Section 8 Headers

8.1.1 The minimum thickness of circular section headers is to be calculated in accordance with the formula for cylindrical shells in Vol 2, Pt 8, Ch 1, 2.1 Minimum thickness.

8.2.1 The thickness of the flat walls of rectangular section headers is to be determined at the centre of the sides, at all the lines of holes and at the corners. The minimum required shall be the greatest thickness determined by the following formula:

where t, p, c and σ are as defined in Vol 2, Pt 8, Ch 1, 1.2 Definition of symbols

8.2.2 The coefficient Y for use in Vol 2, Pt 8, Ch 1, 8.2 Rectangular section headers 8.2.1 is to be determined as follows:

1. at the centre of the side with internal width, 2m:

   

   where

   m

   =

   one half of the internal width of the wall under consideration, in mm, see Figure 1.8.1 Rectangular section headers(b)

2. at a line of holes parallel to the longitudinal axis of the header on the wall of width, 2m:

   

   where

   b

   =

   distance from the centre of the holes to the centre line of the wall, in mm, see Figure 1.8.1 Rectangular section headers(a)

3. to check the effect of the off-set on a staggered hole arrangement where the holes are positioned equidistant from the centre line of the wall:

   

   where

   α

   =

   the angle subtended by the diagonal ligament on the longitudinal ligament, see Figure 1.8.1 Rectangular section headers(a)

4. at the corners:

   

8.2.3 The ligament efficiencies, J and J ₁, are to be determined as follows:

1. for a line of holes parallel to the longitudinal axis of the header:

   

2. for the diagonals:

   

3. for a line of holes parallel to the longitudinal axis of the header:

   

   or

   

4. for the diagonals:

   

   or

   

   where

   d

   =

   diameter of the hole in the header, in mm

   m, s and s ₁, in mm, are as shown in Figure 1.8.1 Rectangular section headers

8.2.4 In the case of elliptical holes the value of d to be used in the equations for J and J ₁ is to be the inside dimension of the hole measured parallel to the longitudinal axis of the header. For evaluating the two limiting values of d in the equations for d ₁, the value of d is to be the inside dimension of the hole measured perpendicular to the longitudinal axis of the header.

8.2.5 The internal corner radius, r, is to be not less than one third of the mean of the nominal thicknesses of the two sides, but in no case to be less than 6,5 mm.

8.3.1 The minimum thickness of a toroidal header forming the lower end of a waterwall furnace, and supporting the weight of the boiler and water, is to be determined by the following formula:

where

t, p, c and σ are as defined in Vol 2, Pt 8, Ch 1, 1.2 Definition of symbols

where

The calculation is to be performed at design pressure using the allowable stress at saturation temperature, and also at zero pressure using the allowable stress at 100°C.

8.4.1 The shape and thickness of ends forged integrally with the bodies of headers are to be the subject of special consideration.

8.4.2 Where sufficient experience of previous satisfactory service of headers with integrally forged ends cannot be shown, the suitability of a proposed form of end is to be proved in accordance with the provisions of Vol 2, Pt 8, Ch 1, 1.10 Pressure parts of irregular shape

8.4.3 Ends attached by welding are to be designed as follows:

• Dished ends: these are to be in accordance with Vol 2, Pt 8, Ch 1, 4.1 Minimum thickness
• Flat ends: the minimum thickness of flat end plates is to be determined by the following formula:

where p, c and σ are as defined in Vol 2, Pt 8, Ch 1, 1.2 Definition of symbols

For end plates welded as shown in Figure 1.8.3 Typical methods of attachment of header end closures(a):

For end plates welded as shown in Figure 1.8.3 Typical methods of attachment of header end closures(b) and (c):

8.4.4 Where flat end plates are bolted to flanges attached to the ends of headers, the flanges and end plates are to be in accordance with recognised pipe flange standards.

8.4.5 Openings in flat plates are to be compensated in accordance with Figure 1.2.9 Compensation for welded standpipes or branches in cylindrical shells(a) or (b), with the value of A ₁ the compensation required, calculated as follows:

where

Limit D = 0,5d _o.