What standard must pressure vessels comply with according to the regulations?

Pressure vessels must comply with the ASME Boiler and Pressure Vessel Code, which establishes the standards for the design, manufacturing, and inspection of pressure vessels. This code ensures safety and reliability in operations involving high-pressure systems, like those used for compressed natural gas.

The ASME standards are critical in dictating requirements that help prevent failures that could result in catastrophic events, ensuring that vessels can withstand the pressures and conditions under which they operate. Compliance with this code is mandatory for manufacturers and operators of pressure vessels, as it enhances safety and operational integrity.

In contrast, the other standards mentioned serve different purposes: ASTM D 638 is related to tensile properties of plastics, ISO 9001 focuses on quality management systems, and NFPA 70E pertains to electrical safety in the workplace. None of these are specifically applicable to the design and safety standards for pressure vessels, which is why they do not fit the question.