ASME and Pressure Vessel Design Considerations for Thermal Fluid Systems

Pressure vessels are containers used for holding gases, vapors, or liquids with pressures above or below the ambient pressure. Since the vessels operate under pressure in industrial applications, their fabrication must adhere to a strict code of construction, including the ASME code — also called the ASME Boiler & Pressure Vessel Code or BPVC.

ASME, short for the American Society of Mechanical Engineers, is one of the leading authorities that regulates pressure vessels and boilers. At Sigma Thermal, we uphold exceptional design and quality standards for all of our products, as evidenced by our adherence to ASME requirements.

Types of Pressure Vessels

There are two main types of pressure vessels used in thermal fluid systems:

• Heat Exchangers: Heat exchangers enable heat transfer between fluids while preventing direct contact between them. Popular applications of these systems include energy, food, bioprocessing, and pharmaceutical industries. Most heat exchangers have a series of metal tubes where one product flows through while the other flows around the tubes allowing heat exchange to occur.
• Fluid Heaters: Fluid heaters are closed vessels that facilitate the exchange of heat from an electrical or fuel-based source to the heat transfer fluid. These systems are used to heat liquids directly or indirectly.

At Sigma Thermal, we primarily use carbon and stainless steel to manufacture our pressure vessels. However, we can construct pressure vessels using other materials approved in the ASME Sect. II part D.

Design Considerations

Below are design aspects to consider when building a pressure vessel:

1. Pressure

Calculation of vessel specifications occurs around the design pressure, a value obtained from the maximum operating pressure expected during startups, emergency shutdowns, process abnormalities, and other upset conditions. Design pressure should be 5-10% above the maximum operating pressure. If the vessel has the likelihood of experiencing vacuum pressure, the design pressure must be a value that resists a full vacuum (-14.7 PSIG).

2. Temperature

The maximum allowable pressure depends on the temperature because material strength may be lower with increasing temperature, and material toughness may be lower in low temperatures. Pressure vessels should not operate at a temperature above the evaluated maximum allowable stress value. Therefore, the design temperature is always less than the minimum temperature and greater than the maximum operating temperature.

3. Corrosion allowance

Corrosion allowance requirements may vary by manufacturer or engineering specifier. Heat exchanger equipment specifically requires a small corrosion allowance because wall thickness affects the heat transfer rate.

4. Allowable stress

The maximum allowable stress of a pressure vessel is determined by ASME Section II part D. The stress values in ASME Section II part D account for potential deviations from the ideal construction and operation of the pressure vessel.

5. Joint efficiency

Another thing to consider in pressure vessel design is joint efficiency. Joint efficiency refers to the ratio of the strength of the welded plate to that of the unwelded plate. Joint efficiencies are determined by the ASME BPV Code Sec. VIII D.1.

Design Considerations for Pressure Vessels Related to ASME

Importance of ASME for safety and quality

ASME standards provide guidelines that help prevent accidents by making pressure vessels safer. Therefore, ASME certification is an accreditation that a piece of equipment adheres to the ASME code. Having a pressure vessel with an ASME stamp is an assurance that is proven to comply with the quality and safety standards of the Boiler and Pressure Vessel Code.

Requirements of ASME

ASME codes cover everything, including the design, creation, maintenance, and adjustments of pressurized equipment. Pressure vessels, heat exchangers use ASME code VIII-1, while hot water heaters and boilers use ASME code I. The design by rules codes give formula methods that work if the design falls clearly within the range of the code.

Thermal Fluid Heating Systems From Sigma Thermal

At Sigma Thermal, we have years of experience designing and manufacturing ASME code-compliant thermal fluid heating systems. We are proud to offer our customers with high-quality heating solutions they need to maintain seamless and efficient operations in their plants. Contact us today to learn more or request a quote and our representatives will get in touch with you.