Pressure vessel fabricators and steam boilers are subjected to rigorous tests to ensure they are in compliance with the American Society of Mechanical Engineers (ASME) Broiler and Pressure Vessel codes, rules and regulations. This is required to obtain an ASME certification.
Based on the requirements and specificity of the ASME certification, there are specific ASME codes ascribed to units and production companies based on the specific standards met. These codes, however, do not signify only the size of the unit but also the specific compliance with the ASME BPVC (Boiler Pressure Vessel Code) specifics.
Based on ASME's Section 8, Division 1, there are distinct designations for pressure vessel which indicate that larger vessels should receive the U stamp while smaller or miniature vessels receive the UM stamp.
The main difference between the ASME U-stamp vessel and the UM-stamp vessel manufacturing companies, however, goes beyond the size, even if a person could correctly differentiate primarily between the stamps and vessels using size as a factor.
Other differences between the ASME U-stamp and the UM-stamp vessel manufacturing companies include the inspection procedure undergone by the two stamp vessels respectively. According to the procedure lined up by the certification board, the UM stamp vessels are not required to undergo the same level of inspection as the larger U vessels are subjected to.
Based on this, the UM-stamp vessel manufacturing companies are subjected to lesser scrutiny by the American Society of Mechanical Engineers compared to the U-stamp vessel manufacturing companies. Also, the UM-stamp vessel is not required to have a 3rd party ASME inspector review and approval calculations as required of U-stamp vessels.
To further ensure quality and safety, the U-stamp vessels manufacturing companies are required to have an additional 3rd party hydro test inspector review while this level of inspection is not necessary and required of the UM-stamp vessel manufacturing companies.
Companies with the ASME UM-stamp vessels (which indicates smaller volumes) compared to the U-stamp vessel manufacturing companies undergo an annual audit which is done to check compliance of the companies and vessels with the rules and regulations of the certification board. Meanwhile, the ASME U-stamp vessels manufacturing companies are subjected to inspection once every three years.
The UM stamped pressure vessels are distributed into several categories including:
- Vessel 5 Cubic Foot of volume or smaller with pressure not exceeding 250psi.
- Vessel 3 Cubic Foot of volume or smaller with pressure not exceeding 350psi.
- Vessel 1.5 Cubic Foot of volume or smaller with pressure not exceeding 600psi.
The ASME code which was established to ensure that the fabrication, design and operation of vessels is highly safe and reliable makes it possible for the vessels to operate in a variety of environments and under diverse processes.