1. Boiler Tubes

2. Economizer Tubes
Steam Drum (Wrapper Sheet)
Air in
Tube Sheet
Waterwall Tube
Generating Tubes
Downcomer
Water Drum
Superheater Tubes
Screen Tubes
Waterwall Header

3. Classification of Tubes
Generating Tubes
Screen Tubes
Downcomers
Superheater Tubes
Water Wall Tubes (Roof Tubes and Floor Tubes)
Support Tubes
Risers
Circulating Tubes

5. Boiler Tubes Tubes Required for One Boiler Tube Type Number O.D.
Wall Thickness
Screen tubes – Two Rows
30 each
2.0”
0.165”
Generating Tubes – 19 Rows
60 each
1.25”
0.120”
Refactory Retainer Waterwall Tubes 28
Rear Waterwall Tubes 45
Side Waterwall Feeders 19
Rear Waterwall Feeders
Rear Waterwall Risers 29

6. Tubes Required for One Boiler
Boiler Tubes
Tubes Required for One Boiler
Tube Type
Number
O.D.
Wall Thickness
Downcomers 8
4.0”
0.203”
Superheater Support 2
3.0”
Superheater – 1st Pass 54
1.25”
0.120”
Superheater – 2nd Pass 51
Superheater – 3rd Pass
Superheater – 4th Pass 45
Superheater – 5th Pass 42
Economizer Elements 72
2.0”
0.165”

7. Generating Tubes
Generating tubes make up the main tube bank of the boiler. They generate steam from the water within. These tubes are generally small in diameter in order that the boiler will have a high evaporation rate and a fast response.

8. Screen Tubes
Screen tubes are large diameter water tubes placed between the fires and the main generating tube bank, or between the fires and the superheater tubes. They protect these smaller tubes from the intense radiant heat.
Usually consist of 2 to 4 rows of tubes

9. Downcomers
Downcomers supply the lower water drums and waterwall headers with water from the steam and water drum.
Downcomers are the largest diameter tubes in the boiler.
Downcomer are located away from the boiler heat source, possibly behind the generating tubes, between the inner and outer boiler casing or outside the boiler.

10. Downcomers The design capacity of the downcomers depends on:
The total capacity on the generating tubes in weight of water evaporated per hour
The desired circulation characteristics of the boiler

11. Water Wall Tubes
Water wall tubes are tubes installed along the walls, floor and roof of the furnace and either freely exposed, partially covered, or completely embedded in the refractory of the boiler.
Water is supplied to the water wall tubes from the steam and water drum by downcomers and headers.

12. Water Wall Tubes
Steam generated in the water wall tubes is returned to the steam and water drum by means of water wall headers and risers or may be returned to the rear header in the straight tube boiler.

13. Water Wall Tubes Advantages of Water Wall Tubes are:
Water wall tubes protect the refractory of the boiler
The absorption of large amounts of heat from the furnace which permits higher combustion rates
They increase the steam generating capacity of the boiler

14. Water Wall Tubes
The reduction of maintenance of the refractory by maintaining lower brickwork temperature.
The equalization of furnace temperature

15. Water Wall Tubes Types of water wall tubes
Bare tubes fully exposed in the furnace
Partially studded and partially covered with refractory (Plastic Chrome Ore)
Fully studded and completely covered with refractory.

16. Water Wall Tubes
The reason for the studding is to serve as an anchor for the refractory and to absorb heat from the refractory and transfer it by conduction in the tubes

17. Support Tubes
Support tubes are large diameter, thick walled water tubes used in vertical tube boilers for support of the upper steam and water drum.
The support tubes may have hangers attached along their length for the purpose of giving support to the superheater tubes

18. Risers
Risers are large diameter tubes that return the steam and water mixture from the waterwalls back to the steam and water drum.
A closed circuit comprising the steam and water drum, the downcomers, the water wall tubes, water wall headers and risers is thus formed

19. Circulating Tubes
Circulating tubes are large diameter found in straight sectional header boilers connecting the rear sectional headers with the steam and water drum.
Their purpose is to return steam and water mixture that collects in the rear headers back to the steam and water drum

20. Boiler Tubes
What is the difference between a tube and pipe?

21. Boiler Tubes Boiler tubes are designated by their outside diameter
Wall thickness is determined by boiler pressure they will be subjected to
Boiler tube size will determine how quickly boiler can respond to change of load demands (surface area vs. volume)

22. Boiler Tubes
Boiler tubes are secured to the tube sheets by rolling or welding
Leaking tubes are plugged or replaced

23. Boiler Tubes
The wall thickness is usually designated by BWG – Birmingham Wire Gauge.
Tube are made out of seamless steel or seamless high temperature steel alloys depending on the location in the boiler.

24. Boiler Tubes
Boiler tube size will determine how quickly boiler can respond to change of load demands (surface area vs. volume)
The tubes are long enough to allow the tube to extend a minimum of ¼” and not more than ½” beyond the end of the tube sheet.
Pipe (1/8” to 12”) is designated by its nominal diameter.

25. Boiler Tube Size
The size of the tubes have a large bearing on the operating characteristics of the boiler.
As the size of the tube used in construction of the boiler is reduced the ratio of heating surface are per unit volume of water becomes larger.
Since more small sized tubes can be placed in the same space, more heating surface is obtained

26. Boiler Tube Size
Greater heating surface areas per unit volume of water and more tubes result in higher evaporation rates.
High evaporation rates result in a boiler with a fast response to changes in load.

27. Boiler Tube Size
Calculate the surface area and volume of Boiler tube which is 4 inches in diameter and 1 inch long.

28. Boiler Tube Size Surface area equals tube circumference X tube length.
Area = ΠD*L
Area = 3.14*4*1
Area = in2

29. Boiler Tube Size Volume equals cross section area times length.
Volume = (Π/4)*D2*L
Volume = * (4*4) * 1
Volume = in3

30. Boiler Tube Size Ratio of surface area to volume contained
Surface Area/Volume
Surface Area/Volume = /
Surface Area/Volume = 1 to 1 ratio

31. Boiler Tube Size
Calculate the surface area and volume of Boiler tube which is 2 inches in diameter and 1 inch long.

32. Boiler Tube Size Surface area equals tube circumference X tube length.
Area = ΠD*L
Area = 3.14*2*1
Area = in2

33. Boiler Tube Size Volume equals cross section area times length.
Volume = (Π/4)*D2*L
Volume = * (2*2) * 1
Volume = in3

34. Boiler Tube Size Ratio of surface area to volume contained
Surface Area/Volume
Surface Area/Volume = /3.1416
Surface Area/Volume = 2 to 1 ratio

35. Boiler Tube Size
The 2” tube has twice the surface area to volume then the 4” tube.
So the 2” tube will have a evaporation rate twice that of the 4” tube.

36. Boiler Tube Size
Calculate the velocity of the water thru the same 2” and 4 inch tubes for a 600 psia boiler.
ṁ = ρVA
ṁ = Mass Flow (lbs/hr)
ρ = Density (lbs/ft3)
V = Velocity (ft/sec)
A = Area (ft2)

37. Boiler Tube Size ṁ = ρVA ṁ = VA/νspec νspec = Specific Volume
ṁ = 60,000 lbs/hr
From Steam Tables νf =

38. Boiler Tube Size
νf = ft3/lbm
Area of the 2” tube is

39. Boiler Tube Size νf = 0.02013 ft3/lbm Area of the 2” tube is A = ΠD2/4
A = ft2

40. Boiler Tube Size ṁ = VA/νf
60,000 lbs/hr = V * ft2 / ft3/lbm

41. Boiler Tube Size
Velocity = ft/sec

42. Boiler Tube Size
Calculate the velocity of the water thru the 4 inch tube for a 600 psia boiler.
ṁ = ρVA
A = ΠD2/4
A = 3.14*((4/12)2)/4
A = ft2

43. Boiler Tube Size ṁ = VA/νf
60,000 lbs/hr = V * ft2 / ft3/lbm

44. Boiler Tube Size
Velocity = 3.85 ft/sec

45. Boiler Tubes
Boiler Tubes are secured to the drums or headers by rolling or welding.

46. Boiler Tubes
The drum or header which the tube is going to rolled must be clean a free of any chemicals, dirt or any other solids.
The holes must clean and be as perfectly circular as possible.
The ends of the tubes should extend beyond the drum or header by ¼ to 3/8 inches.

47. Boiler Tubes
The tubes are usually held in place by collars on either end of the tubes on the outside of the drums or headers

48. Boiler Tubes
Once the tube is securely held in place and expanding or rolling tool is place inside the tube and expands diameter of tube against the metal of the drum or header.
When the tube is expanded and is secured the portion of the tube which is extending out in the drum or header is them flared or “belled” with a belling tube.

49. Boiler Tubes
This aids in reducing fluid friction as water enters or leaves the tubes.
When all the tubes have been rolled the boiler is closed and filled with water.
The water pressure is pumped up to 1.5 times the design pressure (Mean Allowable Working Pressure – MAWP).
If any tubes leak the are then rerolled and retested.

50. Boiler Tubes

51. Boiler Tubes

52. Boiler Tubes

53. Boiler Tubes
Tubes the are secured in the boiler by welding must be done by a certified welder with a certified welding procedure which must be approved by the U.S.C.G. and the American Bureau of Shipping (ABS).
After all the tubes have been welded in place the boiler will require a 1.5 times MAWP hydro test.

54. Boiler Tubes
The Coast Guard or ABS my require that some or all the welds be X-Rayed.
If there are any leaks, the weld will have to be ground out and then rewelded.
The boiler will have to be retested.
If you have to do any welding repairs on the boiler, you are required to notify the Coast Guard at your first port of call.

55. Leaking Boiler Tubes
If it is determined that you have a leaking boiler tube and the boiler tube can not be replaced. The boiler tube will have to plugged.
You will have to determine which tube is leaking.
This is usually done by filling the boiler with water and pressurizing it.

56. Leaking Boiler Tubes
Once you have determined which boiler tube is leaking you have to gain access to it on the waterside of the boiler.
The tube is then plugged at both ends with metal plugs that are part of the spare parts for the boiler.
You must ensure that the tube you are plugging has a hole in it.

57. Leaking Boiler Tubes
If you do not hole the tube its is possible that the air in the tube will expand while the boiler is being brought up to pressure and blow out the plugs.

58. Leaking Boiler Tubes