Overview
ASME B16.4 covers dimensions, ratings, and tolerances for gray iron threaded fittings. These are low-pressure fittings relegated to applications where the improved ductility of malleable iron (B16.3) is not required and extreme cost-savings are the primary goal.
Scope & Applicability
Applies To Industries
Covers — gray iron threaded fittings:
- Sizes from NPS 1/4 to NPS 12.
- Pressure classes: Class 125 and Class 250.
- Fittings: Elbows, tees, crosses, and returns.
Does NOT cover (exclusions) — the following are governed elsewhere:
- Malleable iron fittings (much higher ductility) → ASME B16.3.
Key Requirements
Because gray iron is metallurgically brittle (containing flake graphite that acts as stress risers), B16.4 fittings have strict temperature and pressure limitations. They are generally confined to non-shock, non-hazardous ambient temperature applications.
Technical Details
While once common in older buildings, gray iron threaded fittings have largely been superseded by malleable iron (B16.3) in general construction.
Malleable iron offers significantly better resistance to cracking if a pipefitter over-tightens the joint or if the pipe settles and induces bending stress. Because the cost difference between cast gray iron and malleable iron has become marginal, most modern projects default to B16.3 to avoid installation breakages.
Engineering Notes
ASME B31.3 and other process codes strictly prohibit the use of gray iron fittings (B16.4) in hydrocarbon, toxic, flammable, or high-vibration systems due to the massive risk of catastrophic, unpredictable brittle failure.
Source, Edition & Status
- Publisher
- ASME
- Industries
- Waterworks, General Industry
- Last Reviewed
- 2026-07-01
- Last Updated
- 2026-07-01
- Verified By
- Engineering content reviewer
- Content Status
- reviewed