Valve Stem Material
Dec 21, 2017
Valve stem is an important accessory in a valve and is used for valve switch or adjustment. It’s not only just a moving part or stress carrying part but also a sealing element when valve opens or shuts. Meanwhile, it will be impacted and corroded by the medium, and rubs with the packing. So when choose valve stem material we should consider the following tips.
1. If it has enough strength under particular temperature?
2. If it has good impact toughness?
3. If it has good anti-rub property?
4. If it has good corrosion resistance?
Because valve stem is a vulnerable part, it’s better to pay more attention to the material machining and heat treatment properties.
Aluminium bronze (QA19-2) and Lead brass(HPB59-1) are generally used for the pressure less than 1.6MPa and temperature less than 200℃.
A5 and 35# steel after Nitrogen treatment are suitable for the valve with pressure less than 2.5MPa. A5 is used for the working temperature less than 300℃ while 35# steel is used for the working temperature less than 450℃.
But in practical application, valve stem in carbon steel is not good at corrosion protection.
Structural Alloy Steel:
38XMIOA, 40X and 20CrMo1V1A steel are common used. 40X steel after chromeplate treatment is suitable for the valve with pressure less than 32MPa and temperature less than 450℃.
38XMIOA steel after Nitrogen treatment is suitable for the valve in power station with pressure bigger than 10MPa and temperature less than 540℃.
20CrMo1V1A steel after Nitrogen treatment is suitable for the valve in power station with pressure bigger than 14MPa and temperature less than 570℃.
SS410 and SS420 are suitable for the water, steam and weak erosive medium with temperature less than 450℃ and nominal pressure less than 32MPa. The surface of this two kinds material can be intensified by chromeplate treatment and high-frequency quenching.
SS431 is suitable for low temperature valve and corrosive medium.
SS304 and SS316 are suitable for the valve with pressure less than 6.4MPa and high temperature valve with temperature less than 600℃ or low temperature stainless steel valve with temperature less than -100℃. SS304 can have the resistance to corrosion medium like nitric acid. While SS316 is more perfect in resistance with corrosion medium like acetic acid.