STAMP Method for Fitting Selection: Size, Temperature, Application, Media, Pressure
Jan 3rd 2024
The STAMP method is a practical way to select fittings for fluid and gas systems. It stands for Size, Temperature, Application, Media, and Pressure.
Fittings and adapters hold and seal hoses, tubes, pipes, manifolds, ports, valves, pumps, and cylinders. A correct connection can provide long leak-free service even with high temperature, high pressure, corrosion, and vibration.
Connection Type Comes First
Fitting connections generally seal in two broad ways: metal seal connections and O-ring or other soft seal connections.
Metal seals depend on matching metal surfaces such as flares or cones. Soft seals depend on an elastomer or similar sealing material. The STAMP checks help determine which style is suitable.
Size
Size begins with tube outside diameter and wall thickness. These are selected from system pressure, flow rate, temperature, ambient conditions, and fitting specifications.
Some flare fittings have a maximum tube wall thickness limitation. Some flareless bite-type fittings need a minimum wall thickness so the fitting can grip and seal the tube correctly.
Temperature
Temperature capability depends on both fitting material and seal material. Aluminum and brass are commonly used across moderate temperature ranges, while stainless steel can be used across much wider ranges when the fitting design supports it.
Seal compounds also vary. EPDM, fluorocarbon, and nitrile each have different temperature and media limits. The seal must match both the system temperature and the fluid.
Application
The application drives the full selection. Hydraulic fluid, fuel, steam, CNG, LNG, and hazardous chemical service all create different requirements.
Corrosive environments may require stainless steel or specialty alloys. Steel may use protective coating, and brass may fit certain lower-pressure or corrosive conditions, but the severity of the application should guide the choice.
Media
The fluid or gas must be compatible with the fitting, tube, hose, and seal. Chemical compatibility is not optional because the media can swell, harden, dissolve, or corrode materials.
When a system changes fluid, the fittings and seals should be reviewed again. A fitting that was correct for one media may be wrong for another.
Pressure
The fitting pressure rating must meet or exceed the required system pressure. Many tube fittings are rated with a 4:1 design factor under normal operating conditions to account for pressure fluctuation and shock.
Pressure capability depends on tube wall thickness, tube or hose rating, fitting style, material, media, and torque. An under-torqued or over-torqued fitting can fail even when the catalog pressure rating looks sufficient.
Using STAMP in Practice
STAMP is most useful when all five checks are considered together. Size without pressure is incomplete. Pressure without media compatibility is unsafe. Temperature without seal review can still leak.
Record the five details before ordering replacement fittings or changing a system connection.