Inspection and Quality Analysis of Valves in Large Petrochemical Devices (Part One)

Abstract: The inspection and pressure test standards of common valves  at home and abroad are compared; pressure test procedures and precautions for valves are introduced in this article. Taking large-scale valve inspections in the petrochemical industry as an example, appearance inspections and pressure tests are carried out; the statistical analysis is performed for the defects found in the inspection, reflecting the quality of Chinese valves to a certain extent and providing data reference for the valve industry.
 
1. Introduction
As indispensable fluid control equipment in petroleum, chemical, natural gas, electric power, metallurgy, water conservancy, and other industries, valves play a vital role in promoting people's life and ensuring industrial production safety. With the rapid development of China's modern industry, matching valves for major petrochemical engineering projects have become the new market development direction of the valve industry. At present, Fujian Province has formed a petrochemical industry cluster focusing on the development of Gulei Petrochemical Base, Meizhou Bay Petrochemical Base and Jiangyin New Chemical Materials Zone. The volume of petrochemical projects is continuously expanding, and the demand for valves is very great. However, there is a difference in the manufacturing of different valve suppliers, and the quality of valves is different. Valves with potential safety hazards can be used less in the project site by carrying out the necessary inspection and pressure test before valve installation.
 
In recent years, many Chinese experts and scholars have conducted in-depth discussions on pressure test standards and inspection quality issues of valves, which have very important guiding significance for personnel on engineering sites. The difference between the nominal pressure and the maximum allowable working pressure at room temperature in the valve pressure test standards at home and abroad is discussed. Choose more reasonable valve pressure test standards to inspect valves from the aspects of valve test medium, pressure test ratio, test pressure, and pressure holding time. Corresponding quality control measures are put forward from the personnel, standards, equipment and methods involved in the pressure test. The deficiencies in the valve's quality inspection are analyzed, and proposed scientific and reasonable quality inspection methods and countermeasures for valves.
 
Combining engineering practice, the application of inspection standards for valves is discussed, and pressure test standards for valves at home and abroad are compared and analyzed; relevant precautions for the pressure test process is proposed and take all newly added valves which are replaced in a large-scale petrochemical enterprise during a major shutdown and overhaul as the research object. Conduct 100% appearance inspection and pressure test of the full batch of valves and perform statistics and analysis for the inspection results to provide a reference for valve related workers.
 
2. Inspection standards and technical requirements of valves 
2.1 Visual inspection of valves
Under normal circumstances, the corresponding quality certification documents are required after the valve arrives, and the product specification is required for special valves. After the valve arrives, a visual inspection is generally required. The visual inspection of the valve mainly includes inspections of signs and nameplates, factory protection, defects of bodies and parts.
 
The signs and nameplates inspection for valves are mainly based on the GB/T12220-2015 and other related standards, but many valve manufacturers fail to strictly implement the standard requirements. The labeling information is not complete. Investigate a large number of newly delivered valves in China; the general valve housing should be marked with the nominal size, nominal pressure, trademark, material number, furnace batch number, medium flow direction, etc., and there should be a sign of no grease on oxygen valves. As for valves with small diameters,  copper alloy valves or aluminum alloy valves that are difficult to be marked, some of the information on the valve body may not be marked, but it must be shown on the nameplates. The opening and closing direction must be marked on the hand wheel or handle, and the opening and closing state should also be marked on the worm wheel. In addition to repeating the main information on the valve body, the nameplate should at least indicate the model specification, maximum operating temperature, maximum allowable working pressure, product number, standard, manufacturing year and month. Relevant labeling information should be added for other special valves such as pressure regulating valves, power station valves, cryogenic valves, safety valves, traps, etc., according to the requirements of the corresponding products. Both the body and nameplate, the information marked should be correct, complete, clear and easy to identify.
 
Factory protection inspection for valves is mainly based on JB/T 106-2004, JB/T 7928-2014 and other relevant standards. The outer surface of cast iron, carbon steel and alloy steel should be uniformly coated with durable and non-toxic protective coatings. The inner cavity of carbon steel and alloy steel valves should also be treated with anti-corrosion or anti-rust treatment. The sealing surface of the valve should be protected from damage. The gate valve and globe valve should be fully closed; the ball valve and plug valve should be fully opened, and the butterfly valve should be slightly opened by 4° to 5°. There should be anti-collision protection for valve clacks and seats of swing check valves, and all connecting ends of valves should be equipped with protective covers that are easily removed; the exposed valve stem should also be covered with protective oil paper.
 
Defect inspections of the valve's housings and parts are mainly based on JB/T7927-2014, SY/T 4102-2013, SH 3518-2013 and other relevant standards. Judging from the macroscopic eyes, there should not be missing parts, peeling of paint, mechanical damage, corrosion and rust for valves. The inner cavity of the valve should be clean and free of foreign matter; the sealing surface must not be damaged, and the nameplate must not fall off. The opening and closing of the valve are flexible and there is no jamming. When the lifting type valve such as gate valves and globe valves are closed, the sealing surface of the valve disc and valve seat should be tightly close to each other and uniformly pressed. When the rotating type of valves such as ball valves and plug valves is opened, the through hole of the opening and closing part and the flow channel should be coaxial. Either the valve body or the part, the surface of castings should be smooth and free of defects such as cracks, shrinkage cavity, sand holes, gas holes, burrs, etc. The surface of the forging should be free of defects such as cracks, scars, short of materials, etc.