Technical Documentation: Pressure Standards for Piping, Valves, and Instrumentation

This article clarifies the connections between kilogram-force pressure, pound class, PSI and nominal pressure, details different pressure standards, and explains unit conversions and application.

Jan 9th,2026 118 Views

Technical Documentation: Pressure Standards for Piping, Valves, and Instrumentation
1. Introduction

In the design, procurement, and construction of components such as piping, valves, and instrumentation, terms like "how many kilograms of pressure", "how many pound classes", and "how many PSI" are frequently used. These terms are closely related to pressure units and are inherently linked to "nominal pressure". This document clarifies the connections between these concepts, details different pressure standards, and explains unit conversions and application notes.

2. Nominal Pressure (PN) and Class (American Standard Pound Class)

2.1 Definition and Representation

Nominal Pressure (PN): A pressure representation method primarily used in the Chinese and European systems. It consists of the letter "PN" followed by a dimensionless number (the number has no unit and serves only as a specific symbolic identifier). For example, PN 16, PN 25.

Class (American Standard Pound Class, Lb): A pressure representation method used in the American system. It is denoted by the word "Class" (or abbreviation "CL") followed by a dimensionless number, which can also be written as "LB" (e.g., Class 900 or 900LB). The number here is also dimensionless.

Japanese Pressure Classification: Japan mainly uses the "K-class" to indicate pressure levels (e.g., 10K, 20K, 30K).

2.2 Temperature Baseline Differences (Critical for Engineering Application)

A key note is that Class (pound class) and PN (nominal pressure) are not in one-to-one correspondence, primarily due to their different temperature baselines:

PN System:

European system: Refers to the pressure corresponding to 120°C.

Chinese system: Refers to the pressure corresponding to 100°C.

Class (American Standard) System:

Except for 150Lb (based on 260°C), all other classes are based on 454°C.

Example of Temperature Impact on Pressure

When converting Class 300 simply by pressure, it should be 2.1MPa. However, considering the operating temperature (based on 454°C for Class 300), its corresponding pressure increases. According to material temperature pressure resistance tests, it is equivalent to 5.0MPa. The general corresponding relationship between the two is shown in the table below

Table 1: Conversion Table of Class, "K" Class and Nominal Pressure
Class	150	300	400	600	800	900	1500	2500	2500
K Class	10	20	30	40	-----	63	100	-----	-----
Nominal Pressure PN (MPa)	2.0	5.0	6.8	10.0	-----	15.0	25.0	42.0	42.0

Note: Since nominal pressure and Class have different temperature baselines, there is no strict one-to-one correspondence between them. Table 1 only shows the correspondence for most reference purposes.

3. Common Pressure Standards and Their Corresponding Pressure Values

3.1 DIN Series (National Standard Nominal Pressure)

Nominal Pressure (PN) Corresponding Pressure (MPa)

Nominal Pressure (PN)	Corresponding Pressure (Mpa)
PN 2.5	0.25Mpa
PN 6	0.6Mpa
PN 10	1.0Mpa
PN 16	1.6Mpa
PN 25	2.5Mpa
PN 40	4.0Mpa
PN 63	6.3Mpa
PN 100	10.0Mpa

3.2 ANSI Series

Nominal Pressure (PN) Corresponding Pressure (MPa)

Nominal Pressure (PN)	Corresponding Pressure （Mpa）
PN20	2.0Mpa
PN50	5.0Mpa
PN110	11.0Mpa
PN150	15.0Mpa
PN260	26.0Mpa
PN420	42.0Mpa

3.3 American Standard Series (Class)

Class	Corresponding Pressure (MPa)	Class/60 Calculation Result
Class 150	2.0	150/60 = 2.5
Class 300	5.0	300/60 = 5.0
Class 400	6.3	400/60 ≈ 6.8
Class 600	10.0	600/60 = 10.0
Class 900	15.0	900/60 = 15.0
Class 1500	25.0	1500/60 = 25.0
Class 2500	42.0	-

3.4 Approximate Correlation Table of Pound Class (Class), K-Class, and Nominal Pressure (PN)

Pound Class (Class)	K-Class	Nominal Pressure (PN, MPa)
Class 150	10	2.0
Class 300	20	5.0
Class 400	30	6.8
Class 600	40	10.0
Class 800	63	-
Class 900	100	15.0
Class 1500	-	25.0
Class 2500	-	42.0

Note: Due to different temperature baselines between nominal pressure and pound class, there is no strict one-to-one correspondence. The above table is for approximate reference only.

4.Pressure Unit Conversion and Regional Application Habits

4.1 Common Pressure Units and Conversion Relationships

Unit Definition Conversion Relationship

Unit	Definition	Conversion Relationship
kgf/cm² (kilogram-force per square centimeter)	1 kilogram-force acting on 1 square centimeter (commonly called "kilogram pressure" in China)	1 kgf/cm² ≈ 98.07 kPa ≈ 0.9807 bar ≈ 14.223 psi; 1 MPa ≈ 10.1972 kgf/cm²
psi (pound-force per square inch)	1 pound-force acting on 1 square inch (abbreviation of Pounds per square inch)	1 psi ≈ 6894.76 Pa ≈ 0.00689 MPa; 1 MPa ≈ 145.038 psi
bar (bar)	A non-SI engineering unit based on the metric system	1 bar = 100,000 Pa = 0.1 MPa; 1 bar ≈ 14.5 psi
Pa (Pascal)	Basic SI pressure unit (1 Pa = 1 N/m²)	1 MPa = 1,000,000 Pa = 1000 kPa
atm (standard atmosphere)	Scientific pressure unit (based on 760 mmHg at 0°C)	1 atm = 760 mmHg = 101325 Pa ≈ 0.1013 MPa
torr (torr)	1/760 of 1 standard atmosphere	1 torr = 1 mmHg = 133.3224 Pa
mmHzO (millimeter of water column)	Pressure from 1mm water column at 4°C	1 mmH₂O = 9.80665 Pa
mmHg (millimeter of mercury)	Pressure from 1mm mercury column at 0°C	1 mmHg = 133.322 Pa

4.2 Regional Application Habits

China and Asia: Prefer using "kg" (corresponding to kgf/cm²) for gas pressure description; commonly use MPa in engineering.

Europe: Widely use bar and MPa.

United States and English-speaking countries: prefer using psi (or Class/pound class) for pressure representation.

Coriolis Mass Flowmeter: Key Features & Installation Guidelines

Turbine Flowmeters Inaccurate? Don't Throw Them Away! Master These 5 Key Points First!

Exhibition Information

Product Application

Factory Facilities & Production Capabilities

Product Maintenance and Selection

Technical Documentation: Pressure Standards for Piping, Valves, and Instrumentation