Convert Between ASME & ISO Connection Standards

Understanding the differences between ISO and ASME standards in industrial valve design is crucial due to the varying units of measurement and specifications used globally. These standards, developed by the International Organization for Standardization (ISO) and the American Society of Mechanical Engineers (ASME) ensure the safety, reliability, and interoperability of mechanical systems and components. This article explores the fundamental differences and notable similarities between ASME and ISO along with a section discussing how to compare and convert pipe sizes between different standards.

What are ASME and ISO standards?

ASME focuses on mechanical engineering and related fields, providing standards for pressure vessels, piping, and mechanical components. It primarily uses imperial units (inches, pounds), which are common in the United States.

ISO develops international standards across diverse sectors, including technology, manufacturing, and environmental management. It predominantly uses metric units (meters, kilograms), which are widely adopted globally. For most modern engineering and technical applications in the UK, metric units are the standard.

Both ASME and ISO organizations aim to enhance product quality, safety, and interoperability, ensuring consistent practices across different regions.

Converting nominal diameter (DN) values from ISO to ASME measurements

Table 1 helps compare and convert pipe sizes between different standards, making it simpler to ensure compatibility. This is particularly useful when the user encounters a pipe size specified in one standard but their application or reference material uses a different standard.

• DN (Diameter Nominal): Shows the nominal diameter of pipes in millimeters, commonly used in Europe and internationally.
• ISO / mm: Provides the actual outside diameter of pipes in millimeters according to ISO standards.
• G (BSP): Lists the nominal bore sizes in inches for British Standard Pipe (BSP) threads, used for threaded pipe fittings.
• ASME / inches: Gives the nominal pipe sizes in inches according to ASME standards, widely used in the United States.

Table 1: ISO to ASME conversion chart

DN	ISO / mm	G (BSP)	ASME / inches
10	17.2	G 3/8	3/8″
15	21.3	G 1/2	1/2″
20	26.9	G 3/4	3/4″
25	33.7	G 1	1″
32	42.4	G 1 1/4	1 1/4″
40	48.3	G 1 1/2	1 1/2″
50	60.3	G 2	2″
65	76.1	G 2 1/2	2 1/2″
80	88.9	G 3	3″
100	114.3	G 4	4″
125	139.7	G 5	5″
150	168.3	G 6	6″
200	219.1	G 8	8″
250	273	G 10	10″
300	323.9	G 12	12″
350	355.6	G 14	14″
400	406.4	G 16	16″
450	457.2	G 18	18″
500	508	G 20	20″
600	609.6	G 24	24″
700	711.2	G 28	28″
800	812.8	G 32	32″
900	914.4	G 36	36″
1000	1016.8	G 40	40″

Key similarities

• Standards development: Both ASME and ISO follow rigorous processes for developing and updating their standards, involving input from experts, stakeholders, and consensus-based decision-making.
• Global recognition: ASME and ISO standards are internationally recognized and respected, contributing to improved product quality, safety, and competitiveness in the global market.
• Safety and quality: Both organizations prioritize safety, quality, and efficiency in their standards, aiming to enhance processes and reduce risks across various industries.

ASME vs ISO: Differences between ASME and ISO standards

• Scope: ASME primarily focuses on standards and codes related to mechanical engineering, particularly in areas like pressure equipment, power generation, and manufacturing processes. In contrast, ISO develops standards across a wide range of industries, including quality management, environmental management, and information technology.
• Units of measurement: ISO standards use metric units (millimeters), while ASME standards use imperial units (inches).
• Geographic influence: ASME's influence is most significant in the United States, where its codes and standards are widely adopted and regulated. ISO operates on a global scale, with its standards being adopted and implemented in nearly every country, emphasizing international consensus and harmonization.
• Industry focus: ASME standards are tailored for specific industries such as aerospace, petrochemicals, and nuclear power, with a strong emphasis on safety and performance. ISO standards, on the other hand, address a broader array of industries, including manufacturing, healthcare, energy management, and information technology, extending beyond just engineering.