Am I understanding the following PG.29.3 section of the code correctly.
"When a head, dished to a segment of a sphere, has a flanged-in manhole or access opening that exceeds 150 mm in any dimension, the thickness shall be increased by not less than 15% of the required thickness for a blank head computed by the above formula, but in no case less than 3 mm additional thickness over a blank head. Where such a dished head has a flanged opening supported by an attached flue, an increase in thickness over that for a blank head is not required. If more than one manhole is inserted in a head, the thickness of which is calculated by this rule, the minimum distance between the openings shall be not less than one-fourth of the outside diameter of the head."
I am only concerned with the bold section.
Are they saying that only access opening must exceed 150mm? Flanged-in manhole is exempt from this dimension?
The reason why I believe they are separate is because of the following paragraph.
Paragraph PG-44 specifies that boilers have suitable openings, such as manholes, handholes, inspection openings, and washout openings. Elliptical manholes shall not be less than 300 × 400 mm in size. Circular manholes shall not be less than 380 mm in diameter. Handholes shall not be less than 70 mm × 89 mm. There are no specific dimensions for other inspection or washout openings.
Inherently the flanged in man-hole will indeed be bigger than 100mm according to the above.
Thank you for your help.