Maxims and Instructions for the Boiler Room

Chapter V: Introduction (4)

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The stays should be well fitted, and each one carefully tightened, and, as far as possible each stay in a group _should have the same regular strain upon it_—if the “pull” all should come on one the whole are liable to give way.

DIMENSIONS AND SHAPE OF ANGLE AND T IRON.

The condition of a boiler can be learned by tapping on the sheets, rivets, seams, etc., to ascertain whether there are any broken stays, laminated places, broken rivets, etc.

Fig. A represents the method of preparing testing pieces of boiler plate, for the machines prepared specially to measure their elongation before breaking, and also the number of pounds they will bear stretching before giving way. Fig. B exhibits the same with reference to the brace and other =O= iron.

RULES AND TABLES

FOR DETERMINING AREAS AND CALCULATING THE CONTENTS OF STEAM AND WATER SPACES IN THE STEAM BOILER.

In order to ascertain the number of braces, which are necessary to strengthen that part of the boiler head, which is not stayed by the tubes, it is first necessary to know its area; the part to be stayed is _a segment of a circle_.

_The length of the segment_ is measured above the top row of the tubes, and its _height or width_ is equal to the distance from the top of the tubes to the top of the boiler shell.

Since, however, part of this segment is braced by the boiler shell, and also by the top row of the tubes, it has been generally agreed that the length of the segment should be measured two inches above the tubes, and the height or width, should be measured from a line, drawn two inches above the tubes, to a point within three inches from the top of the boiler shell, as shown in the illustration by the dotted line. Thus, referring to Fig. D, the length of the segment is equal to l, and the height is equal to h.

RULE. The area of a segment may be obtained, very approximately, by _dividing the cube of the width (or height) by twice the length of the chord, and adding to the quotient the product of the width into two-thirds of the chord_.

EXAMPLE. If we suppose the height h of the segment in Fig. D to be equal to 18 inches, and the length l to be equal to 48 inches, we have

18³ ÷ (48 × 2) + (48 × 2/3 × 18) = 60.7 + 576.0 = 636.7 square inches.

In order to calculate the contents of the steam and water spaces of a boiler, the same rule, as above, may be employed. The volume of the steam space may be readily obtained by the above rule, _taking the distance from the water level to the top of the shell for the height, and the diameter of the shell, measured at the water line, for the length of the segment lines_.

The area of the segment thus found, expressed in square inches, divided by 144, and multiplied by the length of the boiler in feet, is equal to _the steam space, in cubic feet_, this result is slightly reduced by the space occupied by the braces.

In order to find the volume of the water space, it is first necessary to _find the total area of the boiler head_, and this _minus the area of the segment above the water line_, is equal to the area of the segment below the water line. From this must also be subtracted _the combined cross sectional area of the tubes_.

Thus, the rule for finding the volume of the steam space in cubic feet.

1. _Find the area of the segment of the boiler head, above the water line, in square inches._

2. _Divide this by 144, and multiply the quotient by the length of the boiler in feet._

To find the volume of the waterspace in cubic feet.

1. _Find the area of the boiler head in square inches._

2. _Multiply the square of the outside diameter of one tube by .7854, and multiply this by the number of tubes, and add to the product, the area of the segment above the waterline_.

3. _Subtract 2 from 1, and divide the remainder by 144._

4. _Multiply the quotient by the length of the boiler in feet._

To find the number of braces, necessary for the flat surface above the tubes.

1. _Find the area of the segment of the boiler head, which is to be braced, in square inches._

2. _Multiply the area, thus found, by the steam pressure in pounds per square inch._

3. _Multiply the cross sectional area of one brace by the number of pounds, which it is allowed to carry, per square inch of section._

4. _Divide product 2 by product 3, and the result is the number of braces, required for the head_.

Table No. 1 gives the total area in square inches. No. 2, areas to be braced. No. 3, number of braces of one inch round iron required, allowing seven thousand five hundred pounds per square inch of section at one hundred pounds steam pressure.

Table No. 3 will be found of more practical use than Table 2, for it gives directly the number of braces required in any given boiler, instead of the area to be braced. It was calculated from Table 2. The iron used in braces will safely stand a continuous pull of 7,500 pounds to the square inch, which is the figure used in computing the foregoing table. A round brace an inch in diameter has a sectional area of .7854 of an inch, and the strain that it will safely withstand is found by multiplying .7854 by 7,500, which gives 5,890 pounds as the safe working strain on a brace of one-inch round iron.

In a 60-inch boiler, whose upper tubes are 28 inches below the shell, the area to be braced is, according to table 2, 930 square inches. If the pressure at which it is to be run is 100 pounds to the square inch, the entire pressure on the area to be braced will be 93,000 pounds, and this is the strain that must be withstood by the braces. As one brace of inch-round iron will safely stand 5,890 pounds, the boiler will need as many braces as 5,890 is contained in 93,000, which is 15.8. That is, 16 braces will be required. The table is made out on the basis of 100 lbs. pressure to the square inch, because that is a very convenient number.

TABLE NO. 1. TOTAL AREA ABOVE TUBES OR FLUES.

(SQUARE INCHES.)

----------+-----------------------------------------
Height | DIAMETER OF BOILER IN INCHES.
from tubes+-----+-----+-----+-----+-----+-----+-----
to shell.| 36 | 42 | 48 | 54 | 60 | 66 | 72
----------+-----+-----+-----+-----+-----+-----+-----
15 | 389 | | | | | |
16 | 419 | | | | | |
17 | 458 | 526 | | | | |
18 | | 566 | 620 | 667 | | |
19 | | 608 | 667 | 720 | | |
20 | | 650 | 714 | 770 | 824 | |
21 | | | 756 | 824 | 882 | |
22 | | | 808 | 878 | 937 | |
23 | | | | 930 | 996 |1059 |
24 | | | | 982 |1056 |1121 |
25 | | | |1037 |1116 |1184 |
26 | | | |1090 |1209 |1252 |1324
27 | | | |1145 |1234 |1316 |1394
28 | | | | |1291 |1381 |1465
29 | | | | |1352 |1445 |1536
30 | | | | |1414 |1511 |1608
31 | | | | | |1576 |1674
32 | | | | | |1641 |1746
33 | | | | | | |1818
34 | | | | | | |1896
----------+-----+-----+-----+-----+-----+-----+-----

TABLE 2. AREAS TO BE BRACED. (SQUARE INCHES.)

----------+-----------------------------------------
Height | DIAMETER OF BOILER IN INCHES.
from tubes+-----+-----+-----+-----+-----+-----+-----
to shell.| 36 | 42 | 48 | 54 | 60 | 66 | 72
----------+-----+-----+-----+-----+-----+-----+-----
15 | 206 | | | | | |
16 | 235 | | | | | |
17 | 264 | 297 | | | | |
18 | | 331 | 365 | 396 | | |
19 | | 316 | 404 | 439 | | |
20 | | 401 | 444 | 483 | 519 | |
21 | | | 485 | 528 | 568 | |
22 | | | 526 | 574 | 618 | |
23 | | | | 620 | 668 | 714 |
24 | | | | 667 | 720 | 769 |
25 | | | | 714 | 772 | 825 |
26 | | | | 761 | 824 | 882 | 937
27 | | | | 809 | 877 | 940 | 998
28 | | | | | 930 | 998 |1061
29 | | | | | 983 |1056 |1124
30 | | | | |1037 |1115 |1187
31 | | | | | |1174 |1252
32 | | | | | |1234 |1317
33 | | | | | | |1382
34 | | | | | | |1447
----------+-----+-----+-----+-----+-----+-----+-----

TABLE 3. NUMBER OF BRACES REQUIRED, AT 100 LBS. PRESSURE.

----------+-----------------------------------------
Height | DIAMETER OF BOILER IN INCHES.
from tubes+-----+-----+-----+-----+-----+-----+-----
to shell.| 36 | 42 | 48 | 54 | 60 | 66 | 72
----------+-----+-----+-----+-----+-----+-----+-----
15 | 3.5 | | | | | |
16 | 4.0 | | | | | |
17 | 4.5 | 5.0 | | | | |
18 | | 5.6 | 6.2 | 6.7 | | |
19 | | 6.2 | 6.9 | 7.5 | | |
20 | | 6.8 | 7.5 | 8.2 | 8.9 | |
21 | | | 8.2 | 9.0 | 9.6 | |
22 | | | 8.9 | 9.8 |10.5 | |
23 | | | |10.5 |11.3 |12.1 |
24 | | | |11.3 |12.2 |13.1 |
25 | | | |12.1 |13.1 |14.0 |
26 | | | |12.9 |14.0 |15.0 |15.9
27 | | | |13.7 |14.9 |16.0 |16.9
28 | | | | |15.8 |16.9 |18.0
29 | | | | |16.7 |17.9 |19.1
30 | | | | |17.6 |18.9 |20.2
31 | | | | | |19.9 |21.3
32 | | | | | |21.0 |22.4
33 | | | | | | |23.5
34 | | | | | | |24.9
----------+-----+-----+-----+-----+-----+-----+-----

In Table 2 this calculation has been made for all sizes of boilers that are ordinarily met with. The area to be braced has been calculated as above in each case, the two-inch strip above the tubes, and the three-inch strip around the shell being taken into account. As an example of its use, let us suppose that upon measuring a boiler we find that its diameter is 54 inches, and that the distance from the upper tubes to the top of the shell is 25 inches. Then by looking in the table under 54″ and opposite 25″ we find 714, which is the number of square inches that requires staying on each head.

BOILER TUBES.

TABLE.

_Dimensions of Lap Welded Boiler Tubes._

--------------+---------+----------
Size outside | Wire |Weight per
diameter. | Gauge. | foot.
--------------+---------+----------
1 inch. | 15 | 0.708
1-1/4 „ | 15 | 0.9
1-1/2 „ | 14 | 1.250
1-3/4 „ | 13 | 1.665
2 „ | 13 | 1.981
2-1/4 „ | 13 | 2.238
2-1/2 „ | 12 | 2.755
2-3/4 „ | 12 | 3.045
3 „ | 12 | 3.333
3-1/4 „ | 11 | 3.958
3-1/2 „ | 11 | 4.272
3-3/4 „ | 11 | 4.590
4 „ | 10 | 5.320
4-1/2 „ | 10 | 6.010
5 „ | 9 | 7.226
6 „ | 8 | 9.346
7 „ | 8 | 12.435
8 „ | 8 | 15.109
9 „ | 7-1/2|
10 „ | 6-1/2|
--------------+---------+----------

The above is the regular manufactures’ list of sizes and weights.

NOTE.

Boiler tubes are listed and described from the _outside diameter_. This should be noted, as gas-pipe is described from the _inside diameter_. Thus a 1-inch gas-pipe is nearly 1-1/4 outside diameter while a 1-inch boiler tube is exactly one inch. Another difference between the two consists in the fact that the outside of boiler tubes is rolled smooth and even; gas-pipe is left comparatively rough and uneven.

When the boiler tubes are new and properly expanded there is a large reserve or surplus of holding power for that part of the tube sheet supported by them, this has been proved by experiment made by chief engineer W. H. Stock, U. S. N., as shown in the following

TABLE OF HOLDING POWER OF BOILER TUBES.

Mr. C. B. Richards, consulting engineer at Colt’s Armory at Hartford, Conn., made some experiments as to the holding power of tubes in steam boilers, with the following results: The tubes were 3 inches in external diameter, and 0.109 of an inch thick, simply expanded into a sheet 3/8 of an inch thick by a Dudgeon expander. The greatest stress without the tubes yielding in the plate was 4,500 pounds, and at 5,000 pounds was drawn from the sheet. These experiments were repeated with the ends of the tubes which projected through the sheet three-sixteenths of an inch, being flared so that the external diameter in the sheet was expanded to 3.1 inches. The greatest stress without yielding was 18,500 pounds; at 19,000 pounds yielding was observed; and at 19,500 pounds it was drawn from the sheet. The force was applied parallel to the axis of the tube, and the sheet surfaces were held at right angles to the tube axis.

NOTE.

When the tube sheet and tube ends near the sheet become coated with scale or the tubes become overheated, the holding power of the tubes becomes largely reduced, and caution must be used in having the tube ends re-expanded and accumulated scale removed.

NOTE 2.—In considering the stress or strain upon the expanded or riveted over ends of a set of boiler tubes, it may be remembered that the strain to be provided against is only that coming upon tube plate, exposed to pressure, _between the tube ends_—the space occupied by the tubes has no strain upon it.

The gauge to be employed by inspectors to determine the thickness of boiler plates will be any standard American gauge furnished by the Treasury Department.

All samples intended to be tested on the Riehle, Fairbanks, Olson, or other reliable testing machine, must be prepared in form according to the following diagram, viz.: eight inches in length, two inches in width, cut out their centres as indicated.

PORTIONS OF THE MARINE BOILER WHICH BECOME THIN BY WEAR.

These are generally situated, 1st, at or a little above the line of fire bars in the furnace; 2d, the ash pits; 3d, combustion chamber backs; 4th, shell at water line; 5th, front and bottom of boiler.

The thinning can usually be detected by examination, sounding with a round nosed hammer, or drilling small holes in suspected parts not otherwise accessible for examination.

EXAMPLES OF CONSTRUCTION AND DRAWING

+--------+--------+---------+---------+
| _d_ | _t_ | _d_ | _t_ |
+--------+--------+---------+---------+
| _9/16″_| _1/4″_ | _15/16″_| _5/8″_ |
+--------+--------+---------+---------+
|_11/16″_| _5/16″_|_1-1/16″_| _3/4″_ |
+--------+--------+---------+---------+
| _3/4″_ | _3/8″_ |_1-1/8″_ | _7/8_ |
+--------+--------+---------+---------+
| _7/8″_ | _1/2″_ |_1-3/16″_| _1″_ |
+--------+--------+---------+---------+
_d_ = DIAM. OF RIVET.

_t_ = THICKNESS OF PLATE.

The small table above is of use in this and the four succeeding pages; in all places in the drawings where “d” is used it indicates _the diameter of the rivet_; “t” means _the thickness of the plate_; “p” stands for _pitch_. The table also shows the proportion of rivet to the plate—thus, a 1/4-inch plate requires a 9/16 rivet, etc.

It is recommended, in view of the increased disposition on the part of official examiners to test the applicant’s knowledge of drawing, for any one interested, to redraw to a _full size_ all the rivets, plates, and methods of joining the two contained on pages 113-116.

The figures 53 to 60 will be understood without much explanation.

In figures 53 and 54 _the cup head, the conical head and pan head rivets_ are shown.

Figs. 55 and 56 exhibit the details (and drawings) of single and double riveting. Where the cut reads p = (2-1/2)d, it means that the distance from the centre of one rivet to the centre of the next shall be 2-1/2 the diameter of the rivet, see example, page 115.

EXAMPLE.

If the size of the rivet used is 7/8ths, then 7/8 × 2-1/2 = 2-2/10 inches nearly, and this gives the proportionate strength of the plate and the rivet, see page 113.

Figs. 57, 58, 59 and 60 show quite clearly the joints and rivet work done in locomotive and marine work. Fig. 60 shows method of riveting 3 plates, A, B, and C, together.

RULE FOR SAFE INTERNAL PRESSURE

The safe internal pressure on cylindrical shells is found according to the following rule, which has been adopted by the United States Board of Supervising Inspectors, and any boiler shell not found in the tables can be determined by this rule.

RULE.—Multiply one-sixth of the lowest tensile strength found stamped on any plate in the cylindrical shell by the thickness—expressed in inches or parts of an inch—of the thinnest plate in the same cylindrical shell, and divide by the radius or half diameter—also expressed in inches—and the result will be the pressure allowable per square inch of surface for single riveting, to which add twenty per centum for double riveting.

The hydrostatic pressure applied, under this table and rule, must be in the proportion of one hundred and fifty pounds to the square inch, to one hundred pounds to the square inch of the working pressure allowed.

EXAMPLE.

What pressure should be allowed to be carried on a boiler 60″ diameter, made of plates 3/8″ thick, having a tensile strength of 60,000 pounds? Now then:

6)60,000
------
10,000
3
------
8)30,000
------
Half diam. 30)3750(125. lbs.--if single riveted.
30
----
75
60
----
150 125 + 25 lbs. (20 feet) = 150 for
150 double riveted.

TABLES SAFE INTERNAL PRESSURE.

----------+---------+---------------+---------------+---------------
| | Pressure. | Pressure. | Pressure.
| +-------+-------+-------+-------+-------+-------
Diameter |Thickness|Single |Double |Single |Double |Single |Double
of | of |Riveted|Riveted|Riveted|Riveted|Riveted|Riveted
Boiler. | Plates. +-------+-------+--------+------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
----------+---------+-------+-------+-------+-------+-------+-------
36 Inches.| .21 | 87.5 |105. | 97.21 |116.65 |106.94 |128.3
| .23 | 95.83 |114.99 |106.47 |127.76 |117.12 |140.54
| .25 |104.16 |124.99 |115.74 |138.88 |127.31 |152.77
| .26 |108.33 |129.99 |120.37 |144.44 |132.4 |158.88
| .29 |120.83 |144.99 |134.25 |161.11 |147.68 |177.21
| .33 |137.5 |165. |152.77 |183.32 |168.05 |201.66
| .35 |145.83 |174.99 |162.03 |194.43 |178.23 |213.87
| .375 |156.25 |187.5 |173.61 |208.33 |190.97 |229.16
+---------+-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,000 Tensile |70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .21 |116.66 |139.99 |126.38 |151.65 |136.11 |163.33
| .23 |127.77 |153.32 |138.41 |166.09 |149.07 |178.88
| .25 |138.88 |166.65 |150.46 |180.55 |162.03 |194.43
| .26 |144.44 |173.32 |156.48 |187.77 |168.51 |202.21
| .29 |161.11 |193.33 |174.53 |209.43 |187.90 |225.48
| .33 |183.33 |219.99 |198.61 |238.33 |213.88 |256.65
| .35 |194.44 |233.32 |210.64 |252.76 |226.84 |272.20
| .375 |208.33 |249.99 |225.69 |271.82 |243.05 |291.66
----------+---------+-------+-------+-------+-------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
| +-------+-------+-------+-------+-------+-------
40 Inches.| .21 | 78.75 | 94.50 | 87.49 |104.98 | 96.24 |115.48
| .23 | 86.25 |103.5 | 95.83 |114.99 |105.41 |126.49
| .25 | 93.75 |112.5 |104.16 |124.99 |114.58 |137.49
| .26 | 97.5 |117. |108.33 |129.99 |119.16 |142.99
| .29 |108.75 |130.5 |120.83 |144.99 |132.91 |159.49
| .3125 |117.18 |140.61 |130.2 |156.24 |143.22 |171.86
| .33 |123.75 |148.5 |137.49 |164.98 |151.24 |181.48
| .35 |131.25 |157.5 |145.83 |174.99 |160.41 |192.49
| .375 |140.62 |168.74 |156.24 |187.48 |171.87 |206.24
+---------+-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,0000 Tensile|70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .21 |105. |126. |113.74 |136.48 |122.49 |146.98
| .23 |115. |138. |124.58 |149.49 |134.16 |160.99
| .25 |125. |150. |135.41 |162.49 |145.83 |174.99
| .26 |130. |156. |140.83 | 68.99 |151.66 |181.99
| .29 |145. |174. |157.08 |188.49 |169.16 |202.99
| .3125 |156.25 |187.45 |169.27 |203.12 |182.29 |218.74
| .33 |165. |198. |178.74 |214.48 |192.49 |230.98
| .35 |175. |210. |189.58 |227.49 |204.16 |244.99
| .375 |187.5 |225. |203.12 |243.74 |218.74 |262.48
----------+---------+-------+-------+-------+-------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
| +-------+-------+-------+-------+-------+-------
42 Inches.| .21 | 75. | 90.00 | 83.32 | 99.99 | 91.66 |109.99
| .23 | 82.14 | 98.56 | 91.23 |109.51 |100.39 |120.46
| .25 | 89.28 |107.13 | 99.2 |119.04 |109.12 |130.94
| .26 | 92.85 |111.42 |103.17 |123.8 |113.49 |136.18
| .29 |103.57 |124.28 |115.07 |138.08 |126.57 |151.85
| .3125 |111.6 |133.92 |124. |148.8 |136.4 |163.68
| .33 |117.85 |141.42 |130.94 |157.12 |144.04 |172.84
| .35 |125. |150. |138.88 |166.65 |152.77 |183.32
| .375 |133.92 |160.7 |148.8 |178.56 |163.68 |196.40
+---------+-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,000 Tensile |70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .21 |100. |120. |108.33 |129.99 |116.66 |139.99
| .23 |109.52 |131.42 |118.65 |142.38 |127.77 |153.32
| .25 |119.04 |142.84 |128.96 |154.75 |138.88 |166.65
| .26 |123.8 |148.56 |134.12 |160.94 |144.44 |173.32
| .29 |138.09 |165.7 |149.6 |179.52 |161.11 |193.33
| .3125 |148.74 |178.56 |161.2 |193.44 |173.61 |208.23
| .33 |157.14 |188.56 |170.23 |204.27 |183.33 |219.99
| .35 |166.66 |199.99 |180.55 |216.66 |194.44 |233.32
| .375 |178.57 |214.28 |193.45 |232.14 |208.33 |249.99
----------+---------+-------+-------+-------+-------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
| +-------+-------+-------+-------+-------+-------
48 Inches.| .21 | 65.62 | 78.74 | 72.91 | 87.49 | 80.2 | 96.24
| .23 | 71.87 | 86.24 | 79.85 | 95.82 | 87.84 |105.4
| .25 | 78.12 | 93.74 | 86.8 |104.16 | 95.48 |114.57
| .26 | 81.25 | 97.50 | 90.27 |108.32 | 99.3 |119.16
| .29 | 90.62 |108.74 |100.69 |120.82 |110.76 |132.91
| .3125 | 97.65 |117.18 |108.5 |130.2 |119.35 |143.22
| .33 |103.12 |123.74 |114.58 |137.49 |126.04 |151.24
| .35 |109.37 |131.24 |121.52 |145.82 |133.67 |160.4
| .375 |117.18 |140.61 |130.2 |156.24 |143.22 |171.86
+---------+-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,000 Tensile |70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .21 | 87.49 |104.98 | 94.79 |113.74 |102.08 |122.49
| .23 | 95.83 |114.99 |103.81 |124.57 |111.8 |133.16
| .25 |104.16 |124.99 |112.84 |135.4 |121.52 |145.82
| .26 |108.33 |129.99 |117.36 |140.83 |126.38 |151.65
| .29 |120.83 |144.99 |130.9 |157.08 |140.97 |169.16
| .3125 |130.21 |156.25 |141.05 |169.26 |151.9 |182.28
| .33 |137.5 |165. |148.95 |178.74 |160.41 |192.49
| .35 |145.83 |174.99 |157.98 |189.57 |170.13 |204.14
| .375 |156.25 |187.50 |169.27 |203.12 |182.29 |218.74
----------+---------+-------+-------+-------+-------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
| +-------+-------+-------+-------+-------+-------
54 Inches.| .21 | 58.33 | 69.99 | 64.81 | 77.77 | 71.29 | 85.54
| .23 | 63.88 | 76.65 | 70.98 | 85.17 | 78.08 | 93.69
| .25 | 69.44 | 83.32 | 77.16 | 92.52 | 84.87 |101.84
| .26 | 72.22 | 86.66 | 80.24 | 96.28 | 88.27 |105.92
| .29 | 80.55 | 96.66 | 89.5 |107.40 | 98.45 |118.14
| .3125 | 86.8 |104.16 | 96.44 |115.72 |106.09 |127.30
| .33 | 91.66 |109.99 |101.84 |122.22 |112.03 |134.43
| .35 | 97.22 |116.66 |108.02 |129.62 |118.82 |142.58
| .375 |104.16 |124.99 |115.74 |138.88 |127.31 |152.77
| +-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,000 Tensile |70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .21 | 77.77 | 93.32 | 84.25 |101.1 | 90.74 |108.88
| .23 | 85.18 |102.21 | 92.28 |110.73 | 99.38 |119.25
| .25 | 92.59 |111.10 |100.3 |120.36 |108.02 |129.62
| .26 | 96.29 |115.54 |104.31 |125.17 |112.44 |134.8
| .29 |107.41 |128.88 |116.35 |139.62 |125.3 |150.36
| .3125 |115.55 |138.66 |125.38 |150.45 |135.03 |162.03
| .33 |122.22 |146.66 |132.4 |158.88 |142.59 |171.10
| .35 |129.69 |155.54 |140.43 |168.51 |151.23 |181.47
| .375 |138.88 |166.65 |150.46 |180.55 |162.03 |194.43
----------+---------+-------+-------+-------+-------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
| +-------+-------+-------+-------+-------+-------
60 Inches.| .21 | 52.5 | 63. | 58.33 | 69.99 | 64.16 | 76.99
| .23 | 57.5 | 69. | 63.88 | 76.65 | 70.27 | 84.32
| .25 | 62.5 | 75. | 69.44 | 83.32 | 76.38 | 91.65
| .26 | 65. | 78. | 72.22 | 86.66 | 79.44 | 95.32
| .29 | 72.5 | 87. | 80.55 | 96.66 | 88.61 |106.33
| .3125 | 78.12 | 93.74 | 86.8 |104.16 | 95.48 |114.57
| .33 | 82.5 | 99. | 91.66 |109.99 |100.83 |120.99
| .35 | 87.5 |105. | 97.22 |116.66 |106.94 |128.32
| .375 | 93.75 |112.5 |104.16 |124.99 |114.58 |137.49
| +-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,000 Tensile |70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .21 | 69.99 | 84. | 75.83 | 90.99 | 81.66 | 97.99
| .23 | 76.66 | 91.99 | 83.05 | 99.66 | 89.44 |107.32
| .25 | 83.83 | 99.99 | 90.27 |108.32 | 97.22 |116.66
| .26 | 86.66 |103.99 | 93.88 |112.65 |101.11 |121.33
| .29 | 96.66 |115.99 |104.72 |125.66 |112.77 |135.32
| .3125 |104.18 |124.99 |112.95 |135.54 |121.52 |145.82
| .33 |109.99 |132. |119.16 |142.99 |128.33 |153.99
| .35 |116.66 |139.99 |126.38 |151.65 |136.11 |163.33
| .375 |125. |150. |135.41 |162.49 |145.88 |174.99
----------+---------+-------+-------+-------+-------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
| +-------+-------+-------+-------+-------+-------
66 Inches.| .1875 | 42.61 | 51.13 | 47.34 | 56.8 | 52.07 | 62.49
| .21 | 42.72 | 57.26 | 53. | 63.63 | 58.33 | 69.99
| .23 | 52.27 | 62.72 | 58. | 69.69 | 63.88 | 76.65
| .25 | 56.81 | 68.17 | 63.13 | 75.75 | 69.44 | 83.32
| .26 | 59.09 | 70.9 | 65.65 | 78.78 | 72.22 | 86.66
| .29 | 65.90 | 79.08 | 73.23 | 87.87 | 80.55 | 96.66
| .3125 | 71. | 85.2 | 78.91 | 94.69 | 86.89 |104.16
| .33 | 75. | 90. | 83.33 | 99.99 | 91.66 |109.99
| .35 | 79.56 | 95.47 | 88.38 |106.05 | 97.22 |116.66
| .375 | 85.22 |102.26 | 94.69 |113.62 |104.16 |124.99
| +-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,000 Tensile |70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .1875 | 56.81 | 68.17 | 61.55 | 73.86 | 66.28 | 79.53
| .21 | 63.63 | 76.35 | 68.93 | 82.71 | 74.24 | 89.08
| .23 | 69.69 | 83.62 | 75.5 | 90.6 | 81.31 | 97.57
| .25 | 75.75 | 90.90 | 82.07 | 98.48 | 88.37 |106.04
| .26 | 78.78 | 94.53 | 85.35 |102.42 | 91.91 |110.29
| .29 | 87.87 |105.44 | 95.2 |114.24 |102.52 |123.02
| .3125 | 84.69 |113.62 |102.58 |123.09 |110.47 |132.56
| .33 | 99.99 |120. |108.33 |129.99 |116.66 |139.99
| .35 |106. |127.27 |114.89 |137.86 |123.73 |148.47
| .375 |113.62 |136.34 |123.1 |147.72 |132.57 |159.08
----------+---------+-------+-------+-------+-------+-------+-------
| |45,000 Tensile |50,000 Tensile |55,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 7,500 | 1-6, 8,333.3 | 1-6, 9,166.6
| +-------+-------+-------+-------+-------+-------
72 Inches.| .1875 | 39.06 | 46.87 | 43.4 | 52.08 | 47.74 | 57.28
| .21 | 43.75 | 52.5 | 48.6 | 58.33 | 53.47 | 64.16
| .23 | 47.91 | 57.49 | 53.24 | 63.88 | 58.56 | 70.27
| .25 | 52.08 | 62.49 | 57.87 | 69.44 | 63.65 | 76.38
| .26 | 54.16 | 64.99 | 60.18 | 72.22 | 66.2 | 79.44
| .29 | 60.41 | 72.49 | 67.12 | 80.55 | 73.84 | 88.60
| .3125 | 65.10 | 78.12 | 72.33 | 86.8 | 79.57 | 95.48
| .33 | 68.75 | 82.5 | 76.38 | 91.62 | 84.02 |100.82
| .35 | 72.91 | 87.49 | 81.01 | 97.21 | 89.11 |106.93
| .375 | 78.12 | 93.74 | 86.8 |104.16 | 95.48 |114.57
| +-------+-------+-------+-------+-------+-------
| |60,000 Tensile |65,000 Tensile |70,000 Tensile
| | Strength. | Strength. | Strength.
| | 1-6, 10,000 | 1-6, 10,833.3 | 1-6, 11,666.6
| +-------+-------+-------+-------+-------+-------
| .1875 | 52.08 | 62.49 | 56.42 | 67.70 | 60.76 | 72.91
| .21 | 53.33 | 69.99 | 63.19 | 75.82 | 68.06 | 81.66
| .23 | 53.88 | 76.65 | 66.21 | 83.05 | 74.58 | 89.43
| .25 | 69.44 | 83.32 | 75.22 | 90.26 | 81.01 | 97.21
| .26 | 72.22 | 86.66 | 78.24 | 93.88 | 84.25 |101.10
| .29 | 80.55 | 96.66 | 87.26 |104.71 | 93.98 |112.77
| .3125 | 86.8 |104.16 | 94.03 |112.88 |101.27 |121.52
| .33 | 91.66 |109.99 | 99.3 |119.16 |106.94 |128.32
| .35 | 97.22 |116.66 |105.32 |126.38 |113.42 |136.1
| .375 |104.16 |124.99 |112.84 |135.43 |121.52 |145.32
----------+---------+-------+-------+-------+-------+-------+-------

DEFINITION OF TERMS.

In the accompanying sections, some of the properties of iron and steel, as employed in the construction of boilers, are given. It is, therefore, desirable that the meanings applied to the various terms used should be clearly understood. The definitions necessary are, then, briefly as follows:—

=Tensile strength= is equivalent to the amount of force which, steadily and slowly applied in a line with the axis of the test piece, just overcomes the cohesion of the particles, and pulls it into separate parts.

=Contraction of area= is the amount by which the area, at the point where the specimen has broken, is reduced below what it was before any strain or pulling force was applied.

=Elongation= is the amount to which the specimen stretches, between two fixed points, due to a steady and slowly applied force, which pulls and separates it into parts. Elongation is made up of two parts: one due to the general stretch, more or less, over the length; the other, due to contraction of area at about the point of fracture.

=Shearing strength= is equivalent to the force which, if steadily and slowly applied at right angles, or nearly so, to the line of axis of the rivet, causes it to separate into parts, which slide over each other, the planes of the surface at the point of separation being at right angles, or nearly so, to the axis of the rivet.

=Elastic limit= is the point where the addition to the permanent set produced by each equal increment of load or force, steadily and slowly applied, ceases to be fairly uniform, and is suddenly, after the point is reached, increased in amount. It is expressed as a percentage of the tensile strength.

=Tough.=—The material is said to be “tough” when it can be bent first in one direction, then in the other, without fracturing. The greater the angles it bends through (coupled with the number of times it bends), the tougher it is.

=Ductile.=—The material is “ductile” when it can be extended by a pulling or tensile force and remain extended after the force is removed. The greater the permanent extension, the more ductile the material.

=Elasticity= is that quality in a material by which, after being stretched or compressed by force, it apparently regains its original dimensions when the force is removed.

=Fatigued= is a term applied to the material when it has lost in some degree its power of resistance to fracture, due to the repeated application of forces, more particularly when the forces or strains have varied considerable in amount.

=Malleable= is a term applied to the material when it can be extended by hammering, rolling, or otherwise, without fracturing, and remains extended. The more it can be extended without being fractured, the more malleable it is.

=Weldable= is a term applied to the material if it can be united, when hot, by hammering or pressing together the heated parts. The nearer the properties of the material, after being welded, are to what they were before being heated and welded, the more weldable it is.

=Cold-short= is a name given to the material when it cannot be worked under the hammer or by rolling, or be bent when cold without cracking at the edges. Such a material may be worked or bent when at a great heat, but not at any temperature which is lower than about that assigned to dull red.

=Hot-short= is when the material cannot be easily worked under the hammer, or by rolling at a red-heat at any temperature which is higher than about that assigned to a red-heat, without fracturing or cracking. Such a material may be worked or bent at a less heat.

=Homogeneous= describes a material which is all of the same structure and nature.

A homogeneous material is the best for boilers, and it should be of suitable tensile strength with contraction of area and elongation best suited for the purpose, having an elastic limit that will insure the structure being reliable; it should be tough and ductile, and its elasticity fairly good, and be capable of enduring strains without becoming too quickly or easily fatigued. The material should be malleable and in some cases weldable; that which is of a decidedly cold-short or hot-short nature should be avoided.

BOILER REPAIRS.

This cut represents a form of clamp used in holding the plates against each other when being riveted.

Fig. 67 represents a peculiar form of bolt for screwing a patch to
a boiler. It is threaded into the boiler plate, the chamfer rests
against the patch and the square is for the application of the
wrench. After the bolt is well in place, the head can be cut off with
a cold chisel.

REPAIRING CRACKS.

Cracks in the crown-sheet or side of a fire-box boiler, or top head of the upright boiler can be temporarily repaired by a row of holes drilled and tapped touching one another, with 3/8 or 1/2 inch copper plugs or bolts, screwed into the plates and afterwards all hammered together.

For a permanent job, cut out the defect and rivet on a patch. This had better be put on the inside, so as to avoid a “pocket” for holding the dirt. In putting on all patches, the defective part must be entirely removed to the solid iron, especially when exposed to the fire.

NOTE.—When fire comes to two surfaces of any considerable extent, the plate next to the fire becomes red-hot and weakens, hence the inside plate, in repairs, must be removed.

The application of steel patches to iron boilers is injudicious. Steel and iron differ structurally and in every other particular, and their expansion and contraction under the influence of changing temperatures, is such that trouble is sure to result from their combination.

DEFECTS AND NECESSARY REPAIRS.

Fig. 68 represents a patch called a “spectacle piece.” This is used to repair a crack situated between the tube ends. These are usually caused (if the metal is not of bad quality) by allowing incrustation to collect on the plate inside the boiler, or by opening the furnace and smoke doors, thus allowing a current of cold air to contract the metal of the plates round the heated and expanded tubes.

The “spectacle piece” is bored out to encircle the tubes adjacent to the crack, or in other words, to be a duplicate of a portion of the tube plate cracked. These plates are then pinned on to the tube covering the crack.

Steam generators, as they are exposed to more or less of trying service in steam production, develop almost an unending number and variety of defects.

When a boiler is new and first set up it is supposed to be clean, inside and out, but even one day’s service changes its condition; sediment has collected within and soot and ashes without.

Unlike animals and plants they have no recuperative powers of their own—whenever they become weakened at any point the natural course of the defect is to become continually worse.

In nothing can an engineer better show his true fitness than in the treatment of the beginnings of defects as they show themselves by well-known signs of distress, such as leaks of water about the tube ends, and in the boiler below the water line, or escaping steam above it. In more serious cases, the professional services of a skillful and honest boiler maker is the best for the occasion.

In a recent report given in by the Inspectors the following list of defects in boilers coming under their observation was reported. The items indicate the nature of the natural decay to which steam boilers in active use are exposed. The added column under the heading of “dangerous” carries its own lesson, urging the importance of vigilance and skill on the part of the engineer in charge.

Nature of Defects. Whole Number. Dangerous.
Cases of deposit of sediment 419 36
Cases of incrustation and scale 596 44
Cases of internal grooving 25 16
Cases of internal corrosion 139 21
Cases of external corrosion 347 114
Broken and loose braces and stays 83 50
Settings defective 129 14
Furnaces out of shape 171 14
Fractured plates 181 84
Burned plates 93 31
Blistered plates 232 22
Cases of defective riveting 306 34
Defective heads 36 20
Serious leakage around tube ends 549 57
Serious leakage at seams 214 53
Defective water gauges 128 14
Defective blow-offs 45 9
Cases of deficiency of water 9 4
Safety-valves overloaded 22 7
Safety-valves defective in construction 41 16
Pressure-gauges defective 211 29
Boiler without pressure-gauges 3 0

This list covers nearly, if not all, _the points of danger_ against which the vigilance of both engineer and fireman should be continually on guard; and is worth constant study until thoroughly memorized.

NOTE.

Probably one-quarter, if not one-third, of all boiler-work is done in the way of repairs, hence the advice of men who have had long experience in the trade is the one safe thing to follow for the avoidance of danger and greater losses, and for the best results the united opinion of 1, the engineer, experienced in his own boiler and 2, the boiler-maker with his wider observation and 3, the owner of the steam plant, all of whom are most interested.

Corrosion is a trouble from which few if any boilers escape. The principal causes of external corrosion arise from undue exposure to the weather, improper setting, or possibly damp brick work, leakage consequent upon faulty construction, or negligence on the part of those having them in charge.

Internal corrosion maybe divided into ordinary corroding, or rusting and pitting. Ordinary corrosion is sometimes uniform through a large portion of the boiler, but is often found in isolated patches which have been difficult to account for. Pitting is still more capricious in the location of its attack; it may be described as a series of holes often running into each other in lines and patches, eaten into the surface of the iron to a depth sometimes of one-quarter of an inch. Pitting is the more dangerous form of corrosion, and the dangers are increased when its existence is hidden beneath a coating of scale. There is another form of decay in boilers known as grooving; it may be described as surface cracking of iron, caused by its expansion and contraction, under the influence of differing temperatures. It is attributable generally to the too great rigidity of the parts of the boiler affected, and it may be looked upon as resulting from faulty construction.

In plugging a leaky tube with a pine plug, make a small hole, of 3/16 of an inch diameter, or less, running through it from end to end. These plugs should never have a taper of more than 1/8 of an inch to the foot. It is well to have a few plugs always on hand. Fig. 69 exhibits the best shape for the wooden plug.

QUESTIONS

BY THE PROPRIETOR TO THE ENGINEER IN CHARGE, RELATING TO CONDITION OF THE BOILER,

How long since you were inside your boiler?

Were any of the braces slack?

Were any of the pins out of the braces?

Did all the braces ring alike?

Did not some of them sound like a fiddle-string?

Did you notice any scale on flues or crown sheet?

If you did, when do you intend to remove it?

Have you noticed any evidence of bulging in the fire-box plates?

Do you know of any leaky socket bolts?

Are any of the flange joints leaking?

Will your safety-valve blow off itself, or does it stick a little
sometimes?

Are there any globe valves between the safety-valve and the boiler?
They should be taken out at once, if there are.

Are there any defective plates anywhere about your boiler?

Is the boiler so set that you can inspect every part of it when
necessary?

If not, how can you tell in what condition the plates are?

Are not some of the lower courses of tubes or flues in your boiler
choked with soot or ashes?

Do you absolutely know, of your own knowledge, that your boiler is in
safe and economical working order, or do you merely suppose it is?

QUESTIONS

ASKED OF A CANDIDATE FOR A MARINE LICENSE RELATING TO DEFECTS IN BOILER WITH ANSWERS.

If you find a thin plate, what would you do?
Put a patch on.

Would you put it on inside or outside?
Inside.

Why so?
Because the action that has weakened the plate will then act on
the patch, and when this is worn it can be replaced; but the plate
remains as we found it.

If the patch were put on the outside, the action would still be on
the plate, which would in time be worn through, then the pressure of
the steam would force the water between the plate and the patch, and
so corrode it; and during a jerk or extra pressure, the patch might
be blown off.

It is on the same principle that mud-hole doors are on the inside.

If you found several thin places, what would you do?
Patch each, and reduce the pressure.

If you found a blistered plate?
Put a patch on the fire side.

If you found a plate at the bottom buckled?
Put a stay through the centre of the buckle.

If you found several?
Stay each, and reduce the pressure.

The crown of the furnace down?
Put a stay through the middle, and a dog across the top.

If a length of the crown were down, put a series of stays and dogs.

A cracked plate?
Drill a hole at each end of the crack; caulk the crack, or put a
patch over it.

If the water in the boiler is suffered to get too low, what may be
the consequence?
Burn the top of the combustion chamber and the tubes; perhaps
cause an explosion.

If suffered to get too high?
Cause priming; perhaps cause the breaking of the cylinder covers.

THE INSPECTION OF STEAM BOILERS.

Let it be clearly understood that if there were no steam generators using steam under pressure _there would he no boiler inspection, and no licensing of engineers_; it requires no license to be a machinist or a machine tender, no more would a license be essential to run a steam engine, except it were connected with the boiler. _The danger to the public arising from their use requires that the care and management of high-pressure steam boilers shall be in hands of careful, experienced and naturally ingenious men_, hence it is on the affairs of the Boiler Room that the first tests are made, as to the worthiness of an aspirant for an engineer’s license, hence, too, the success of many firemen in obtaining the preference over engine-builders or school graduates, in the line of promotion as steam engineers.

The inspection laws of the various states and cities are framed after substantially the same leading ideas, and in presenting one the others may be assumed to be nearly the same.

The special province of the Steam Boiler Inspection and Engineers’ Bureau in the police department in New York City is to inspect and test all the steam boilers in the city, at certain stated periods, and to examine every applicant for the position of engineer as to his ability and qualifications for running an engine and boiler with safety.

According to the laws of the State, every owner, agent or lessee, of a steam boiler or boilers, in the city of New York, shall annually report to the board of police, the location of said boiler or boilers, and, thereupon, the officers in command of the sanitary company shall detail a practical engineer, who shall proceed to inspect such steam boiler or boilers, and all apparatus and appliances connected therewith.

When a notice is received from any owner or agent that he has one or more boilers for inspection, a printed blank is returned to him stating that on the day named therein the boilers will be tested, and he is asked to make full preparation for the inspection by complying with the following rules:

Be ready to test at the above-named time.
Have boiler filled with water to safety-valve.
Have 1-1/4-inch connection.
Have steam gauge.
Steam allowed two-thirds amount of hydrostatic pressure.

More particularly stated, the following have been adopted by one or more Inspection Companies:

HOW TO PREPARE FOR STEAM-BOILER INSPECTION.

1. Haul fires and all ashes from furnaces and ash pits.

2. If time will permit, allow boiler and settings to cool gradually until there is no steam pressure, then allow water to run out of boilers. It is best that steam pressure should not exceed ten pounds if used to blow water out.

3. Inside of boiler should be washed and dried through manholes and handholes by hose service and wiping.

4. Keep safety-valves and gauge-cocks open.

5. Take off manhole and handhole plates as soon as possible after steam is out of boiler, that boiler may cool inside sufficiently for examination; also _keep all doors shut_ about boilers and settings, _except the furnace and ash-pit doors_. Keep _dampers_ open in _pipes_ and _chimneys_.

6. Have all ashes removed from under boilers, and fire surfaces of shell and heads swept clean.

7. Have spare packing ready for use on manhole and handhole plates, if the old packing is made useless in taking off or is burned. The boiler attendant is to take off and replace these plates.

8. Keep all windows and doors to boiler room open, after fires are hauled, so that boilers and settings may cool as quickly as possible.

9. Particular attention is called to Rule 5, respecting doors—which should be open and which closed—also arrangement of damper. The importance of cooling the inside of the boiler by removal of manhole and handhole plates at the same time the outside is cooling, is in equalizing the process of contraction.

ISSUING CERTIFICATES.

These conditions having been complied with, the boiler is thoroughly tested, and if it is deemed capable of doing the work required of it, a number by which it shall hereafter be known and designated is placed upon it in accordance with the city ordinance: Failure to comply with this provision is punishable by a fine of $25. A certificate of inspection is then given to the owner, for which a fee of $2 is paid.

This certificate sets forth that on the day named the boiler therein described was subject to a hydrostatic pressure of a certain number of pounds to the square inch. The certificate tells where the boiler was built, its style or character and “now appears to be in good condition and safe to sustain a working pressure of —— to the square inch. The safety-valve has been set to said pressure.” A duplicate of this certificate is posted in full view in the boiler-room. In case the boiler does not stand the test to which it is subject, it must be immediately repaired and put in good working order before a certificate will be issued.

THE HYDRAULIC TEST.

The hydraulic test is a very convenient method of testing _the tightness of the work in a new boiler_, in conjunction with inspection to a greater or lesser degree, in the passing of new work. As a detector of leakages it has no rival, and its application enables faulty caulking to be made good before the boiler has left the works, and before a leak has time to enter on its insidious career of corrosion. The extent to which it enables the soundness and quality of the work to be ascertained is another matter, and depends on several conditions. It will be evident that if the test be applied with this object to a new boiler, the pressure should range to some point in excess of the working load if such a test is to be of any practical value.

What the excess should be so as to remain within safe limits cannot be stated without regard being paid to the factor of safety adopted in the structure.

In addition to the advantage which the hydraulic test affords as a means of proving the tightness of the riveted seams and work generally, it is also of frequent assistance in determining the sufficiency of the staying of flat surfaces, especially when of indeterminate shape, or when the stresses thrown upon them by the peculiar construction of the boiler are of uncertain magnitude. For the hydraulic test, however, to be of any real value in the special cases to which we refer, it is essential that it should be conducted by an expert, and the application of the pressure accompanied by careful gaugings, so as to enable the amount of bulging and permanent set to be ascertained. Without such readings the application of the test in such cases is worthless, and may be delusive. Indeed, the careful gauging of a boiler as a record of its behavior should be a condition of every test, and is a duty requiring for its adequate performance a skilled inspector.

The duty of inspecting a new boiler or witnessing the hydraulic test properly belongs to one of the regular inspecting companies, who have men in their employ specially trained for the performance of such work. The advantage accruing from such a course is well worth the fee charged for the service, and secures a searching inspection of the workmanship, which frequently brings to light defects and oversights that a mere pumping-up of the boiler would never reveal. Such a proceeding in fact, can only prove that the boiler is water-tight, and a boiler may be tight under test although the workmanship is of the poorest character. Besides, it is well to bear in mind that the tightness of a boiler under test is no guarantee of its tightness after it is got to work. In a word, as far as new boilers are concerned, the application of hydraulic pressure unaccompanied by careful inspection and gaugings may be almost worthless, while with these additions it may be extremely valuable, especially in the case of boilers of peculiar shape, and is a precaution that should not be neglected.

ENGINEERS’ EXAMINATIONS.

Keeping in mind the fact that _if there were no steam-boilers there would be no examinations_ and no public necessity for licenses, these “points” are added.

Examinations are trying periods with all engineers, as the best are liable to fail in their answers from a nervous dread of the ordeal, but the granting of the document is very largely influenced by the personal experience of the candidate in the practical duties of the engine and boiler-room, which must be stated and certified to by the evidence of others.

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Maxims and Instructions for the Boiler RoomChapter V: Introduction (4)

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