boiler superheater

1. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Date : 29 November 2006
Presentation for:
Paiton: Superheater Failure
• Problem area
• Facts
• Direct cause of pipe bursting
• Root cause
•Explanation root cause
• Conclusion
• Solution
• Discussion.

2. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Problem Area:
• Final super heater suffers from pipe
bursting during start up.

3. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Facts
• Super heater tube condition is in general
good.
• No excessive erosion or corrosion is found
• Lose scaling is found in final super heater
• Pipe bursting is caused by short term
overheating. (Report Matcor Pte Ltd)
• All pipe bursts happened directly after start
up

4. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Cause of Pipe Bursting
• The direct cause of pipe bursting is due to
scaling blockage of the superheater tubes
• The blockage causes insufficient flow in the
superheater.
• Insufficient flow results into insufficient cooling.
• Material temperatures will rise above design
temperature and weakens the pipe.
• Pipe burst.

5. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Root Cause
• The root cause of the
actual failure is the
scaling build up in the
tubes. This scaling
brakes of once it is
getting to thick. This
due to thermo shock.
(start up)
• This process is also
called exfoliation.

6. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Scaling Build up
• Scaling build up takes place due to a
thermal oxidation process.
• This thermal oxidation process goes faster
on higher metal temperatures.
• Oxidation process is different for several
types of metals.

7. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Typical Oxidation Temperatures
• Temperatures at which thermal oxidation becomes excessive
• Operating temperature superheater:
• Inlet 460C
• Outlet 530C
SA209 Gr T1 Carbon Alloy Carbon 550 C
SA213 - T12 1Cr - 0.5Mo 570 C
SA213 - T22 2.25Cr - 1Mo 600 C
SA213 - T91 9Cr - 1Mo 770 C
SA213 - TP304H 18Cr - 8Ni 870 C
SA213 - TP347H 18Cr - 10Ni 900 C

8. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Materials Used in Superheater
Inlet 457C
Outlet 531
A = OD 57.15 TH 6.09 18%Cr 10% Ni SA 213 TP-347H C.D.
B = OD 57.15 TH 10.66 18%Cr 10% Ni SA 213 TP-347H C.D.
C = OD 57.15 TH 12.06 2.25% Cr 1% MO SA 213 T22 HF
D = OD 53.97 TH 7.16 9%Cr 1% MO SA 213 T91 HF
E = OD 53.97 TH 8.89 18%Cr 8% NI SA 213 TP-304H C.D.
F = OD 53.97 TH 10.8 2,25% CR 1% MO SA 213 T22 HF
G = OD 53.97 TH 7.16 1% CR 0.5% MO SA 213 T12 HF
H = OD 63.50 TH 12.87 2,25% CR 1% MO SA 213 T22 HF
I = OD 53.97 TH 11.43 2,25% CR 1% MO SA 213 T22 HF
J = OD 53.97 TH 12.06 2,25% CR 1% MO SA 213 T22 HF
K = OD 50.80 TH 12.87 2,25% CR 1% MO SA 213 T22 HF
L = OD 53.97 TH 12.97 2,25% CR 1% MO SA 213 T22 HF
M = OD 63.50 TH 6.60 18%Cr 8% NI SA 213 TP-304H C.D.
N = OD 69.85 TH 13.58 2,25% CR 1% MO SA 213 T22 HF
P = OD 63.50 TH 8.89 18%Cr 10% Ni SA 213 TP-347H C.D.
R = OD 63.50 TH 7.16 Carbon Alloy P-3 SA 209 GR. T1 HF
S = OD 53.97 TH 6.09 Carbon Alloy P-3 SA 209 GR. T1 HF
T = OD 63.50 TH 7.16 18%Cr 8% NI SA 213 TP-304H C.D.
V = OD 69.85 TH 13.58 18%Cr 10% Ni SA 213 TP-347H C.D.
W = OD 50.80 TH 6.60 18%Cr 8% NI SA 213 TP-304H C.D.
SA209 Gr T1 Carbon Alloy Carbon 550 C
SA213 - T12 1Cr - 0.5Mo 570 C
SA213 - T22 2.25Cr - 1Mo 600 C
SA213 - T91 9Cr - 1Mo 770 C
SA213 - TP304H 18Cr - 8Ni 870 C
SA213 - TP347H 18Cr - 10Ni 900 C

9. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Possible Problem Areas
Inlet 457C
Outlet 531
SA-213 T22 Material
Subjected to longterm and short term
overheating and scale formation
In general SA-213 T12/T22 Material
Subjected to scale formation.
Overheating unlikely, unless tube
complete blocked.

10. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Understanding about Metal
Temperature
• The metal temperature is the temperature of the
metal and not the steam temperature.
• Steam temperature is lower than metal
temperature.
• Measurement in the penthouse are steam
temperatures
• The tube part in the penthouse is heated up by
the steam.

11. Galen Technologies & Services Pte. Ltd.
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Factors that Dictates Metal
Temperature
• Convection heat
• Radiation heat
• Steam flow
• Steam velocity
• Internal scaling
• External fouling

12. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Convection Heat
• A general rule for superheaters is that the
gas FILM around a tube is roughly 550C
lower than the flue gas temperature.
• In this case it means that the metal of the
superheater tube is in direct contact with a
gas temperature of 1250 – 550 =700C

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Radiation Heat
• Radiation heat is dictated by the flame
color.
• The final superheater in this configuration
“sees” the direct flame. This has an impact
on the metal temperature.
• Metal temperature will increase.

14. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Superheater Flow
• The amount of steam going through the
superheater is directly related to the
cooling of the metal.
• Normal minimum flow figures for a
superheater that “sees” the fire in an oil or
coal fired boiler are 25% to 30% of full
load.
• In his configuration a save minimum load
would be 600 t/h.

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Boiler specialists
Steam Velocity
• The steam velocity is directly related to the
heat transfer from tube to steam.
• Normal steam velocity figures during full
load are around 40 m/sec.
• In this configuration steam velocity at full
load is app 40 m/sec.
• On minimum load 10% during silica
purging 4 m/sec.

16. Galen Technologies & Services Pte. Ltd.
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Velocity Calculation
Maximum steamflow is 2300t/h. This steam goes through 580 tubes.
Average flow per tube = 2300/580 = 4t/h. Temp average 500C
Pressure 160 Bar
Minimum steamflow is 10% of 2300t/h during silica purging.
This steam goes through 580 tubes.
Average flow per tube = 230/580 = 0.4t/h. Temp average 500C
Pressure 160 Bar

17. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Steam Velocity at Full Load
Calculation

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Un-balance

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Scaling Thickness
• Scaling in superheater tubes should not
exceed 200Micron thickness.
• Above this thickness heat transfer will
decay. This will result in higher metal
temperatures.
• Faster thermo oxidation process.
• Scaling is easily formed in Carbon steel
T11, T12, T22 and at higher temperatures
in T91

20. Galen Technologies & Services Pte. Ltd.
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Scaling Thickness versus
Material Temperature
Tube wall
530
570
530
610
1200
1200
Scaling thickness

21. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Conclusion
• Relatively thick scaling is formed during the 8 years of
operation of the boiler.
• The scaling comes off and blocks the superheater tubes
with overheating and tube rupture as result.
• The forming of this type of scaling in relatively hot zones
is nothing abnormal. In the Netherlands it is common to
do chemical cleaning after 6 to 10 years of operation to
remove the formed scaling.
• Further due to very low steamflows during silica purging
unbalance over the superheater tubes can very easy
occur with overheating as a result.

22. Galen Technologies & Services Pte. Ltd.
Boiler specialists
Solution and Preventive
Maintenance
• Remove scaling by chemical cleaning.
– Can be done with HF (Extremely dangerous and therefore complicated)
– Can be done with FAX (phosphate solution relatively harmless for
environment.)
• Removal of scaling by running a high load over the bypass
might work for short term. Calculation show there is not
sufficient mass flow for a secure result.
• Increase steam flow during silica purging to at least 600 t/h
• Avoid low steam flows during turbine start.
• Check the T22 material superheater tubes at the outlet for
long term overheating. Take replica’s.

23. Galen Technologies & Services Pte. Ltd.
Boiler specialists
DISCUSSION