For welded Lancashire, Cornish and cylindrical horizontal multi-tubular type boilers, all welded gusset stays shall not be used. To ensure flexibility, link stays, bar stays, brace stays and other similar stays or suitably designed gusset stays other than the all-welded type shall be used. All welded gusset stays, however, may be used in cylindrical horizontal waste heat and cylindrical vertical multitubular boilers.

Welded gusset stays and braces may be used for welded Lancashire, Cornish and Cylindrical Horizontal Multi-tubular boilers provided their method of attachment is approved by the Inspecting Authority.

Each gusset or link stay supporting the flat end plate of a boiler shall be designed to carry the whole load due to pressure on the area it supports. The area supported by any one stay shall be obtained by considering the total area to be supported which lies within the limits of the flat plate margins and dividing this area by boundary lines drawn between the stays. These boundary lines shall be at all points equidistant from the adjacent points of support in the area under consideration.

The effective uniformly distributed load on a triangular gusset plate or on a diagonal link stay shall be assumed to be equal to the perpendicular load on the portion of the end plate to be supported (determined as above) multiplied by L/L₁ (see Figs. XII/81, XII/82, XII/83).

Gusset plates shall be so proportioned that the angle “V”  (see Figs. XII/81 and XII/82), is not less than 60°.

The thickness of the gusset plate shall be such that the stress in the plate to withstand the effective uniformly distributed load (as defined above) calculated on the smallest cross-section on Line XX or YY (Figs. XII/81 and XII/82, shall not exceed one-seventh of the minimum tensile stress of the plate used but in no case shall be the thickness be less than seven-eighths of the thickness of the shell plate with a minimum of 7/16 inch.

Where all-welded gusset stays are used a stiffening plate shall be welded at the toe of the gusset where it is secured to the end plate (i.e., where the maximum stress occurs) (see Fig. XII/81).