While completing ASME code calculations involving cylindrical components for 3rd Class Power Engineering you’ll be required to know how to calculate the maximum allowable working pressure of a boiler drum.

The referenced page numbers below are from the **2007 ASME Boiler & Pressure Vessel Code.**

## Formula

To calculate the maximum allowable working pressure of a boiler drum during different operating conditions you can use the formula contained within ASME Boiler & Pressure Vessel Code PG-27 Cylindrical Components Under Internal Pressure *page 10*. Specifically, PG-27.2.2 *page 10*

**PG-27.2.2 Piping, Drums, and Headers. (based on strength of weakest course)** *It is important to remember any cylinder with an outside diameter less then 125mm is to be considered tubing and the equation provided in PG-27.2.1 page 8 should be used.*

**PG-27.2.2 Formula to calculate the maximum allowable working pressure for a boiler drum:**

**Outside Diameter Equation**

**Inside Radius Equation**

## Formula Variables

The symbols used within the PG-27 formulas are contained within paragraph PG-27.3 *page 10* and are defined as follows:

C = Minimum allowance for threading and structural stability (mm) (PG-27.4, note 3) *page 11*

D = Or O.D. is Outside diameter of cylinder (mm)

E = Efficiency of longitudinal welded joints or of ligaments between openings, whichever is lower (the values allowed for E are listed in PG-27.4, note 1) *page 11*

e = Thickness factor for expanded tube ends (mm) (see PG-27.4, note 4) *page 11*

P = Maximum allowable working pressure “Gauge Pressure” (MPa) (see PG-21, refers to gauge pressure)

R = Inside radius of cylinder (mm) “In this case a boiler drum”

S = Maximum allowable stress value at the operating temperature of the metal (Section II, Part D, Table 1A. See PG-27.4, note 2) *page 11*. It is important when determining the maximum allowable stress value to check (PG-6 plate materials) *page 4* and (PG-9 boiler tube materials) *page 5* before starting calculations as this information will determine the correct stress table to use by indicating whether the material is carbon steel or an alloy steel.

t = minimum required thickness (mm) (see PG-27.4, note 7) *page 12*

y = temperature coefficient (see PG-27.4, note 6) *page 11*

## How To: Calculate The Maximum Allowable Working Pressure Of A Boiler Drum Questions

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

How To Determine The Maximum Allowable Working Pressure Of A Boiler Drum Question #11

How To Determine The Maximum Allowable Working Pressure Of A Boiler Drum Question #12

## Summary

Hopefully the examples provided helped you understand how to calculate the maximum allowable working pressure of a boiler drum. If you have additional questions, feedback, or ideas about the content provided please let me know in the comments below.

Thanks,

Power Engineering 101