RT Film Length Calculator

Formula used

This calculator models film usage along the weld axis with planned overlap and margins. It assumes each exposure consumes a film length equal to the selected sheet long side (or your custom length).

• L_inspected = L_weld + 2·M
• L_effective = L_film · (1 − O) where O = overlap% / 100
• N_exp = ceil( L_inspected / L_effective )
• Film_base = N_exp · L_film · (welds) · (sides)
• Film_total = Film_base · (1 + W) where W = waste% / 100

How to use

1. Enter the total weld length and select its unit.
2. Set the number of welds and the inspection sides.
3. Select a standard sheet size or enter a custom film length.
4. Choose overlap percentage and end margins for positioning.
5. Add a waste allowance for retakes and handling.
6. Optionally enter roll length to estimate the number of rolls.
7. Press Calculate to see results, then export CSV or PDF.

Example data table

Example figures are rounded planning values; site technique can change coverage.

Professional notes for RT film length planning

1) Scope of film planning on construction sites

Radiographic testing (RT) consumes film in predictable increments when the plan matches field reality. A practical estimate links weld length, exposure coverage, overlap, and positioning allowances. This calculator converts those choices into a single film-length total for purchasing and logistics.

2) Inputs that drive film usage

Total weld length is the base driver, then weld count and inspected sides scale the requirement. If a joint is inspected from two sides, exposures and film usage typically double. End margins also add length for setup space and edge coverage.

3) Selecting sheet size versus custom length

Common sheet formats such as 10×12 in or 14×17 in are convenient for estimating coverage along the weld. When your technique uses cut strips or a different effective length, the custom option is better. Use the length that actually runs along the weld axis.

4) Overlap and effective coverage

Overlap protects continuity between adjacent exposures and reduces the risk of gaps. The calculator applies overlap as a reduction in effective coverage: L_effective = L_film(1−O). For example, 12 in film with 10% overlap gives 10.8 in usable coverage per exposure.

5) Margins, clamps, and practical positioning

Leader and trailer margins are planned space that prevents edge cut‑off and supports consistent placement. A common starting point is 20–30 mm per end, then adjust for clamps, identification markers, or curvature. Small margin changes can add exposures on shorter welds.

6) Waste and retake allowance

Waste allowance captures trimming, handling damage, and retakes from density, contrast, or motion issues. Many teams begin with 5–10% for steady work, then refine using job history. Difficult access or variable conditions can justify higher allowances.

7) Roll estimation for procurement

If you buy film in rolls, the total length is more actionable as an estimated roll count. Enter roll length to translate total film into rolls required. This helps avoid partial stock-outs and reduces mid-shift delays when multiple crews share inventory. Tracking roll consumption per shift also highlights process losses and supports better retake controls later.

8) Field example for quick validation

Suppose 12 m of weld is inspected on one side using 14×17 in sheets, 15% overlap, 25 mm margins, and 8% waste. The calculator yields a whole-number exposure count and a planning total near 5 m. Compare with prior jobs to calibrate assumptions.

FAQs

1) What does “film length per exposure” represent?

It is the film dimension aligned with the weld axis for one exposure. For a sheet, this calculator assumes the long side runs along the weld unless you use the custom option.

2) Why is overlap applied as a percentage?

Overlap varies by technique and crew practice. Using a percentage makes it easy to apply the same planning rule across different sheet lengths while reflecting consistent coverage continuity between exposures.

3) How do end margins affect the result?

Margins increase the inspected length per weld, which can push the exposure count up to the next whole number. This is most noticeable on short welds where one extra exposure changes totals significantly.

4) Should I enter total weld length or length per weld?

Either works if you are consistent. If you enter length per weld, also enter the number of welds. The calculator multiplies exposures by weld count and inspected sides.

5) What waste percentage is reasonable for planning?

Many projects start at 5–10% and adjust from historical retake rates. Use higher values for restricted access, variable power, complex geometry, or when multiple crews handle film.

6) Can this estimate rolls needed for procurement?

Yes. Add the roll length to compute an estimated roll count using the calculated total film length. This converts a technical quantity into a purchasing-friendly number.

7) Is the example table a standard requirement?

No. It is a reference to help validate your inputs. Your site technique, identification practices, and acceptance criteria may change overlap, margins, and waste allowances.