GOST 2.312 and ISO 2553: reading older drawings
Equipment built to Soviet drawings is still in service across Europe, and the symbols on those drawings follow a different logic from the one in ISO 2553. The differences are systematic, which makes them learnable.
Different logic, not just different marks
ISO 2553 draws the weld: the symbol is a picture of the joint cross-section, and the dimensions sit around it. GOST 2.312 names the joint: the reference calls out a joint type from a catalogue of standard preparations in a companion standard, and that catalogue defines the geometry.
So a GOST reference such as С17 means "butt joint number 17"
from GOST 5264 — a V preparation with a specified angle, gap and root face.
You cannot read the geometry off the drawing; you look it up.
The visible differences
| Element | GOST 2.312 | ISO 2553 |
|---|---|---|
| Side of the joint | Symbol above the line = arrow side; below = other side | Continuous line = arrow side; dashed = other side |
| Joint type | Letter and number code: С (butt), Т (tee), У (corner), Н (lap) | Drawn symbol: V, triangle, square |
| Preparation | Defined by the standard joint number | Dimensioned on the drawing |
| Fillet size | Leg, written as К with the size | Throat a, or leg z |
| All round | Circle at the elbow | Circle at the elbow |
| Field weld | Flag | Flag |
Note the first row: the "above the line" convention in GOST matches AWS, not ISO. A welder used to AWS will read the side correctly on a GOST drawing by accident, and a welder used to ISO system A will read it backwards.
The joint-type letters
- С — butt joint (stykovoye). GOST 5264 for manual arc welding, GOST 14771 for gas-shielded.
- Т — tee joint.
- У — corner joint.
- Н — lap joint.
- К before a number — the fillet leg size, so
К6is a 6 mm leg, equivalent to ISOz6and a throat of about 4.2.
Working from an old drawing
Three steps. Identify the joint code and find the preparation in the relevant GOST table — the angle, gap and root face are there, not on the drawing. Convert the fillet size: GOST gives the leg, so divide by 1.41 if your procedure works in throat. And check the material: the steel grade will be a GOST designation, so run it through the steel grade equivalents table before choosing a consumable.
One caution worth repeating: an equivalence table matches strength, not chemistry. Before welding a repair on unknown old steel, get the composition and put it through the carbon equivalent calculator — old structural steel is frequently higher in carbon than its modern nominal equivalent.
Frequently asked questions
Where would I still meet a GOST drawing?
Wherever equipment built in the former Soviet Union is being repaired or modified — presses, cranes, boiler plant, agricultural machinery, railway stock. Drawings outlive the factories that made them, and a repair to an old machine is often done from the original documentation.
Can I convert a GOST symbol to ISO?
Not mechanically. GOST encodes the joint type and preparation in a designation from a table of standard joints, where ISO draws the weld shape. Converting means looking up what the GOST code specifies and then expressing that geometry in ISO terms — a translation, not a substitution.
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