News Center
21
2022
-
03
What are the leakage and maintenance of valve body and bonnet?
A valve is a control component in a pipeline fluid transportation system, used to change the pipeline cross-section and the direction of the medium flow. It has the functions of guiding, cutting off, throttling, check, diverting, or overflow pressure relief. Therefore, valve leakage is our primary concern regarding valve quality. Today, let's introduce the causes of valve body and bonnet leakage in valve components and their maintenance methods.
Valves are control elements in pipeline fluid transportation systems, used to change pipeline cross-sections and medium flow directions. They have functions such as diverting, cutting off, throttling, check, diverting, or overflow pressure relief. Therefore, valve leakage is our primary concern regarding valve quality. Today, let's introduce the causes of valve body and bonnet leakage in valve components and their maintenance methods.
Causes of valve body and bonnet leakage:
(1) The casting quality of cast iron parts is not high, and the valve body and bonnet have defects such as sand holes, loose structure, and slag inclusions;
(2) Cold weather and freeze cracking;
(3) Poor welding, slag inclusions, unwelded areas, stress cracks, and other defects;
(4) Cast iron valves are damaged after being hit by heavy objects.
Recommended maintenance methods for valves:
(1) Improve the quality of castings and strictly conduct strength tests according to regulations before installation;
(2) Valves with an ambient temperature of 0℃ and below should be insulated or heated, and stagnant water should be removed from valves that are out of service;
(3) The valve body and bonnet welds made by welding shall be carried out in accordance with relevant welding operation procedures, and flaw detection and strength tests shall be carried out after welding;
(4) It is forbidden to push, press, and place heavy objects on the valve. It is not allowed to hit cast iron and non-metallic valves with a hammer. Large-diameter valves should be installed with brackets.
The arrow on the valve body is the recommended pressure-bearing direction of the valve, not the flow direction of the pipeline medium. Valves with bidirectional sealing function cannot be marked with an indicating arrow, or an arrow can be marked, because the valve arrow refers to the recommended pressure-bearing direction, one of the left, right, or up and down directions is better.
The arrow direction marked on the valve body indicates the pressure-bearing direction of the valve, which is usually marked as the medium flow direction by engineering installation companies. Incorrect installation can cause leakage and even pipeline accidents.
The pressure-bearing direction refers to the closed state of the valve after it is applied to the pipeline condition. The arrow direction of the valve body is the recommended pressure-bearing direction. If it is not installed properly, there may be a leakage failure where the valve is not tightly closed. Chaoda's soft-sealed ball valves are usually bidirectional sealed, and arrows are usually not marked. Metal hard-sealed ball valves can be bidirectionally sealed, but there is still one direction with better sealing performance. Therefore, arrows will also be marked, which refers to the recommended pressure-bearing direction of the valve.
Technical treatment of fully welded ball valve body:
1: Heat treatment technology
The thick-walled multi-layer welding process is a process of repeated heating and cooling of metal materials, which leads to uneven structure, poor quality, high residual stress, and even welding defects in the welded joint. Welding is a process after product assembly. The valve cavity contains non-metallic sealing materials such as rubber and PTFE plastic, so post-weld heat treatment cannot be performed.
2: Combined treatment
In the design of valve body welded joints, there is an annular assembly gap at the root of the weld for alignment and positioning. Under the action of internal pressure and external load, this gap will generate stress concentration several times higher than the normal working stress, which is also difficult for engineers to deal with.
The stress concentration, residual stress, and poor structure at the root gap of the valve body welded joint have become weak links in the valve body structure, which has attracted the attention of the valve industry at home and abroad, but there are no related reports to solve this problem, which has become a hidden danger to the structural integrity of the product boundary.
Valve body
Shandong Gongchen Machinery Technology Co., Ltd.
Contact QQ: 258506508
Mobile Number:15621618888
Phone:0536-7691368 7691229
Fax: 0536-7691229
Contact Email:guisongzhng8@gmail.com
Website:www.shandonggongchen.com Gongchen.China Valve Castings.China
Address: Mucun Town, Fangzi District, Weifang City, Shandong Province
Public Account