Does a pressure pipeline cease to be considered a pressure pipeline if its diameter is less than DN40? What other people have told me

There is no such thing; it has nothing to do with the pipe diameter

Yes, pressure pipeline monitoring is only conducted on pipelines with a value of 40 or higher

The \"Regulations on the Safety Supervision of Special Equipment\" (State Council Order No. 549), issued and implemented by the State Council on May 1, 2009, further defines pressure pipelines as \"tubular devices that use a certain pressure to transport gases or liquids. Such pipelines include those in which the maximum operating pressure is greater than or equal to 0.1 MPa (gauge pressure), and which are used to transport gas, liquefied gas, steam, or liquid media that are flammable, explosive, toxic, corrosive, or have a maximum operating temperature greater than or equal to their standard boiling point; furthermore, these pipelines must have a nominal diameter of more than 25 mm.\" In other words, the so-called \"pressure pipeline\" refers not only to one that is subjected to pressure inside or outside its pipes, but also to one in which the medium transported within it is \"gases, liquefied gases, and steam\" or \"liquids that may cause combustion, explosion, poisoning, or corrosion\". The \"Regulations on the Safety Supervision of Special Equipment\" issued by the State Council clearly stipulate that pressure pipelines, boilers, pressure vessels, and lifting machinery are classified as special equipment with numerous safety hazards. **In the list of 8,000 items in the Special Equipment Catalogue attached to the Announcement by the General Administration of Quality Supervision, Inspection and Quarantine issued on October 30, 2014, titled \"Announcement by the General Administration of Quality Supervision, Inspection and Quarantine on the Revision of the Special Equipment Catalogue (No. 114, 2014)\\", this definition has been changed as follows: A pressure pipeline refers to a tubular device that uses a certain pressure to transport gases or liquids. It is defined as a pipeline with a maximum operating pressure of 0.1 MPa (gauge pressure) or more, carrying gases, liquefied gases, steam, or liquids that are flammable, explosive, toxic, corrosive, and have a maximum operating temperature equal to or higher than their standard boiling point, and with a nominal diameter of 50 mm or more. Except for pipes with a nominal diameter of less than 150 mm and a maximum operating pressure of less than 1.6 MPa (gauge pressure), as well as the pipes that form part of the equipment used for transporting non-toxic, non-flammable, and non-corrosive gases.

For a reply like #4, what else can I do besides just responding back?:)

I would like to ask the experts: what qualifications or documents are required for the design, construction, and registration of pressure pipelines?

The design requires qualifications for pressure pipeline design. Construction requires qualifications for pressure pipeline work, especially welding. The requirements for submitting documents vary from place to place; just ask the local quality supervision bureau.

Even for just one 1-meter pressure pipeline, is a design qualification required? Is a construction qualification needed, and does it have to be reported as well?

All pressure pipelines subject to regulation must have design qualifications and construction qualifications.

You need to determine whether it is a pressure pipeline or a pressure pipeline that falls under the category of special equipment; special equipment is subject to supervision by the quality supervision agency and also requires testing. When we talk about pressure pipelines in everyday conversation, we are referring to those that fall under the category of special equipment; however, this is not always the case. Any pipeline that is subject to pressure can be considered a pressure pipeline, but it does not necessarily belong to the category of special equipment. Pressure pipelines, which fall under the category of special equipment, are defined as tubular devices that use pressure to transport gases or liquids. They are considered to be such pipelines when their maximum operating pressure is 0.1 MPa (gauge pressure) or more, the medium transported is a gas, liquefied gas, steam, or a liquid that is flammable, explosive, toxic, corrosive, and whose maximum operating temperature is equal to or higher than its standard boiling point, and the nominal diameter of these pipelines is 50 mm or more. Except for pipes with a nominal diameter of less than 150 mm and a maximum operating pressure of less than 1.6 MPa (gauge pressure), as well as the pipes that form part of the equipment used for transporting non-toxic, non-flammable, and non-corrosive gases. Among them, the safety supervision and management of oil and gas pipelines shall also be carried out in accordance with laws and regulations such as the Work Safety Law and the Oil and Gas Pipeline Protection Law. Because if a pressure pipeline is considered a special type of equipment, it is subject to the regulations set out in the \"Regulations on the Safety Supervision of Special Equipment,\" and it is necessary to submit relevant documents to the quality supervision agency. Where there is a policy, there is a countermeasure; the documents that need to be submitted vary from one geological supervision bureau to another, and companies should inquire with their local geological supervision bureaus to find out what documents are required.