1. Design Standards
Russian malleable iron pipe fittings are designed according to the following standards:
– GOST 8944-75
Malleable Iron Threaded Fittings (Parallel Thread).
Applicable for piping systems with nominal pressure ≤1.6 MPa (16 bar), covering dimensions and tolerances for elbows, tees, caps, etc.
– GOST 8954-75
Malleable Iron Threaded Fittings (Taper Thread).
Used for higher sealing requirements, featuring tapered threads (GOST 6211-81).
2. Thread Standards
Pipe fittings use two thread types:
– Parallel Thread (Non-Sealing):
GOST 6357-81
– 55° thread angle, straight threads, requires sealing materials (e.g., PTFE tape).
– Example marking: G1½ (equivalent to BSPP).
– Taper Thread (Sealing):
GOST 6211-81
– 55° thread angle, 1:16 taper, self-sealing.
– Example marking: R1½ (equivalent to BSPT).
3. Material Standards
Malleable iron fittings comply with:
– GOST 1215-79
General Specifications for Malleable Cast Iron.
– Material grades: E.g., KCh 30-6 (tensile strength ≥300 MPa, elongation ≥6%).
– Chemical composition: Low carbon (C≤2.9%), low silicon (Si≤1.4%), annealed for ductility.
– Mechanical properties: Must pass flattening and bending tests.
4. Types of Fittings
Common malleable iron threaded fittings include:
| Type | Russian Name | Function | Example Spec. |
| Elbow | Угольник (Ugol’nik) | Changes flow direction (90°, 45°) | GOST 8944-75 G1 |
| Tee | Тройник (Troynik) | Splits/merges flow (equal/reducing) | GOST 8944-75 G1½×¾ |
| Cross | Крестовина (Krestovina) | Four-way connection | GOST 8944-75 G1 |
| Cap | Заглушка (Zaglushka) | Seals pipe ends | GOST 8944-75 G2 |
| Union Nut | Сгонная муфта (Sgonnaya mufta) | Removable connection (with gasket) | GOST 8954-75 R1 |
| Reducer | Переходник (Perekhodnik) | Connects different pipe sizes | GOST 8944-75 G1½×1 |
5. Applications
– Low-pressure fluids: Plumbing, gas (with sealant), compressed air.
– Building systems: Sanitary fixtures, fire sprinklers (non-high-pressure).
– Industrial equipment: Instrumentation, hydraulic circuits (with O-rings).
6. Comparison with Other Standards
| Parameter | Russian (GOST) | International (ISO/BSP) | American (NPT) |
| Thread Type | GOST 6357-81 (Parallel) | ISO 228-1 (BSPP) | ASME B1.20.1 (NPS) |
| Sealing | Non-sealing (needs gasket) | Non-sealing | Tapered (NPT) self-seals |
| Pressure | ≤1.6 MPa | ≤16 bar | ≤3000 psi |
Key Notes
– Sealing: Taper threads (GOST 6211-81) are preferred for high-pressure/temperature.
– Material alternatives: Galvanized malleable iron (GOST 9.307-89) for corrosive environments.
7.Russian Cylindrical Pipe Thread Standards & Applications
1. Russian Cylindrical Pipe Thread Standard (GOST 6357-81)
– Standard Name: GOST 6357-81 –”Straight (Parallel) Pipe Threads for Cylindrical Connections.”
– Thread Type:
– Non-pressure-tight (non-sealing) cylindrical thread (similar to ISO 228-1 / BSPP).
– 55° thread angle, measured in nominal pipe size (e.g., G1″).
– Key Features:
– Requires additional sealing (e.g., PTFE tape, gaskets) for leak-proof connections.
– Compatible with BSPP (British Standard Pipe Parallel) and ISO 228-1.
– Marking Example:
– G1/2 (½-inch nominal pipe thread).
– GOST 6357-81 G1″ (1-inch thread per GOST standard).
2. Applications of GOST 6357-81 Threads
This standard is widely used in low-pressure, non-sealed, or sealant-assisted connections, including:
① Low-Pressure Fluid Systems
– Plumbing: Water supply & heating pipes (with sealant).
– Pneumatics: Compressed air lines in industrial tools.
– Irrigation: Low-pressure water distribution.
② Mechanical & Equipment Connections
– Instrumentation: Pressure gauges, thermometers (e.g., G1/4, G1/2 ports).
– Hydraulics: Low-pressure hydraulic fittings (with O-rings).
– General machinery: Non-pressure structural assemblies (covers, brackets).
③ Industrial & Maintenance Uses
– Chemical plants: Non-corrosive fluid transport (vent/drain pipes).
– Food processing: Sanitary pipe joints (removable for cleaning).
– Retrofitting: Replacing legacy Soviet/Russian threaded fittings.
④ Where Frequent Disassembly is Needed
– Filters/valves: Regularly serviced components.
– Lab equipment: Modular fluid system connections.
⚠ Important Notes
– Not for high-pressure/temperature sealing (use GOST 6211-81 taper threads instead).
– Sealant-dependent: PTFE tape or liquid sealant is mandatory.
– Global compatibility: Matches BSPP (UK/EU), PF (Japan), and GB 7307 (China).
For exact pressure/temperature limits, consult GOST 6357-81 technical tables.
