Quick Answer
Quick Answer
GOST 8731 covers hot-deformed (hot-finished) seamless steel pipes and GOST 8733 covers cold-deformed (cold-drawn or cold-rolled) seamless steel pipes. Both standards share the same material grade system — carbon grades 10, 20, 35, 45 and low-alloy grades 09G2S and 10G2. Grade 20 is the dominant pipe grade and is approximately equivalent to ASTM A106 Grade B and EN P235TR2.
GOST 8731 and GOST 8733 are companion pipe standards that together cover the full production range of seamless steel pipe used in CIS oil and gas infrastructure, power generation, chemical processing, and industrial piping. They are published and maintained as Interstate Standards and apply uniformly throughout Russia, Kazakhstan, Belarus, Azerbaijan, and other CIS member states.
GOST 8731 (Трубы стальные бесшовные горячедеформированные — Seamless hot-deformed steel pipes) covers pipes produced by hot piercing and elongation: hot-extrusion, hot-continuous-rolling (mandrel mill), or hot-push-bench methods. Typical OD range: 25 mm to 530 mm.
GOST 8733 (Трубы стальные бесшовные холоднодеформированные и холоднотянутые — Seamless cold-deformed and cold-drawn steel pipes) covers pipes finish-formed at room temperature. Cold working delivers tighter dimensional tolerances and a superior surface finish. Typical OD range: 5 mm to 250 mm, wall thickness 0.3 mm to 24 mm.
Both standards reference the same underlying material grades; the distinction is fabrication process, not material specification.
Scope and Applicability
GOST 8731
Applies to seamless pipes for:
- General engineering and structural use
- Pipelines for oil, gas, steam, and water
- Boiler and heat-exchanger service (where GOST 8733 or GOST 550 may also be invoked)
- Pressure service at temperatures from −60 °C to +450 °C (material and wall thickness dependent)
GOST 8733
Applies to seamless cold-deformed pipes for:
- Hydraulic and pneumatic lines requiring tight dimensional tolerances
- Heat exchangers and instrument tubing
- Mechanical and structural tubing where OD tolerance and surface quality are critical
- Chemical and petrochemical service at moderate pressures
Both standards exclude welded pipe. For electric-resistance-welded (ERW) pipe in Russia, see GOST 10705; for submerged-arc-welded (SAW) large-diameter pipe, see GOST 20295.
Grade Designation System
GOST 8731/8733 use plain carbon and low-alloy steel grades designated under GOST 1050 (carbon) and GOST 4543 / GOST 19281 (alloy and low-alloy). The grade numbering follows the same convention as GOST 19281 for alloy grades:
- Plain carbon grades (10, 20, 35, 45): the number is the nominal carbon content in hundredths of a percent.
- Low-alloy grades (09G2S, 10G2): letter codes follow the GOST Cyrillic convention (G = Mn, S = Si).
Unlike the St grades of GOST 380, these are quality (спокойная — killed) steels with tightly controlled composition and guaranteed mechanical properties.
Grade Coverage
| Grade | Type | Typical service | Notes |
|---|---|---|---|
| 10 | Carbon | Low-pressure general service, bending, flaring | Excellent formability; not for high-pressure |
| 20 | Carbon | Steam, gas, oil pipelines; most common pipe grade | Approximate equivalent: A106 Gr.B, P235TR2 |
| 35 | Carbon | Higher-pressure mechanical piping; general engineering | Not weld-friendly above 20 mm wall |
| 45 | Carbon | Mechanical tubing, shafts, cylinders | High carbon; limited weldability |
| 09G2S | Low-alloy HSLA | Low-temperature service, pressure vessels | Impact tested to −60 °C |
| 10G2 | Low-alloy | Structural and pressure service, good weldability | Similar to 09G2S but lower Si |
Chemical Composition Requirements
All values are wt%. Ladle analysis governs per GOST 8731 / GOST 8733. Carbon steels per GOST 1050; alloy grades per GOST 19281.
Grade 10
| Element | Limit |
|---|---|
| C | 0.07–0.14 |
| Si | 0.17–0.37 |
| Mn | 0.35–0.65 |
| Cr | ≤ 0.15 |
| Ni | ≤ 0.30 |
| Cu | ≤ 0.25 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
Grade 20
| Element | Limit |
|---|---|
| C | 0.17–0.24 |
| Si | 0.17–0.37 |
| Mn | 0.35–0.65 |
| Cr | ≤ 0.25 |
| Ni | ≤ 0.30 |
| Cu | ≤ 0.25 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
Grade 20 is the closest GOST equivalent to A106 Gr.B. The carbon range overlaps well; manganese is slightly lower in GOST 20 (0.35–0.65 vs. 0.29–1.06 in A106 Gr.B). Both specify P and S ≤ 0.035/0.040.
Grade 35
| Element | Limit |
|---|---|
| C | 0.32–0.40 |
| Si | 0.17–0.37 |
| Mn | 0.50–0.80 |
| Cr | ≤ 0.25 |
| Ni | ≤ 0.30 |
| Cu | ≤ 0.25 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
Grade 45
| Element | Limit |
|---|---|
| C | 0.42–0.50 |
| Si | 0.17–0.37 |
| Mn | 0.50–0.80 |
| Cr | ≤ 0.25 |
| Ni | ≤ 0.30 |
| Cu | ≤ 0.25 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
Grade 09G2S (pipe product)
| Element | Limit |
|---|---|
| C | ≤ 0.12 |
| Si | 0.50–0.80 |
| Mn | 1.30–1.70 |
| Cr | ≤ 0.30 |
| Ni | ≤ 0.30 |
| Cu | ≤ 0.30 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
Grade 10G2
| Element | Limit |
|---|---|
| C | ≤ 0.14 |
| Si | 0.17–0.37 |
| Mn | 1.20–1.60 |
| Cr | ≤ 0.30 |
| Ni | ≤ 0.30 |
| Cu | ≤ 0.30 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
Mechanical Properties
As-Delivered Minimum Mechanical Properties
| Grade | Tensile Str. min (MPa) | Yield Str. min (MPa) | Elongation δ₅ min % | Hardness max (HB) |
|---|---|---|---|---|
| 10 | 340 | 205 | 24 | 149 |
| 20 | 410 | 245 | 21 | 163 |
| 35 | 510 | 305 | 20 | 187 |
| 45 | 590 | 355 | 16 | 207 |
| 09G2S | 490 | 345 | 21 | 178 |
| 10G2 | 460 | 295 | 22 | 163 |
Properties apply to pipes in as-rolled (hot) or cold-drawn + annealed condition. For pipes supplied in normalized condition, properties are similar or slightly improved in toughness.
Wall Thickness Effect on Yield Strength
GOST 8731/8733 do not apply a step-down table for wall thickness in the same manner as GOST 380 plates. However, for heavy-wall pipe (wall > 32 mm), the pipe is typically supplied normalized, and the mill certificate should confirm the supply condition.
Hydrostatic Test Requirements
GOST 8731 and GOST 8733 both require hydrostatic pressure testing of pipes unless the purchaser substitutes non-destructive testing per agreement.
The hydrostatic test pressure (P) is calculated per the standard formula:
P = 2 × S × t / D
Where:
- P = test pressure (MPa)
- S = specified minimum yield strength (MPa) × test factor (0.8 for carbon; 0.75 for alloy)
- t = nominal wall thickness (mm)
- D = outside diameter (mm)
Maximum test pressure is capped at 20 MPa (200 bar) unless otherwise specified. Each pipe must hold the calculated test pressure for a minimum of 10 seconds with no leakage or visible deformation.
Substitution for hydrostatic test: Per GOST 8731 Appendix, ultrasonic testing (UT) per GOST 17410 may substitute for hydrostatic testing when specified on the purchase order. This is standard practice for large-diameter line pipe destined for oil and gas service.
Dimensional Tolerances
GOST 8731 (Hot-Finished)
| Parameter | Normal tolerance | Precision class (П) |
|---|---|---|
| Outside diameter | ±1.25% | ±0.75% |
| Wall thickness (t ≤ 10 mm) | +20% / −15% | +15% / −12.5% |
| Wall thickness (t > 10 mm) | +15% / −12.5% | +12.5% / −10% |
| Length | +50 mm / −0 | As agreed |
GOST 8733 (Cold-Deformed)
| Parameter | Normal tolerance | Precision class (П) |
|---|---|---|
| Outside diameter (≤ 50 mm) | ±0.3 mm | ±0.2 mm |
| Outside diameter (> 50 mm) | ±0.5% | ±0.3% |
| Wall thickness (≤ 3 mm) | ±0.15 mm | ±0.10 mm |
| Wall thickness (> 3 mm) | ±10% | ±7.5% |
Cold-deformed pipes (GOST 8733) carry significantly tighter tolerances than hot-finished equivalents — this is the primary specification driver for instrument tubing, heat exchanger tubes, and hydraulic lines.
GOST Certificate Requirements
A valid certificate for GOST 8731 or GOST 8733 pipe must state:
| Field (Russian) | Field (English) | Required content |
|---|---|---|
| ГОСТ 8731 или 8733 | Standard reference | Specify the correct standard (hot vs. cold) |
| Марка стали | Steel grade | e.g., 20, 09Г2С |
| Плавка № | Heat number | Ladle traceability |
| Химический состав | Chemical composition | C, Si, Mn, P, S (+ alloying for low-alloy grades) |
| Механические свойства | Mechanical properties | UTS, YS, elongation from test pieces |
| Гидравлическое испытание | Hydrostatic test | Test pressure value and result (выдержала / passed) |
| Размеры | Dimensions | OD × wall thickness × length (mm) |
| Класс точности | Precision class | Normal or П (precision) |
| Масса | Mass | Total weight of the shipment lot |
| Штамп и подпись | Stamp and signature | Mill QC stamp |
Cross-Standard Equivalents
| GOST Grade | ASTM | EN (pipes) | DIN (legacy) | Notes |
|---|---|---|---|---|
| Grade 20 | A106 Gr.B | EN 10216-1 P235TR2 | St 37.0 | Carbon overlap; verify Mn (GOST Mn slightly lower) |
| Grade 20 (boiler) | A53 Gr.B | EN 10216-2 P265GH | St 44.0 | For elevated-temp boiler service, composition is adequate |
| Grade 10 | A106 Gr.A | EN 10216-1 P195TR1 | St 35.0 | Lower carbon; cold-forming and flaring applications |
| Grade 35 | A519 Gr.1035 | EN 10297-1 E355 | Ck35 | Mechanical/structural tubing; not pressure pipe |
| Grade 45 | A519 Gr.1045 | EN 10297-1 E420 | Ck45 | Mechanical tubing; limited weldability |
| 09G2S | A333 Gr.6 (approximate) | EN 10216-3 P355NL1 | — | Low-temp service; impact test required |
| 10G2 | A333 Gr.1 (approximate) | EN 10216-3 P275NL1 | — | Lower strength than 09G2S; better weldability |
Grade 20 is the most commonly cross-referenced GOST pipe grade. Accept as A106 Gr.B equivalent only when the certificate confirms: C 0.17–0.24, YS ≥ 245 MPa, UTS ≥ 410 MPa, and hydrostatic test passed. A106 Gr.B mandates 0.29–1.06 Mn; GOST 20 allows lower Mn (0.35–0.65) which is still within A106's compositional envelope.
MTC Verification Checklist
- Correct standard cited: GOST 8731 for hot-deformed, GOST 8733 for cold-deformed
- Steel grade clearly stated (20, 09G2S, etc.) with Cyrillic rendering if on original certificate
- OD × wall thickness × length match purchase order dimensions
- Precision class (normal or П) confirmed
- Chemical analysis within grade limits (check C range — Grade 20: 0.17–0.24%)
- UTS ≥ 410 MPa, YS ≥ 245 MPa, elongation ≥ 21% for Grade 20
- Hydrostatic test pressure stated and result recorded (or UT substitution confirmed)
- Heat number on certificate matches physical pipe markings (end stamping or paint stencil)
- For low-temperature service (09G2S): impact test results at required temperature present
Frequently Asked Questions
What is the difference between GOST 8731 and GOST 8733?
The difference is the manufacturing process. GOST 8731 covers hot-deformed pipes: the pipe is formed while the steel is above its recrystallization temperature (~950–1250 °C). GOST 8733 covers cold-deformed pipes: the pipe is drawn or rolled at room temperature. Cold-deformed pipes have tighter dimensional tolerances, a better surface finish, and slightly higher mechanical properties due to work hardening, but they are more expensive to produce. Both standards use the same material grade designations.
Is GOST Grade 20 the same as ASTM A106 Grade B?
They are broadly equivalent for most piping applications. Both are killed medium-carbon steels with similar yield (245 MPa min), tensile strength (410 MPa min), and elongation requirements. The key difference is manganese: A106 Gr.B allows up to 1.06% Mn while GOST 20 is limited to 0.35–0.65%. In practice, this rarely affects fitness for service, but it means a GOST 20 pipe may not formally comply with A106 Gr.B's composition requirements. For project specifications requiring A106 Gr.B compliance, request dual-certified material or an equivalency engineering justification.
What does hydrostatic testing under GOST 8731 involve?
Every pipe must be hydrostatically tested at a calculated pressure based on the pipe's yield strength, wall thickness, and outside diameter. The formula P = 2St/D gives the test pressure (capped at 20 MPa). The pipe holds this pressure for at least 10 seconds. No leakage or deformation is permitted. The test pressure value and the result (выдержала — withstood) must appear on the certificate. Purchasers may substitute ultrasonic testing per GOST 17410 when agreed with the mill.
Can GOST 8731 Grade 20 be used for low-temperature service?
Grade 20 is not designed for sub-zero service. Its impact properties are not guaranteed at temperatures below 0 °C. For service down to −40 °C, specify Grade 09G2S under GOST 8731/8733 with delivery category specifying low-temperature impact testing. For service below −40 °C, consult GOST 550 (boiler and heat-exchanger tube in low-alloy steels) or specialty low-temperature pipe specifications.
How do I read the pipe dimensions from a GOST 8731 certificate?
GOST 8731 pipes are dimensioned as OD (внешний диаметр) × wall thickness (толщина стенки) × length (длина) in millimeters. For example, "108 × 8 × 6000" means 108 mm OD, 8 mm wall, 6 metre length. The certificate should state both nominal dimensions and the applicable precision class (normal or П) which determines the acceptable tolerance on each dimension. Check OD tolerance: for hot-finished pipe ≤ 273 mm OD at normal precision, the OD tolerance is ±1.25%.
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