Plug Valve Selection for New Pipelines: 4 Core Questions to Answer Before Procurement

In the new pipeline projects, the plug valve as crucial cutting-off or regulating equipment, its selection directly affects the long-term reliability, safety and economy of the system. However, many purchasing personnel, when confronted complex technical specification, tend to fall into trap of "overloading with parameters", thereby neglect the core decision-making logic. 70% of pipeline valve failures are caused by incorrect selection rather than product quality issues.Senior engineers emphasize that the following 4 questions must be accurately answered before procurement to avoid hidden dangers from the source.



Question 1: What are the medium characteristics?

The medium is the core basis for plug valve selection. Its physical and chemical properties direct determine the valve structure design.

Clean fluids (such as pure water, natural gas): Ordinary straight-through plug valves can be selected to pursue the advantages of low flow resistance and rapid opening and closing.

Particulate-containing media (such as mud, ore slurry): It is necessary to preferentially choose lubricated plug valves (which inject sealing grease to reduce wear) or eccentric plug valves (which prevent particle blockages in the valve chamber). In a certain mining pipeline project, due to the incorrect use of ordinary plug valves, the valve got stuck and caused the machine to stop running five times within three months.

Easily crystallizable/high-viscosity media (such as resin, asphalt): It is necessary to select a design with a blow-off interface. Regularly clean the crystalline substances on the plug valve seat to prevent the valve from getting stuck.

Special media (such as high corrosive, easily polymerizable fluids): It is necessary to additionally to confirm the compatibility of the valve body material (such as Hastelloy or Monel alloys), and assess the risk of medium aggregation. If necessary, select valve plate with anti-scaling coatings.



Question 2: What is the temperature range?

The operating temperature directly affects the service life of the sealing material and may even lead to safety incidents. Therefore, it is necessary to clearly define the minimum and maximum operating temperatures at the same time.

Normal temperature condition (-20℃ to 150℃): Ordinary PTFE (polytetrafluoroethylene) sealing is sufficient to meet the requirements, and it offers the highest cost-effectiveness.

High temperature conditions (>200℃): The sealing material must be upgraded - PEEK (polyetheretherketone) can be selected for temperatures ranging from 200℃ to 350℃, while for temperatures above 350℃, graphite sealing or metal-to-metal sealing is required. A petrochemical pipeline once experienced leakage due to the use of PTFE sealing at high temperatures, causing the sealing parts to melt.

Low temperature conditions (<-40℃): It is necessary to select special materials with low-temperature impact toughness (such as low-temperature carbon steel, stainless steel), and the sealing components need to be suitable for low-temperature environments (such as modified PTFE) to prevent failure of the seal due to low-temperature cracking.

Temperature fluctuation condition: It is so necessary to take into account the coefficient of thermal expansion and contraction of the materials, and select a plug valve with an elastic compensation design to prevent leakage after temperature cycling.



Question 3: What is the operation frequency?

The working frequency directly determines the sealing form and driving method of the valve. Choosing the wrong one could cause the valve to break down very soon. 

Low-frequency usage (≤ 1 time per day): For example, a maintenance cut-off valve that is only switched on once every few months in a factory. In this case, a soft-sealing plug valve is recommended. Its initial leakage rate is very low (able to meet ANSI 6-level standards), and it is also more cost-effective. 

High-frequency usage (more than 10 times per day): For example, a flow control valve that needs to be adjusted several times a day, or process valves that are frequently switched. Soft seals are prone to being worn out, so it is best to choose metal seals or plug valves with wear-resistant coatings (such as hardfacing stainless steel alloy). Note that the design life test of these valves must reach more than 100,000 times (equivalent to a 10-year lifespan). 

For example: The circulating water switching valve in a certain chemical plant operates 20 times every day. At first, a soft-sealing valve was chosen due to its lower cost. However, within less than half a year, it began to leak internally. Later, a metal-sealing plug valve was replaced, and it has worked fine for three years without any problems. 

How should the driving method be configured? 

High-frequency operation condition: It is recommended to use pneumatic actuators (with fast response, good wear resistance, and not prone to frequent actions), and be equipped with a position feedback device. 
Low frequency and without air source: Just operate manually directly. It's simple and reliable. 

For remote control (such as switching from the central control room): Choose an electric actuator. Remember to specify the protection level (such as IP67, dust and water resistance) and explosion-proof level (such as Ex d IIB T4).



Question 4: Are the safety requirements clear?

Safety is core of pipeline operation. We need to careful check the following requirement one by one to avoid missing any key compliance provisions:

Explosion-proof requirements: If there is any flammable gas at the site, the actuator must have an explosion-proof certification (such as Ex d IIB T4).

Case: In a paint workshop, due to the use of an electric actuator without an explosion-proof certificate, the motor sparks ignited the solvent vapor. After the incident, it was stipulated that if the medium is flammable, the actuator must be explosion-proof. 

Structural safety: The valve stem must have a blowout prevention design to prevent the valve stem from flying out and injuring people in case of abnormal pressure.

Case: During the maintenance of a natural gas station, the valve stem lacked a blowout prevention structure. At the moment of pressure increase, the valve stem broke off and flew out. Subsequently, this requirement was included in the mandatory terms of the procurement. 

Instrumentation system requirements: Valves used in safety instrumented systems (SIS) must clearly indicate the SIL level (such as SIL 2 or SIL 3), and provide functional safety certifications (such as gas loss closure, power loss closure).

Case: The high liquid level interlock valve of a storage tank was supposed to be SIL. During the procurement process, this was not specified. The purchased valves lacked fault safety functionality. The cost for subsequent renovations increased by three times. 
Environmental protection requirements: If there are strict restrictions on leakage at the site, valves should be selected in accordance with low-leakage standards such as ISO 15848-1.

Case: The solvent valve of a reaction tank in a pharmaceutical factory did not meet the low-leakage requirements, and there was always an unpleasant smell at the valve stem. After replacing it with a valve certified by ISO 15848-1, the problem was solved. 
If you have more question or inquires, please contact ZZJG PLUG VALVE.

Previous: Why Anti-Static Design in Plug Valves for LNG and Fuel Oil Pipeline Safety

Next: Back to list