IS 7307 Part 1 : 1974Radiographic Examination of Fusion Welded Butt Joints in Steel Plates - Part 1: Method for Test

IS 7307 Part 1:1974 specifies the method for radiographic examination of fusion-welded butt joints in steel plates — the NDT procedure (technique, setup, film/IQI, sensitivity) for detecting internal weld defects in critical steel welds: tanks, pressure parts, structural butt welds, penstocks, pipelines.

It is read with the welding/QA stack:

• IS 822 — procedure for inspection of welds (the parent inspection code) · IS 814 — MMAW electrodes
• IS 9595 — metal-arc welding recommendations · IS 7310 / IS 7318 — acceptance standards / fusion-weld radiograph interpretation
• IS 800 — steel construction (where weld NDT is invoked) · IS 2825 / IS 803 — pressure vessels / tanks

Radiography detects internal volumetric and planar defects by the differential X-/γ-ray absorption captured on film/detector. IS 7307 Part 1 fixes the variables that make a radiograph *valid*:

• Source & energy (X-ray kV / γ-source: Ir-192, Co-60) appropriate to the plate thickness
• Geometry — source-to-film distance, single/double-wall technique, to control geometric unsharpness
• Image Quality Indicator (IQI / penetrameter) — the wire/step-hole gauge that *proves the achieved sensitivity*; the radiograph is only acceptable if the required IQI sensitivity is visible
• Film density & processing within limits
• Coverage & overlap of the weld length

The defects revealed — porosity, slag inclusions, lack of fusion, lack of penetration, cracks, undercut — are then graded against the *acceptance* standard (IS 7310/IS 7318 or the contract), which is a *separate* document from this method.

Scenario: full-penetration butt weld in a steel plate, radiographed to IS 7307 Part 1.

Step 1 — technique: select source/energy for the plate thickness; set source-to-film distance for acceptable geometric unsharpness; single-wall single-image technique.

Step 2 — IQI: place the required wire/hole IQI; expose.

Step 3 — validity check: the radiograph is *only usable* if the specified IQI sensitivity is clearly visible and film density is within range — otherwise re-shoot. (Skipping this is the No.1 NDT error: an under-exposed film 'shows no defects' because it can't.)

Step 4 — interpretation: identify and size indications (porosity, slag, LOF, LOP, crack).

Step 5 — acceptance: grade against the acceptance standard (e.g. IS 7310/IS 7318 or the project spec) — *cracks/lack-of-fusion are typically rejectable regardless of size*. Repair + re-radiograph the repaired length. IS 7307 told you *how to see*; the acceptance code tells you *pass/fail*.

1. No / wrong IQI — the cardinal sin. Without the required IQI sensitivity demonstrated, the film is invalid; a 'clean' under-sensitive radiograph hides exactly the defects you were testing for.

2. **Confusing the *method* with the *acceptance* standard.** IS 7307 Part 1 is *how to radiograph*; pass/fail comes from IS 7310/IS 7318 or the contract — quoting only IS 7307 leaves acceptance undefined.

3. Inadequate coverage/overlap. Defects at un-radiographed weld lengths/overlaps pass by omission — specify % coverage and overlap.

4. Wrong source/energy or density. Too-hard or under-exposed shots lose sensitivity to fine planar defects (LOF/cracks).

5. Not re-radiographing repairs. A repaired length must be re-shot; assuming the repair is good is unverified.

• IS 822 — code of procedure for inspection of welds
• IS 7310 / IS 7318 — acceptance / interpretation of radiographs of fusion welds
• IS 4853 / IS 2595 — radiographic testing practice references
• IS 9595 — metal-arc welding recommendations · IS 814 — electrodes
• IS 800 — steel construction · IS 2825 / IS 803 — pressure vessels / tanks (where RT is mandatory)

IS 7307 Part 1 is reaffirmed and broadly aligned with international RT practice (ISO 17636 / ASME V); fabricators' procedures typically cite it alongside the ISO/ASME equivalents, which is acceptable when cross-referenced. Radiography remains the definitive volumetric NDT for critical butt welds (tanks, penstocks, pressure parts, important structural splices), complementing UT.

The single discipline that determines whether RT is meaningful is the IQI/sensitivity check — a radiograph without a demonstrated, in-range IQI is not evidence of anything, yet 'no defects on the film' from an under-sensitive shot is the recurring way bad welds get passed. The practitioner contract: specify the *acceptance* standard explicitly (IS 7307 alone doesn't pass or fail anything), mandate IQI sensitivity and film density, define coverage/overlap, and require re-radiography of all repairs — then the NDT actually protects the joint instead of papering over it.