THE REMOVABLE AND REPLACEABLE VALVE INTERNAL PARTS that come in contact with the flow medium are collectively termed as VALVE TRIM. These parts include valve seat(s), disc, glands, spacers, guides, bushings, and internal springs. The valve body, bonnet, packing, et cetera that also come in contact with the flow medium are not considered valve trim.
A Valve's trim performance is determined by the disk and seat interface and the relation of the disk position to the seat. Because of the trim, basic motions and flow control are possible. In rotational motion trim designs, the disk slides closely past the seat to produce a change in flow opening. In linear motion trim designs, the disk lifts perpendicularly away from the seat so that an annular orifice appears.
Valve trim parts may be constructed of assorted materials because of the different properties needed to withstand different forces and conditions. Bushings and packing glands do not experience the same forces and conditions as do the valve disc and seat(s).
Flow-medium properties, chemical composition, pressure, temperature, flow rate, velocity and viscosity are some of the important considerations in selecting suitable trim materials. Trim materials may or may not be the same material as the valve body or bonnet.
API has standardized trim materials by assigning a unique number to each set of trim materials.
The Service of Trim
API Trim No.1
For oil and oil vapors and general services with heat treated seats and wedges. General very low erosive or non-corrosive service between -100°C and 320°C. This stainless steel material lends itself readily to hardening by heat treatment and is excellent for contacting parts such as stems, gates, and discs. Steam, gas and general service to 370°C. Oil and Oil vapor 480°C.
API Trim No.2
For moderate pressure in corrosive, low erosive service between -265°C and 450°C.
API Trim No.3
For moderate pressure in corrosive or non corrosive service between -265°C and 450°C.
API Trim No.4
Seats 275 BHN min. As trim 1 but for medium pressure and more corrosive service.
API Trim No.5
High pressure slightly erosive and corrosive service between -265°C and 650°C and higher pressure. Premium trim service to 650°C. Excellent for high pressure water and steam service.
API Trim No.5A
As trim 5 where Co is not allowed.
API Trim No.6
As trim 1 and more corrosive service.
API Trim No.7
Seats 750 BHN min. As trim 1 but for higher pressure and more corrosive/erosive service.
API Trim No.8
Universal trim for general service requiring long service life up to 593°C. As trim 5 for moderate pressure and more corrosive service. Steam, gas and general service to 540°C. Standard trim for gate valves.
API Trim No.8A
As trim 5A for moderate pressure and more corrosive service.
API Trim No.9
For corrosive service to 450°C such as acids, alkalies, salt solutions, etc. Very corrosive fluids.
Erosive-corrosive service between -240°C and 480°C. Resistant to sea water, acids, alkalies. Has excellent corrosion resistance in chlorine and alkylation service.
API Trim No.10
For superior resistance to corrosion for liquids and gases which are corrosive to 410 stainless steel up to 455°C. As trim 2 but a higher level of corrosive service. Provides excellent resistance to corrosive media at high temperatures and toughness for service at low temperatures. Low temperature service standard for 316SS valves.
API Trim No.11
As trim 9 but for medium pressure and more corrosive service.
API Trim No.11A
As trim 9 but for medium pressure and more corrosive service.
API Trim No.12
As trim 10 but for medium pressure and more corrosive service.
API Trim No.12A
As trim 10 but for medium pressure and more corrosive service.
API Trim No.13
Very corrosive service. For moderate pressure between -45°C and 320°C.
API Trim No.14
As trim 13 but for medium pressure and more corrosive service.
API Trim No.14A
As trim 13 but for medium pressure and more corrosive service.
API Trim No.15
As trim 2 but more erosive service and higher pressure.
API Trim No.16
As trim 10 but more erosive service and higher pressure.
API Trim No.17
As trim 13 but more corrosive service and higher pressure. Combines good corrosion resistance with high temperature resistance up to 800°C.
API Trim No.18
As trim 13 but more corrosive service and higher pressure. Water, gas or low pressure steam to 230°C.
API Trim No.Special
Water, oil, gas, or low pressure steam to 232°C.
API Trim No.NACE
Specially treated 316 or 410 trim combined with B7M bolts and 2HM nuts to meet NACE MR-01-75 requirements.
API Trim Full Stellite
Full Hardfaced trim, suitable for abrasive and severe services up to 1200°F (650°C).
