steam.
On checking, it was found that the yankee
was ¾ full (height wise).
One can understand how dangerous it can be
to operate a yankee under such
circumstances, but without knowing the
condensate level in yankee what can be
done?

49. Condensate Removal per
Rotation of Yankee
It is easy to estimate condensate
removed from yankee per revolution.
Divide machine speed with yankee
circumference to achieve yankee RPM.
Now divide condensate removal (or
steam consumption) per hour and
divide the same with 60 (to convert
hours to minutes) and then with yankee
RPM.

50. Condensate Removal per
Rotation of Yankee
For a typical case, steam consumption was
3000 kg/Hr. Machine speed was 210mpm
and yankee circumference was 13.3M.
So the condensate removal per yankee
rotation would be calculated asYankee RPM = 210/13.3 =15.79 rpm
Condensate = 3000/(60*15.79) = 3.16 kg per
revolution.

51. Condensate Removal per
Rotation of Yankee
As one can see that this is a very small
quantity. Also, considering two treys in
a yankee, the water to be lifted per trey
operation is less than two liters.

52. Effect of Condensate Level
Increase
While condensate level is increased,
the trey do lift condensate to transfer
the same to siphon pipe, from where it
cannot move forward, and fells back
into yankee. But due to the size of
treys, these bear a resistance to move,
which can be observed by fluctuating
drive load. The more is the trey size, the
more would be load fluctuation.

53. Effect of Condensate Level
Increase
With increase in condensate level,
some vibrations do start in the yankee
framings. In case the mill has installed
vibration analyzers, any increase in
condensate level can be easily noticed.
For the mills which do not have installed
vibration analyzers in yankee framings,
or do not intend to do so due to high
cost, here is a simple solution.

54. Indicating Vibrations in
Yankee Framings
If any member such as angle or
channel is mounted with yankee
framings in such a way that it is
supported at one end, and the other
end is free, it will oscillate due to
vibrations. A regular observation to its
other end if vibrating severely will
indicate the possibility of some problem
such as condensate filling inside
yankee.

55. Indicating Vibrations in
Yankee Framings
Yankee
Frame
Yankee
Frame
Vibrating
Member

56. Using Ampere Meters….
In some cases, the yankee framings may be
so rigid that there are no significant vibrations
observed in case condensate gets filled up in
yankee. An alternate to the technique shown
above is to put an analogue ampere meter for
yankee drive load. A fluctuation in load,
particularly twice in every rotation of yankee
(For two treys) is a clear indication for the
same.

57. Using Ampere Meters….
In case the dimension of treys is relatively
small, these will not create any resistance to
condensate and hence amperage fluctuation
as indicated above would be very small. As
the trey has to handle only a very small
amount of condensate every time, there is no
need to increase trey size. So another
technique is proposed here to get informed in
case of condensate level increase.

58. A Design Modification
The treys are normally designed in such a
way that the condensate collected by these is
immediately transferred to siphon pipes, from
where it can be removed through rotary joint.
In case some of the condensate does not
move to siphon pipe, it falls back inside
yankee shall, but it does apply some extra
load on drive system.A similar design with
increased area will create more resistance to
drive.

59. Normal Trey System
Yankee
Trey

60. Proposed Baffles
Proposed
Baffle

61. Proposed Baffles
As indicated in the drawing in the previous
slide, the dimensions of the same are
designed considering the steam
consumption, yankee dimensions, trey
dimensions, drive system (whether sectional
or line shaft) etc. This baffles are not welded
to shall hence one can be assured that there
would be no surface deformation. Yet, as a
matter of precaution, baffles must be welded
before yankee grinding.

62. Before Installation
Before installation of baffle, one must ensure that the
yankee is balanced.For the same, all other driven
elements, e.g. wire part, press part, pope reel etc. are
stopped in case of a line shaft drive. Yankee is
rotated at very slow speed with all doctor blades
unloaded, and touch roll lowered.
Any unbalance will result in fluctuation of load
(amperage) once for every revolution of yankee
multiplied by number of baffles.
Baffle should be installed only after balancing.

63. Baffle Commissioning
After installation of baffle, first of all, balancing of
yankee has to be checked. Having done that, the
baffles should be checked for suitability. For the
same, water is filled inside yankee, and condensate
line is flanged dummy. This way, no condensate
(water) can be removed from yankee. Now yankee is
rotated at different speeds, and fluctuation in load
(difference between maximum and minimum
amperes) is noted.This load fluctuation will be more
at higher speeds than that at lower speeds.

64. Baffle Commissioning
From the noted amperage fluctuation values,
it must be ensured that the drive should not
trip at maximum load condition.
Also, baffles should be mechanically strong
enough to withstand shock load that may
arise during operation in case of flooding
yankee.
It should also be checked that the baffles do
not obstruct condensate flow in case of
normal operation of yankee.

65. Conclusion
The basic approach to be followed is to
detect, measure and correct for any
action that has to be done for the safety
of any equipment.
Above all, a team work and association
of every individual towards the goal of
COMPLETE SAFETY is a must.

66. A Final Word….
Let us-
HOPE FOR THE BEST
&
PREPARE FOR THE
WORST.

67. Feedback
Please send your feedback to:
D K Singhal
Deveshksinghal@rediffmail.com
Deveshksinghal@gmail.com

68. D K Singhal
Basically an M.E. (Pulp & Paper) from Institute of Paper Technology, (University
of Roorkee, now IIT, Roorkee), Saharanpur, 1993. Did B.E. (Pulp & Paper) from
the same institute in 1990. Certified Energy Auditor from Bureau of Energy
Efficiency (BEE), India.
Having about 15 years of experience and author of more than three dozen
technical & research papers covering a vide range of topics including waste
paper sorting, pulping, waste paper recycling, energy conservation, optimization,
chemical recovery, paper mill electricals, power generation, rewinder
optimization for trim loss minimization, paper making, process instrumentation &
automation, computer simulation, quality monitoring etc.
Contact:
D K Singhal, Sargam Theatre,
Chandpur 247 625, Dist. Bijnor
Phone: 01345:220140,222330 (O)
Fax: 01345:224140 Mobile: 09412713426
E-mail: deveshksinghal@rediffmail.com chandpurpapers@yahoo.com