secured to the stayed plate. (See figure 52.35-1 (e).)

(f) Crowfoot. Crowfoot is a forged fitting with palms or lugs secured to the head to form a proper connection with a sling stay. (See figure 52.35-1 (f).)

(g) Crowfoot stay. Crowfoot stay is a solid bar stay terminating in a forged fork with palms or lugs for attachment to the plate. (See figure 52.35-1 (g).)

(h) Diagonal stay. Diagonal stay is a bar or formed plate forged with palms or lugs for staying the head of the boiler to the shell diagonally. (See figure 52.35-1 (h).)

(i) Gusset stay. Gusset stay is a triangular plate used for the same purpose as a diagonal stay and attached to the head and the shell by angles, flanges, or other suitable means of attachment. (See figure 52.35-1 (i).)

(j) Dog stay. Dog stay is a staybolt, one end of which extends through a girder, dog, or bridge, and is secured by a nut, the other end being screwed through the plate which it is supporting and riveted over or fitted with a nut or welded collar. (See figure 52.35–1 (j).)

(k) Girder. Girder is a bridge, built up of plates or structural shapes separated by distance pieces, a forging, or a formed plate, which spans an area requiring support, abutting thereon and supporting the girder stays or staybolts. (See figure 52.35-1 (k).)

(1) Welded collar. Welded collar is a beveled ring formed around the end of a screw stay by means of arc or gas welding. It is used in lieu of a nut. (See figure 52.35-1 (1).)

(m) Reinforcement. Reinforcement is a doubling plate, washer, structural shape, or other form for stiffening or strengthening a plate.

(n) Stay tube. Stay tube is a thickwalled tube used in fire-tube boilers to stay the tube sheets.

(0) Telltale hole. Telltale hole is a small hole having a diameter not less than 16 inch drilled in the center of a solid stay and extending to at least 2 inch beyond the inside surface of the sheet.

§ 52.35-5 Materials. (a) Round bar stays which require no welding or forg

ing other than upsetting at the ends for threading or to form eyes for use in conjunction with crowfeet, or similar fastenings, shall conform to the requirements of Subpart 51.07, 51.10, or 51.13 of this subchapter.

(b) Crowfeet, lugs, and similar connections for stays shall be forgings without welds conforming to the requirements of Subpart 51.46 of this subchapter.

(c) Forged-welded stays or parts parts thereof shall conform to the requirements of Subpart 51.13. All welds in the body of the stay shall be made by the hammer-weld process.

(d) Stiffeners made of structural shapes shall conform to the requirements specified in Subpart 51.10 of this subchapter.

(e) Gusset and diagonal stays made of steel plate, also doubling plates and girders shall conform to the requirements specified in Subpart 51.04 of this subchapter.

(f) Stay tubes shall conform to the requirements of Subpart 51.25, 51.28, or 51.31 of this subchapter.

(g) Rivets shall conform to the following requirements: Steel rivets__. Iron rivets...

Subpart 51.16 Subpart 51.19

(h) Nuts for screw stays shall be made of steel, conforming to the requirements of Subpart 51.46 or 51.55, or, refined wrought iron, conforming to the requirements of Subpart 51.13 of this subchapter.

§ 52.35-10 Workmanship. (a) The ends of stay bars and stay tubes which are upset for threading shall be subsequently annealed.

(b) Holes for screw stays shall be drilled and tapped fair and true and shall have a full thread.

(c) All holes for rivets shall be drilled and shall be slightly counter-sunk in order to form a fillet at point and head. Rivets shall be of sufficient length to fill the rivet holes completely and to form a head of proportionate strength to the body of the rivet.

(d) Holes for tubes or through stays may be made by punching a pilot hole in the center, but shall be machined to size by a rotating cutter, or otherwise be drilled from the solid plate.

(e) When jointed longitudinal stays are fitted between the back and front tube plates and connected by pins, such pins may be fitted slack in the holes, but the total clearance on both ends shall not exceed 16 inch.

(f) Where stay tubes are used for supporting flat surfaces they shall be fitted with threads at both ends, screwed into the tube sheets and rolled tight with expanders, in addition to which they may be beaded. Making such tubes tight by calking is not permissible.

§ 52.35-15 Computations. (a) The maximum allowable pressure and the required area of direct stays shall be computed by the following formulas (in making computations, the least sectional area of the stay shall be taken):

C-9,000 for solid steel screw stays
having diameters of 1 inch
and above.

C-9,000 for jointed steel stays.
C=8,000 for solid or hollow steel

screw staybolts having diam-
eters of 1 inch or less.
C-8,000 for refined wrought-iron
stays or staybolts having di-
ameters of 1 inch and above.
C-8,000 for steel stays formed from
plates without welds.
C-7,500 for wrought-iron or steel
stay tubes.

C-7,500 for flexible screw staybolts.
C=7,500 for refined wrought-iron
screw staybolts having diam-
eters less than 1 inch.
C-6,000 for welded refined wrought-
iron stays.

(b) In computing the gross area supported by a stay, the pitch of the stays shall be used, but the least sectional area of the stay may be deducted therefrom to obtain the net area.

(c) Where stays are adjacent to the outer edge of the surface to be stayed and special allowances are made for the spacing, the area A shall be determined by deducting such parts of the surface as may be considered self supporting in accordance with § 52.30-5.

(d) The required cross-sectional area of a diagonal stay shall be determined by the following formula:

where:

=

a, required area of diagonal stay, in square inches.

a- required area of direct stay computed by formula (2) in this section, in square inches.

L= lengh of diagonal stay as shown by figure 52.35-1 (h), in inches. l-length of line drawn at right angles to the surface to be supported, and extending to the center of the first rivet in the diagonal stay as shown by figure 52.35-1 (h), in inches. (e) The minimum sectional area of a gusset stay constructed of triangular plates secured to single or double rolled shapes along the two sides, shall be 10 percent greater than that determined by formula (3) in this section for diagonal stays.

(f) In determining the net crosssectional area of drilled or hollow staybolts, the cross-sectional area of the hole shall be deducted if the diameter exceeds 3/16 inch.

(g) Where a cylindrical shell is pierced by more than three holes for stays or other purposes on a line parallel with the axis of the shell, the relative strength of the ligaments between such holes shall not be less than that of the ligaments in the outer row of rivets in the logitudinal joint. If the construction necessitates a lower relative strength, this must be used for the value of E in the formula (1), (2), or (3) in § 52.05-10, for determining the maximum allowable pressure or minimum thickness of

plate.

(h) The minimum sectional area of a pin subject to double shear shall be at least 80 percent of the required crosssectional area of the stay.

(i) Each branch of a crowfoot or similar component part of a divided stay shall be proportioned to support at least two-thirds of the entire load.

(j) Eyes for pin connections shall be properly formed to the body of the stays. The minimum outside diameter of the eye shall be one and one-fourth times that of the pin. The minimum thickness of a single eye shall be the diameter of the pin; that of the double eye shall be two-thirds of the diameter of the pin; the cross-sectional area of any part of an eye shall be such that the two sides of a single eye shall equal at least one and one-fourth, and the four sides of a forked eye shall equal at least one and one-half times the strength of the body of a stay.

(k) The strength of the rivets connecting crowfoot braces, or any other type of reinforcement, shall equal one and one-half times the strength of the connecting stay.

(1) Palms, lugs, or flanges which are to be riveted, shall have a minimum width at the rivet hole exceeding the diameter of the rivet head, and shall have a cross-sectional area exclusive of the rivet hole not less than one and onefourth times the required cross-sectional area of the body of the stay. Where there are two or more rivets located in the longitudinal axis of the stay, the strength of the palm or lug at the second or subsequent rivet hole may be reduced to not less than one and one-fourth times the combined strength of the rivet at that point and those beyond.

§ 52.35-20 Detail requirements. (a) All screw staybolts, except flexible staybolts, shall have a telltale hole in the center of each end not less than 3/16 inch diameter extending not less than 1/2 inch beyond the inside of the plate.

(b) Joining of steel stays in the body by any process of welding is not permissible.

(c) The length of staybolts shall not exceed 20 diameters.

(d) Where the length of a boiler exceeds 18 feet, the through stays shall be supported in the middle.

(e) Where the heads of staybolts are riveted over, the end of the staybolt before riveting shall extend not less than 1/4 inch from the surface of the plate to provide sufficient material for a substantial head,

(f) Where welded collars are used instead of nuts, the depth of the collar,

§ 52.40-1 Definitions (a) Curved tube sheet. Curved tube sheet is a section of the shell of a boiler drum formed to an arc of a circle and perforated for nests of tubes.

(b) Flat tube sheet. Flat tube sheet is the tube plate of box headers of certain types of water-tube boilers.

(c) Longitudinal ligament. Longitudinal ligament is the minimum section of metal between two tube holes on a line parallel with the axis of the drum.

(d) Circumferential ligament. Circumferential ligament is the minimum section of metal between two tube holes on a line around the circumference of the drum.

(e) Diagonal ligament. Diagonal ligament is the minimum section of metal between two tube holes in adjacent rows, measured diagonally from one row to the other.

§ 52.40-5 Computations for curved tube sheet. (a) The maximum allowable pressure and minimum thickness of a curved tube sheet shall be determined by formula (1), (2), or (3) in § 52.05-10, using the lowest value of E, derived as follows:

(b) When a shell is pierced for a single row of tubes or for two or more rows well apart, as in a double butt-strap joint, or where reinforcing plates are fitted, the efficiency of the ligament between tube holes shall be determined by formula (1) in § 52.05-25 (b).

(c) When a shell is pierced for tubes in a series of rows parallel to its axis, the efficiency of the ligament between the tube holes in any row shall be determined according to the provisions of this section.

this line horizontally to the left on the edge of the diagram the diagonal efficiency of the ligament may be read from the scale. If this efficiency is less than that of the longitudinal ligament it shall be used in computing the allowable pressure. The symbols used in the above formulas are as follows:

p= longitudinal pitch of tube holes, in inches.

=

diagonal pitch of tube holes, in inches. length of section of the row considered, in inches.

d diameter of tube holes, in inches. n = number of tube holes in section p1. (2) The pitch of the tube holes shall be measured either on the flat plate before rolling or on the middle line of the plate after rolling.

(g) The strength of the circumferential ligaments between tube holes shall be at least one-half the required strength of the longitudinal ligaments.

(h) When the tube holes are not normal to the plate, the plate thickness shall be sufficient to provide a parallel seating not less than % inch in depth between planes at right angles with the axis of the tube for tubes 21⁄2 inches in diameter and under; for tubes having diameters over 21⁄2 inches, the depth of the parallel seating shall be not less than 1⁄2 inch.