Forged Steel Gate Valve

The gate is a wedge that travels vertically on the bore centreline. Fully open, it stands clear of the flow path so the passage is straight through, with nothing left in the stream to erode, to collect debris or to add resistance. Fully closed, the wedge is driven down between two seat rings and the line pressure finishes the job, pressing the downstream face onto the downstream seat. One straight bore serves both positions, which is why the design holds the lowest pressure drop of any isolation valve; and the wedge has only those two positions, which is why it cannot regulate flow.

The forged vs cast gate valve choice is about defect population, not strength. A casting can hold gas porosity or shrinkage voids that radiography is not certain to find in a body this small, because there is little section to shoot through and the geometry is awkward to place against the film. A forging from billet is directionally worked, with a uniform grain structure and no internal cavity to find at all. The wall also finishes thick relative to the bore, because the body is machined out of solid bar rather than cored. That is the entire commercial case for paying the forging premium below DN 100: not stronger steel per unit section, but a much lower probability that an undetected flaw is sitting in the pressure boundary.

OS&Y, outside screw and yoke, is the stem arrangement named in almost every datasheet, and it is specified for maintenance rather than convention. The operating thread sits above the gland and outside the pressure boundary, while the stem section passing through the packing stays smooth and unthreaded, so the packing seals against a plain surface instead of a thread. The stem translates without rotating, which makes the exposed length an unambiguous position indicator - nobody has to guess whether the gate is shut - and lets the thread be greased in place with the valve still in service. The ISRS (inside screw rising stem) alternative buries the thread inside the bonnet, in contact with the medium, which is the arrangement a dirty or corrosive line punishes first. That is why API 602 restricts ISRS to NPS 2½ (DN 65) and Class 800, while allowing OS&Y across the full NPS ¼ to 4 range.

Flow direction is unrestricted. A gate valve is bidirectional and the body carries no direction arrow to respect, because either face seals equally well; a globe valve is a directional valve and has to be installed the right way round. The limitation runs the other way. This valve cannot throttle, and any duty between fully open and fully closed belongs to a forged steel globe valve.

Design Standard

Design Features

1. Low fluid resistance and erosion resistance.
2. Compact structure can be applied in many industries.
3. Easy for maintenance.
4. Optional pressure seal design.
5. Optional bellows seal.

Lug Type Dual Plate Check Valve drawing

Material Specification

Dimension & Weight

Class 800

Class 900

Class 1500

Class 2500

valve factory

 

 

 

 

GNEE is a forged steel gate valve manufacturer with in-house forging, machining and assembly, and a forged steel gate valve supplier to more than 180 countries and regions. Every order includes individual API 598 pressure testing with a report per serial number, EN 10204 3.1 material certificates traceable to heat number, end protectors and a sealed plywood case, and a 24-hour technical response on specification questions. Third-party inspection is scheduled against the production date so the witness sees the test rather than the packing.

For a China forged steel gate valve quotation, send the seven items below. Anything left out becomes an assumption, and the two assumptions that cause rework are the bore code and the end connection.

1. Size and pressure class - NPS or DN, and Class 150 / 300 / 600 / 800 / 1500, or Class 2500 if you accept ISO 15761 certification.
2. Body material - A105, A350 LF2, or the A182 alloy or stainless grade, with the design temperature that drives it.
3. Trim number - 8 unless the duty says otherwise.
4. End connection and bore - socket weld, NPT, butt weld or flanged; reduced bore or full bore, and the pipe schedule being welded to.
5. Bonnet type - bolted, welded or pressure seal; and the stem arrangement if not OS&Y.
6. Operation - handwheel, worm gear operator, or actuator with the supply and control details.
7. Supplementary requirements - NACE MR0175, ISO 15848-1 packing, certificate level, third-party inspection body, and destination port.

Send that list and our technical team will confirm the specification against API 602 scope and return a quotation with lead time within 24 hours. Contact GNEE.

FAQ

What does Class 800 mean on a forged gate valve?

Class 800 is not a listed class in ASME B16.34. It is an intermediate rating defined by interpolation between the two classes that bracket it: P800 = one third of the Class 600 rating plus two thirds of the Class 900 rating, read at the same design temperature and within the same material group, then rounded to the nearest 10 kPa (0.1 bar). For an A105 body between −29 and 38 °C that gives about 136 bar, or 1,975 psi. Class 800 sits two thirds of the way from 600 to 900, which is why it is much closer to 900 than the number suggests.

Is Class 800 the same as PN160?

No. PN160 is 16.0 MPa. Class 800 for A105 works out to about 13.6 MPa, and Class 900 is 15.3 MPa, so a PN160 body is actually rated above Class 900 and well above Class 800. The trailing number on a Chinese model code is the nominal pressure in MPa multiplied by ten, not a pound class, and the two systems do not convert one to one.

What is the maximum temperature of a forged steel gate valve?

The ceiling belongs to the body material, not to the valve type. ASTM A105 covers −29 to 425 °C and is permitted but not recommended for prolonged service above that. A350 LF2 stops at 343 °C, A182 F11 and F22 reach 593 °C, and A182 F304 and F316 are rated from −196 to 538 °C. Above about 540 °C the allowable pressure falls to a fraction of the ambient rating, so the class number alone tells you nothing about what the valve will hold.

Should I specify a bolted bonnet or a welded bonnet?

A bolted bonnet with a spiral wound stainless gasket is the default because it can be opened on site for inspection and trim replacement. A welded bonnet deletes the body-bonnet gasket, which is the one joint that can leak to atmosphere, and is chosen where the valve will not be repaired in place and where the release of process fluid is the dominant risk. A pressure seal bonnet uses line pressure to tighten its own seal and belongs to cast bodies at Class 900 and above rather than to compact forgings.

Can a gate valve be used for throttling?

No. A gate valve has two service positions, fully open and fully closed. Part of the way open, the gap between the lower edge of the gate and the seat is a narrow irregular orifice, and local velocity there can climb from a design figure of 3 to 5 m/s to above 20 m/s. The result is vortex-induced vibration of the gate, erosion and wire drawing of both seating faces, and loosening of the stem and packing. Gate valve throttling is the single most common specification shortcut that ends in an unplanned shutdown; use a globe valve instead.

What seat leakage rate applies to a metal-seated forged gate valve?

API 598 sets the test and gives a size-dependent allowance in drops per minute on the high-pressure closure test. At NPS 2 and below that allowance is zero, even with a metal seat, so the common claim that a metal-seated small valve must be allowed to weep does not hold. Above NPS 2 the allowance rises with size and the tabulated values differ between editions, so name the edition on the purchase order. Where a project quotes ISO 5208 instead, Rate D is the metal-seated fallback and Rate A means no visible leakage, but ISO 5208 and API 598 leakage figures are different units and cannot be substituted for each other.

What is the difference between API 602 and API 600?

API 602 covers compact forged steel gate, globe and check valves up to DN 100 (NPS 4) in Classes 150 to 1500. API 600 covers cast bolted-bonnet gate valves from NPS 2 upward in Classes 150 to 2500. Between NPS 2 and NPS 4 both are available, and the usual dividing line in a project piping specification is the end connection. Socket weld and threaded ends point to the forged valve; flanged ends point to the cast valve. API 602 valves are not simply smaller versions of API 600 valves: they carry a heavier wall and their own stem dimensions.

Can you supply a Class 2500 forged steel gate valve?

Yes, but not as an API 602 valve. The API 602 pressure class list ends at Class 1500. Class 2500 forged valves are built and certified to ISO 15761:2020, which added Class 2500 together with PN 63, 250 and 400 in its 2020 revision, or to ASME B16.34 with a purchaser specification. Write that standard on the order, because a certificate naming API 602 for a Class 2500 valve cannot be defended.

Which trim should I specify on a carbon steel body?

Trim 8 is the default: a 13Cr disc and stem with cobalt-based hardfacing on the seat ring. It covers steam, water, oil and gas at moderate velocity for a small premium over all-13Cr trim. Move to trim 5, hardfacing on both disc and seat, when the duty is erosive or the valve cycles often. Move to trim 10, 12 or 16 when the body is stainless and the medium is corrosive. State the trim number rather than the material names, because the number is what the shop floor reads.

Can forged steel gate valves be used in sour service?

Yes, to NACE MR0175 / ISO 15156, and it has to be written into the order before manufacture. The requirement caps hardness at 22 HRC, which A105 meets at 187 HBW maximum only after normalising or normalising and tempering. A valve made without that discipline cannot be certified into it afterwards, because the hardness and heat treatment records cannot be created retroactively.

What end connection should I specify?

Socket weld to ASME B16.11 for small bore high pressure, NPT to ASME B1.20.1 where the valve may be removed, and butt weld to ASME B16.25 for the highest integrity joints. The decision buyers most often get wrong is the bore class rather than the end type: the valve bore has to be sized to match the fitting class of the pipe it welds to, and a mismatch shows up on site as a step at the weld root or a socket that will not take the pipe.

What is the minimum order quantity and lead time?

One piece. Standard sizes in A105 with trim 8 ship from stock in about 7 days. Alloy and stainless bodies, non-standard trims, tapped or special end configurations and NACE orders run 20 to 25 days from drawing approval. Freight from Tianjin to most destinations adds 18 to 35 days depending on the port and the service.

What certificates come with each valve?

EN 10204 3.1 material certificates for body, bonnet, stem and disc, traceable to heat number, plus an API 598 test report recording shell, seat and backseat pressures with the result per valve. A dimensional report and a hydrotest record for each serial number are issued on request. EN 10204 3.2 adds independent witnessing and is arranged with SGS, TÜV, Bureau Veritas, Lloyd's Register or Intertek, scheduled against the production date rather than after packing.

Do you offer OEM and ODM, and what warranty applies?

Both. OEM means your nameplate, your tag numbering and your documentation format on our standard patterns; ODM means building to your drawing where face-to-face length, bore or end configuration differ from our catalogue. The 18-month warranty from shipment covers manufacturing defects. Wear parts are available for the service life of the valve: gate, stem, seat rings, packing, body-bonnet gasket and gland bolts.