Nternational standard system and size parameters
Stainless steel sizes are usually determined by outer diameter and wall thickness. ASME B36.19 standard 23 is the size standard for stainless steel pipes. This standard specifies the standardized parameters for welded (seamless) steel pipes under high temperature, high pressure and low temperature environments. There are the following core standards:
NPS (Nominal Pipe Size)
In inches as the basic unit (1/8″ to 24″) The core standard for North American pipe sizes. This standardization system is established with reference to the outer diameter parameter.
DN (Diameter Nominal)
The most international metric standard, metric diameter nominal, in millimeters, and corresponding to NPS (e.g. DN15 corresponds to NPS 1/2″)
SCH (Schedule Number)
Wall thickness grade code, calculated by formula, divided into two series: conventional (SCH 5-160) and special (SCH 5S/10S/40S/80S).
Matching SCH grade with wall thickness
SCH value represents the standardized sequence of pipe wall thickness, and pressure bearing capacity also affects the calculation results
The formula is as follows:
SCH = (P × D)/(2 × S × E) + CA
(Where P is pressure, D is outer diameter, S is material strength, E is welding coefficient, and CA is corrosion allowance)
Some commonly used SCH grade application scenarios in steel chart:
|
SCH grade |
Applicable pressure range |
Typical material |
|
SCH 5S |
Low pressure system |
304/316L |
|
SCH 10S |
Conventional pipeline |
304/316 |
|
SCH 40S |
High pressure system |
316Ti/904L |
Conversion between metric and imperial systems
In engineering practice, the following conversion relationships should be noted:
- Outer diameter comparison
NPS 1/2″ = DN15 ≈ 21.3mm (the actual value is retained to one decimal place) - Wall thickness conversion
SCH 40S has different wall thicknesses in different pipes. The wall thickness of DN50 pipe is 3.91mm, while that of DN100 is 4.19mm.
3 Tolerance range - The tolerance of welded pipes is usually ±15%, and the deviation of seamless pipes is slightly smaller than that of welded pipes, usually ±12.5%.
Material selection and standard association
Parameter combinations that require special attention in the stainless steel pipe steel chart:
ASTM A312: General standard for austenitic stainless steel
ASTM A358: Specification for arc-welded stainless steel pipes
JIS G3459: Japanese standard for high-pressure pipelines
Dimensional adaptability differences of different steel grades:
304/316 series: Applicable to SCH 5S-80S
Duplex steel (2205/2507): SCH 10S or higher is recommended
Ultra-low carbon steel (316L): SCH 40S or higher is preferred
