# How To: Determine Stayed Surface Calculations

The lesson we are going to learn today is How To: Determine Stayed Surface Calculations. This post will review the formula(s) provided in the Boiler & Pressure Vessel Code, along with one formula that is not provided. Define the different variables used in each formula. Wrapping it up by reviewing numerous practice questions.

All referenced page numbers are from the 2007 ASME Boiler & Pressure Vessel Code

## Formulas

PG-46.1 page 26 The minimum thickness, maximum allowable working pressure, and pitch for stayed flat plates and those parts that, by these rules, require staying as flat plates with stays or stay bolts of uniform diameter symmetrically spaced, shall be calculated by the following equations:

Minimum Required Thickness Formula

Maximum Allowable Pressure Formula

Determining The Pitch Formula

The above formula to calculate the pitch for a stayed surface is not provided in the 2007 ASME Boiler & Pressure Vessel Code

## Formula Variables

The variables used in the formulas provided above to determine stayed surface calculations are defined in PG-46.1 page 26/27 as follows:

C = 2.1 for welded stays or stays screwed through plates not over 7/16 in. (11mm) in thickness with ends riveted over

= 2.2 for welded stays or stays screwed through plates over 7/16 in. (11mm) in thickness with ends riveted over

= 2.5 for stays screwed through plates and fitted with single nuts outside of plate, or with inside and outside nuts, omitting washers

= 2.8 for stays with heads not less than 1.3 times the diameter of the stays screwed through plates or made a taper fit and having the heads formed on the stay before installing them, and not riveted over, said heads being made to have a true bearing on the plate

= 3.2 for stays fitted with inside and outside nuts and outside washers where the diameter of washers is not less than 0.4p and thickness is not less than t

P = Maximum allowable working pressure, psi (MPa)

p = Maximum pitch measured between straight lines passing through the centres of the staybolts in the different rows, which lines may be horizontal and vertical, or radial and circumferential, in (mm)

S = Maximum allowable stress value given in Table 1A of Section II, Part D, psi (MPa)

t = Minimum thickness of plate, in. (mm)

[table id=1 /]

## How To: Determine Stayed Surface Calculations Questions

Note: All code questions are to be calculated in (mm) and (MPa) unless otherwise stated. Convert accordingly and properly before the calculation.

## Summary

You should familiarize yourself with all stayed surface requirements when completing calculations. The ones listed below, are the ones I found most important when completing questions.

• PFT-22 Stayed Surfaces page 95 The rules Parts PG and PW pertaining to stays and stayed surfaces that are applicable to firetube boilers shall be used in conduction with the following requirements.
• PG-46.2 page 27 The minimum thickness of plates to which stays may be applied, in other than cylindrical or spherical outer shell plates, shall be 5/16 in. (8mm), except for welded construction covered by PW-19.
• PG-46.5 page 27 The maximum pitch shall be 8 1/2 in. (215mm) except that for welded-in stay bolts the pitch may be greater provided it does not exceed 15 times the diameter of the staybolt.

What other requirements do you find important when completing How To: Determine Stayed Surface Calculations?

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