HVAC Psychrometric Chart Practice Questions Steel Schedule 40 Fire Protection Guide

Steel Schedule 40 Fire Protection Guide

1. Basic Specifications

Characteristic	Value	Notes
Wall Thickness	0.154" (DN15) to 0.438" (DN300)	Varies by nominal pipe size
Pressure Rating	150-300 psi	Depends on diameter and temperature
Temperature Range	-20°F to 400°F	Beyond 400°F requires derating
Hydrostatic Test Pressure	1.5x working pressure	Minimum 200 psi

⚠ CRITICAL: Schedule 40 steel must be galvanized for wet systems in corrosive environments (NFPA 13 6.1.2).

Nominal Size	Actual ID	Max Flow (GPM)	Velocity Limit
1"	1.049"	30	10 ft/s
2"	2.067"	125	12 ft/s
3"	3.068"	300	15 ft/s
4"	4.026"	500	15 ft/s
6"	6.065"	1,000	20 ft/s

Method	Pressure Rating	Installation Speed	Special Tools Required
Grooved	300 psi	Fastest	Grooving machine
Threaded	150 psi	Slow	Pipe threader
Welded	Full pipe rating	Slowest	Welding equipment
Flanged	250 psi	Moderate	Torque wrench

✓ BEST PRACTICE: Use grooved couplings for most fire protection applications - provides flexibility for seismic movement and easier maintenance.

Pipe Size	Horizontal Spacing	Vertical Spacing	First Hanger from Fitting
1"-1½"	10 ft	15 ft	24"
2"-3½"	12 ft	18 ft	36"
4"-6"	14 ft	21 ft	48"
8"+	16 ft	24 ft	60"

Environment	Protection Method	Inspection Frequency
Dry Systems	Primer + approved paint	Annually
Wet Systems	Hot-dip galvanizing	Every 5 years
High Humidity	Epoxy coating	Every 3 years
Underground	Wrapped + cathodic protection	Every 10 years

⚠ WARNING: Never mix galvanized and black steel without dielectric separation - will accelerate corrosion.

Hazen-Williams formula for Schedule 40 steel (C=120):

P_f = (4.52 × Q^1.85) / (C^1.85 × d^4.87)

Where:
P_f = Friction loss (psi/ft)
Q = Flow (GPM)
C = Hazen-Williams coefficient (120 for new steel)
d = Actual inside diameter (in)

Reference Standards: NFPA 13 (2022 Ed.), ASTM A53/A106, MSS SP-58