DN400 PN63 Trunnion-Mounted Ball Valve in 09G2S Low-Alloy Steel: Design, Limits And Selection

1. What a DN400 PN 63 trunnion-mounted ball valve is

Trunnion-mounted versus floating

Ball valves divide by the way the ball is supported. In a floating ball design (плавающая пробка) the ball has no trunnion support; line pressure pushes it against the downstream seat to seal. In a trunnion-mounted design (шар в опорах / цапфах) the ball is carried on top and bottom trunnions and stays in position while the seats float against it. GOST 28343-89 clause 8 lists both as standard constructions.

AtDN400 the difference is amplified:

• Operating torque. In a floating design, the friction torque produced by the ball being forced against the seat rises steeply with size. A DN400 valve in that design is very hard to operate by hand and normally needs an actuator. A trunnion design transfers the thrust to the trunnions, so torque grows much more gently with size.

• Sealing and bleed. Trunnion designs commonly use two seats with an independent cavity between them and a bleed path — one reason pipeline service favours this construction.

• Seat replaceability. GOST 28343-89 clause 8.4 requires seat rings or seat assemblies to be replaceable, but explicitly excludes non-split welded bodies. If the valve uses a fully welded body, seat replaceability must not be claimed.

Full bore, reduced bore, and a frequent misreading

GOST 28343-89 clause 4 distinguishes full bore (полный проход) from reduced bore (суженный проход) and refers face-to-face dimensions to ISO 5752.

This is where a frequent misreading occurs: nominal size is not the actual bore. Per GOST 28343-89 Table 3, the effective diameter of a DN400 valve — defined in clause 3.4 as the specified minimum flow-section diameter with the closure fully open — is 305 mm reduced bore, and 380 mm or 375 mm full bore, depending on the Ру value. Per Table 2, the inlet bore d for DN400 is 385 mm or 375 mm, again depending on Ру.

Three consequences need to be stated plainly:

1. Flow capacity is set by the ball bore, not by the flange size. Estimating flow from the flange diameter will overestimate it.

2. Flange size and type, ball diameter and actual bore all have to be checked item by item on the drawing — the DN400 in the model code is not enough.

3. The pressure rating applies to the end connections, not to the ball bore. At the same DN400, reduced and full bore differ substantially in capacity, so the choice must be explicit.

2. What PN 63 actually means

PN is a 20 °C reference value

GOST 9544-2015 clause 3.1.12 defines PN as the maximum gauge pressure, in bar (kgf/cm²), at a working medium temperature of 20 °C, at which the specified service life of the valve body parts is ensured — the value corresponding to dimensions calculated for the selected material and its strength characteristics at 20 °C.

In other words, PN 63 means "the nominal pressure calculated at a 20 °C reference for the material at 20 °C", not "63 bar at any temperature".

The engineering consequence is direct: as temperature rises, allowable material stress falls and the permissible working pressure has to be reduced accordingly; as temperature falls, material toughness becomes an additional consideration. The permissible working pressure at a specific temperature must be taken from the design document, the applicable pressure–temperature rating table, and the nameplate marking.

GOST 28343-89 clause 7 states this explicitly: permissible pressure–temperature relationships for bodies are taken from the corresponding tables of ISO 7005-1, and limits related to seat and seal materials are set by the manufacturer and stated on the nameplate (clause 12.3 requires the nameplate to carry both the maximum permissible temperature and the corresponding pressure). That wording establishes two things at once — the rating has a standards basis, and it may carry additional manufacturer-set limits.

PN and Class cannot be interchanged

This correspondence comes from GOST 9544-2015 Annex A, Table A.2, which is an informative annex, not a mandatory equivalence, and which states that intermediate values should be interpolated. Three cautions apply:

• PN and Class are two independent systems with different reference temperatures and different flange dimension systems. PN flanges are generally drilled to the GOST 33259-2015 / EN 1092-1 series, Class flanges to ASME B16.5. They cannot be bolted together directly.

• There is no "Class 63" in the ASME pressure-class system. Do not invent one.

• PN is a nominal designation, not a working pressure limit.

One useful conversion to note: DN400 corresponds to NPS 16 (GOST 9544-2015 Annex A, Table A.1). Writing "16-inch" in English-language material is correct.

3. Why an 09G2S low-alloy steel body

What the material is

09G2S (09Г2С) is a low-alloy, silicon-manganese structural steel specified in GOST 19281-2014. The designation reads: about 0.09% carbon (actually ≤0.12%), about 2% manganese (actually 1.30–1.70%), and up to 1% silicon (actually 0.50–0.80%).

Several properties determine its use in valves:

• Strength with toughness. GOST 19281-2014 specifies properties by strength class (265, 295, 315, 325, 345, 355, 375), the applicable class depending on thickness and product form. Low-temperature impact toughness is explicitly specified — the standard sets KCU requirements at −70 °C (categories 6 and 15), which is the core reason the grade is used for cold-climate valves.

• Weldability. The low carbon content (≤0.12%) allows conventional welding methods, generally without preheating and without mandatory post-weld heat treatment.

• Lower cost than stainless steel. Where the medium is not corrosive, it is a more economical choice than 304 or 316.

Trade-offs against carbon and stainless steel

One point must be stated: 09G2S is not a corrosion-resistant material. Its advantages lie in mechanical properties and low-temperature toughness. Corrosivity of the medium still has to be assessed separately — alloying elements in the grade do not by themselves imply corrosion resistance.

Do not treat it as interchangeable with S345 / Q345

Equating 09G2S directly with S345 or Q345 is common but requires care: the sulfur limits and other requirements differ between them (for example, the sulfur limit for S345 is tighter than for 09G2S). Substitution should be agreed explicitly in the order; it is not an automatic equivalence.

4. Temperature limits of 09G2S

This is the part that most needs stating precisely — and the part most often written incorrectly.

The usable temperature depends on delivery standard and product category

Under the relevant tables of GOST 33260-2015 (selection of metals for pipeline valves), when 09G2S is used for bodies, bonnets and flanges, the usable temperature is not a single value but varies with the delivery standard and the rolled-product category:

Material temperature is not valve temperature

Even with the body material's usable temperature confirmed, whether the complete valve can be used at that temperature still depends on: bonnet material and construction (an extended bonnet may be needed for buried or low-temperature service), bolting material (for example A320 L7 for low temperature), gasket material, seat and seal materials, face-to-face and end-connection type, and any low-temperature testing specified by the project. If any one of these is unconfirmed, the complete valve cannot be declared suitable for that temperature.

Seat and seal temperatures: relative positioning only

Temperature limits and media compatibility vary widely across seat and seal materials, from PTFE, RPTFE and reinforced PTFE through PEEK to metal-seated designs. These values should not be written as fixed numbers. Use the pointing formulation: "per the seal supplier's data sheet and the project specification".

"Cryogenic" is off limits

Cryogenic normally refers to service far below −46 °C — LNG at roughly −162 °C, liquid nitrogen at roughly −196 °C. 09G2S is a low-temperature low-alloy steel, not a cryogenic material. English pages should use "low-temperature", Chinese pages , and the term "cryogenic ball valve" should be avoided. This is both a technical accuracy issue and a compliance risk under misleading-claim rules.

5. Which standard a PN 63 valve is built to

63 is absent from the GOST 28343-89 nominal-pressure row

GOST 28343-89 (ISO 7121-86), Flanged steel ball valves — Technical requirements, applies to DN 10–500 mm and Ру 1–10 MPa (10–100 kgf/cm²), for new designs. Clause 5 gives the DN series as 10, 15, 20, 25, 32, 40, 50, 65, 80, 100, 150, 200, 250, 300, 350, 400, 450, 500. Clause 6 gives the Ру series as 10, 16, 20, 25, 40, 50, 100 kgf/cm².

63 is not in that series.

Three practical consequences follow:

1. A PN 63 valve falls outside the Ру series of that standard and is normally built to project specifications (ТУ or the project specification), referencing GOST 33259-2015 flanges and API 6D / ISO 14313.

2. The values in Tables 1 (minimum wall thickness), 2 (inlet bore) and 3 (effective diameter) of that standard must not be applied directly to a PN 63 valve. They can serve as an order-of-magnitude reference within the same design system, but the actual wall thickness and bore of a PN 63 valve must come from the manufacturer's drawing and the project specification.

3. Do not interpolate. The standard has no 63 column, so a calculation such as "Ру 40 gives 15.4 mm, so Ру 63 is about 18 mm" has no standards basis and amounts to fabrication.

As an order-of-magnitude reference, minimum body wall thickness for DN400 in Table 1 of that standard is: Ру 10 → 9.6 mm, Ру 16 → 11.0 mm, Ру 20 → 11.2 mm, Ру 25 → 12.7 mm, Ру 40 → 15.4 mm, Ру 50 → 17.5 mm, Ру 100 → 27.7 mm. There is a clear step between Ру 50 and Ру 100 — which is precisely why interpolating to guess Ру 63 is unsafe.

Flanges: GOST 33259-2015

GOST 33259-2015 covers connecting flanges of pipeline valves, fittings and pipelines at nominal pressures up to PN 250, including the design, dimensions, sealing-face types and technical requirements for steel and cast iron flanges. Its PN series is 1, 2.5, 6, 10, 16, 25, 40, 63, 100, 160, 200, 250 kgf/cm², and its DN series runs from DN 10 to DN 4000.

Two cautions:

• PN 63 is in the PN series, but whether a given DN and PN combination is applicable must be checked item by item in the standard's tables. The existence of 63 in the series does not by itself mean a DN400 × PN 63 dimension exists.

• Flange types include 01 (plate, welded-on), 02 (loose, on a welded-on ring), 03 / 04 (lapped / clamped), 11 (butt-welded) and 21 (cast body flange). The standard mentions L and M sealing-face forms for PTFE gaskets.

• GOST 28343-89 clause 8.1.3.2 refers connecting flanges to ISO 7005-1, and clause 8.1.3.3 notes that flanges may be cast or forged integrally with the body, or welded on (butt-welded for DN > 50), followed by the heat treatment needed to allow the material to be used across the full working temperature range.

Pipeline service: API 6D / ISO 14313

For trunk pipeline service, the design basis is normally API 6D / ISO 14313. ISO 14313:2025 is the third edition, and its stated purpose is to align with the current edition of API Specification 6D. It defines requirements for the design, manufacturing, materials, welding, quality control, assembly and testing of pipeline valves, including ball valves.

Two boundaries: the fact that both are ball valves does not make API 6D clauses applicable to a non-pipeline valve, and vice versa; and API 6D and GOST requirements are not interchangeable by default — which set applies is determined by the contract and project specification.

Standard scope boundaries at a glance

6. Tightness classes and testing

The GOST 9544-2015 class system

GOST 9544-2015 (NEQ to ISO 5208:2008) specifies tightness classes and allowable leakage for pipeline valve closures, covering DN 3–2400 and PN up to 420. The classes are A, AA, B, C, CC, D, E, EE, F and G, where class A is defined as no visible leakage during the test period.

Test conditions:

• Water test: Рисп = 1.1 PN

• Air test: Рисп = 0.6 MPa (for PN > 6); where PN ≤ 6, Рисп = PN

• On customer request, an air test at Рисп = PN (Рр) is also permitted, but the standard limits which classes may be used (for example, at PN ≤ 200 only classes A, AA, B, C, CC and D), with the allowable leakage agreed between the parties

Allowable leakage at DN400 (excerpt):

Source: GOST 9544-2015 Table 2, Annex Б Table Б.1, Annex В Table В.1.

Testing clauses in GOST 28343-89

• Clause 11.1: every valve is pressure tested in accordance with ISO 5208.

• Clause 11.2: where seats are made of elastomeric or polymeric materials, seat leakage shall correspond to class 3 of ISO 5208.

These two clauses state what the standard requires. Again, do not turn them into a claim that a specific product has passed a given class unless a report number can be produced.

Structural reliability requirements

Requirements in GOST 28343-89 that bear directly on trunnion-mounted valves:

• Anti-blowout stem (clause 8.3). The design must prevent the stem from being blown out while the system is pressurised during packing replacement — the packing fasteners themselves do not retain the stem.

• Antistatic construction (clause 8.6). Where required, the valve must have a device ensuring continuous electrical conductivity between stem and body (DN ≤ 50) or between ball and body (larger sizes). The device must sit where it is protected from foreign particles and external corrosion; conductivity testing on dry assembled valves after hydrostatic testing uses a source not exceeding 12 V DC, with discharge at a resistance not exceeding 10 Ω, repeated at least five times; and the design must ensure antistatic continuity can only be removed artificially.

• Direction indication (clause 9.5). The valve must carry a device indicating the direction of the ball port.

• Transport position (clause 13.3). The ball must be in the fully open position for transport unless the design prevents it.

• Marking (clauses 12.2 / 12.3). Body marking includes nominal size (with effective diameter also marked for reduced bore, e.g. DN 80/57), nominal pressure, body material designation, heat number (if required by the customer), manufacturer name or trademark, a flow arrow for unidirectional valves, and the sealing-ring marking for flanges with gasket grooves. The nameplate additionally carries the manufacturer-set pressure or temperature limits, the standard number, and whether antistatic construction is provided.

7. Specification and purchase checklist

Six things to fix before selection

1. Medium and its corrosivity — determines whether 09G2S is suitable, and the seal material

2. Working temperature range and minimum ambient temperature — determines product category, bolting and seals

3. Maximum working differential pressure — determines operating torque and actuator

4. End connection type and standard — flanged, weld-end or fully welded, and to which standard

5. Bore requirement — full or reduced bore, which sets flow capacity

6. Tightness class and test medium — specified to GOST 9544-2015

Documents to request with the order

1. Material certificate, including heat number and the delivery standard and product category relied upon

2. Strength class and impact-test category of the body and bonnet material

3. Pressure test report to ISO 5208 or GOST 33257

4. Tightness class declaration with recorded leakage figures

5. Flange dimension and drilling confirmation drawing, stating the standard and edition used

6. Seat and seal material grade, with the supplier's data sheet

7. Description or verification record for the anti-blowout stem and antistatic construction

8. Confirmation of the face-to-face standard (which ISO 5752 series)

9. Actuator mounting interface dimensions and torque requirement

10. Coating system and transport-condition statement

Where any of these involve measured values (operating torque, test pressure, lead time, service life), the manufacturer's measured or calculated data applies; industry-typical values are not a substitute.

8. Common misreadings

9. FAQ

1. Can a PN 63 valve be used at 63 bar at 200 °C?

Not on that basis. GOST 9544-2015 clause 3.1.12 defines PN at a 20 °C reference. As temperature rises, allowable material stress falls and the permissible working pressure must be reduced. The applicable pressure at a given temperature comes from the design document and the nameplate marking.

2. What is the minimum service temperature of an 09G2S body?

There is no single answer. Under GOST 33260-2015, when 09G2S is used for bodies, bonnets and flanges, the usable temperature varies with the delivery standard and rolled-product category — for example −30 °C, −40 °C and −70 °C correspond to different categories. The complete valve is further limited by bonnet, bolting, gasket and seal materials. The category must be fixed before a temperature can be quoted.

3. What size is DN400 in inches?

DN400 corresponds to NPS 16 (GOST 9544-2015 Annex A, Table A.1). Writing "16-inch" in English-language material is correct.

4. What is the full-bore effective diameter of a DN400 ball valve?

Per GOST 28343-89 Table 3, the DN400 full-bore effective diameter is 380 mm or 375 mm depending on Ру, and 305 mm for reduced bore. Because that standard's Ру series excludes 63, the actual bore of a PN 63 valve should be taken from the manufacturer's drawing and the project specification.

5. Does PN 63 equal ANSI Class 400?

GOST 9544-2015 Annex A, Table A.2 gives that as a reference correspondence. But it is an informative annex, PN and Class are two independent systems with different flange drilling and reference temperatures, and they cannot be directly interchanged. There is also no "Class 63" designation in the ASME system.

6. Why is 63 missing from the GOST 28343-89 nominal-pressure series?

Clause 6 of that standard lists 10, 16, 20, 25, 40, 50 and 100 kgf/cm². PN 63 valves are therefore normally built to project specifications and reference GOST 33259-2015 flanges and API 6D / ISO 14313.

7. How do I choose between trunnion-mounted and floating ball valves?

Choose trunnion-mounted for large sizes, high differential pressure and where an actuator is needed; floating designs are more economical at small and medium sizes with manual operation. DN400 falls in the first group, where a floating design would produce very high operating torque.

8. How much leakage separates GOST 9544 class A and class B at DN400?

Class A is defined as no visible leakage during the test period. Class B allows 4.0 mm³/s in the water test and 120 mm³/s in the air test at 0.6 MPa. Higher classes place correspondingly greater demands on machining accuracy and seal quality.

9. Can 09G2S substitute for Q345 / S345?

Not automatically. Under GOST 19281-2014 the sulfur limits and other requirements differ between 09G2S and S345. Substitution must be agreed in the order; it is not an equivalent swap.

10. What matters for buried installation?

Buried installation normally requires an extended bonnet or extended stem so the valve can be operated and maintained from above ground, together with a confirmed coating system, valve support arrangement, and the ball position during transport and installation (per GOST 28343-89 clause 13.3, the ball should be fully open for transport). The actual arrangement follows the project design and the manufacturer's installation instructions