IS 816:1969 is the Indian Standard (BIS) for use of metal arc welding for general construction in mild steel. IS 816 is India's primary welding code for structural steel construction. It covers joint design, electrode selection, welding procedures, and inspection/acceptance criteria for manual metal arc welding of mild and medium carbon steels. Referenced by IS 800 (steel design code) for all welded connections.
Code of practice for manual metal arc welding (MMAW/SMAW) of mild steel in general construction, covering joint design, electrode selection, welding procedure, inspection, and defect acceptance criteria.
Key design values for metal arc welding in mild steel, including permissible stresses, fillet and butt weld geometry, and workmanship tolerances.
| Reference | Value | Clause |
|---|---|---|
| Applicable Parent Metal— IS 226 is now superseded by IS 2062. Verify project specs. | Mild Steel (IS 226) | Cl. 3.1 |
| Recommended Electrode Type— For welding steel conforming to IS 226. | Covered electrodes, Class A | Cl. 4.1.1 |
| Permissible Shear Stress (Shop Weld)— Working Stress Method. For design, refer to IS 800:2007. | 108 MPa | Cl. 8.3 (Table 1) |
| Permissible Axial Stress (Shop Weld)— For butt welds. For design, refer to IS 800:2007. | 150 MPa | Cl. 8.3 (Table 1) |
| Permissible Stress Reduction (Field Weld)— For Class A electrodes. Use 90% for Class B. | Use 80% of shop weld stress | Cl. 8.3, Note 1 |
| Permissible Stress Increase (Wind/EQ)— When combination includes wind or earthquake loads. | +25% | Cl. 8.4 |
| Effective Throat Thickness (Fillet)— 's' is the size of the weld. 'k' varies with fusion face angle. | k × s (k=0.7 for 60-90°) | Cl. 9.2.1 (Table 2) |
| Effective Throat Thickness (Butt)— Applies to a complete penetration butt weld. | Thickness of thinner part | Cl. 9.1 |
| Min. Fillet Weld Size— For structural work, 5 mm is often preferred as a practical minimum. | 3 mm | Cl. 10.2.1 |
| Max. Fillet Weld Size (at Square Edge)— 't' is the thickness of the plate edge. | t - 1.5 mm | Cl. 10.2.2.1 |
| Max. Fillet Weld Size (at Round Edge)— 't' is the thickness of the plate. | ¾ × t | Cl. 10.2.2.2 |
| Min. Effective Weld Length— Shall not be less than 4 times the weld size 's'. | 4 × s | Cl. 10.2.3 |
| Min. Intermittent Weld Length— Whichever is more. 's' is the weld size. | 40 mm or 4 × s | Cl. 10.2.4.1 |
| Max. Intermittent Weld Spacing (Compression)— Whichever is less. 't' is the thickness of the thinner plate. | 200 mm or 12 × t | Cl. 10.2.4.2 |
| Max. Intermittent Weld Spacing (Tension)— Whichever is less. 't' is the thickness of the thinner plate. | 200 mm or 16 × t | Cl. 10.2.4.2 |
| End Returns Length— Required at ends of tension/compression members. | ≥ 2 × s | Cl. 10.2.5 |
| Min. Lap for Lap Joints— 't' is the thickness of the thinner part. Not less than 25 mm. | 4 × t | Cl. 10.3.1 |
| Max. Gap Between Members (Fillet Weld)— If >1.5mm & <3mm, increase weld size by gap amount. | 1.5 mm | Cl. 12.4.1 |
| Tack Weld Min. Length— Whichever is less. 't' is the thickness of the part. | 40 mm or 4 × t | Cl. 12.5 |
| Tack Weld Max. Spacing— 't' is the thickness of the thinner part. | 16 × t | Cl. 12.5 |
| Max. Permissible Undercut— For dynamically loaded structures. 1.5 mm for static structures. | 0.8 mm | Cl. 14.1.1 (a) |
IS 816:1969 is the code of practice for the use of metal-arc (manual metal-arc / shielded-metal-arc) welding for general construction in mild steel — joint design, electrode selection, welding procedure, workmanship and inspection for welded mild-steel structures. It is the welding-practice companion to the steel design code IS 800: IS 800 designs the welded connection, IS 816 governs how it is actually made.
It sits in the structural-steel stack:
A welded connection is only as good as the joint design, the consumable, the procedure and the inspection — IS 816 ties these together for mild steel:
The engineering point: the weld is a fabricated structural element, not a given — the *fillet weld effective throat and length* and *full fusion* are what carry the load, and the recurring failures (undersized/under-length fillets, lack of fusion/penetration, distortion, unqualified welders) are workmanship issues IS 816 + procedure/welder approval + inspection exist to control.
Scenario: a fillet-welded structural mild-steel connection designed to IS 800.
Step 1 — joint & weld size from design: take the required weld type, size and effective length from the IS 800 connection design; detail edge preparation for fusion.
Step 2 — consumable: matching-strength covered electrode to IS 814, correct type/size, dry and at the right current/polarity.
Step 3 — qualified procedure & welder: an approved welding procedure and a qualified welder (procedure/welder approval standards); pre-heat/sequence as required to control distortion and cracking.
Step 4 — execute with workmanship control: clean joint, correct technique, inter-run cleaning, run sequence to limit residual stress/distortion.
Step 5 — inspect to acceptance: visual + NDT for lack of fusion/penetration, undercut, porosity, cracks; accept against the specified level — the weld is verified, not assumed.
The connection carries the IS 800 design force only if the throat/length and fusion are actually achieved — which is precisely what IS 816 practice + inspection secure.
1. Undersized / under-length fillet welds. The effective throat × length carries the load — short or thin fillets are a top cause of weld-connection failure.
2. Lack of fusion / incomplete penetration. Poor edge prep, wrong current/technique — a hidden, serious defect; demands proper procedure and NDT.
3. Wrong / damp electrodes. Non-matching or moisture-contaminated electrodes (esp. low-hydrogen) → weak or cracked welds; use the right IS 814 electrode, kept dry.
4. Unqualified procedure / welders. Welds made without an approved procedure and qualified welders are unverified structural elements.
5. No inspection / distortion control. Skipping visual+NDT, or no run sequence/pre-heat, leaves defects and locked-in distortion/residual stress undetected.
IS 816 is old (1969) but remains the Indian practice code for mild-steel arc welding in general construction, and its core lesson endures: a weld is a fabricated structural element whose capacity is made on site, not given on a drawing. IS 800 designs the connection; whether it actually carries the force depends on the fillet throat and length, full fusion, the right dry electrode, a qualified procedure and welder, and inspection — and the chronic real-world failures (undersized/short fillets, lack of fusion/penetration, damp electrodes, unqualified welders, no NDT) are exactly the workmanship items IS 816 plus the procedure/welder-approval and weld-inspection standards exist to control. For modern fabrication some provisions are read with updated welding/inspection standards, but the discipline is unchanged: design the weld, qualify the procedure and people, control the workmanship, and inspect it — never assume it.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Min fillet (10mm plate) | 3 mm | 3 mm (1/8") | AWS D1.1 Table 7.7 |