Steel repair scope is built from measurement, not from opinion. Ultrasonic thickness gauging compared against allowable diminution turns “the hull looks tired” into a plate-by-plate renewal list with an area figure — the only basis on which a repair can be priced, tendered and controlled.
What gauging actually measures
Ultrasonic testing measures remaining metal thickness at defined points across shell plating, decks, bulkheads, internal structure and, where accessible, tank boundaries. The reading is compared with two references: the original as-built thickness from the approved drawings, and the classification society’s allowable diminution for that member. Where remaining thickness falls below the allowable limit, the member requires renewal; where it approaches it, the member requires monitoring or partial renewal depending on the class rules and the survey being carried out.
The output is only useful if it is located. Readings tabulated without positions on the shell expansion cannot be converted into a work scope. A good report shows where every reading was taken, so a repair plan can be drawn on the structure.
Reading a gauging report as an owner
| What to look at | Why |
|---|---|
| Coverage — how many points, where | Sparse coverage hides localised wastage; dense coverage in one area may be missing the problem elsewhere |
| Pattern of loss | General diminution is a coating and age story; localised pitting is a specific mechanism worth diagnosing before renewing |
| Distance from the allowable limit | Members close to the limit will fail at the next survey; renewing them now, while access is open, is usually less costly |
| Internal structure readings | Frames, brackets and stiffeners waste faster than plating in wet spaces and are frequently under-sampled |
The renewal sequence
- Mark out. Condemned areas marked on the structure from the gauging plan, with the surveyor agreeing the extent before cutting.
- Support and access. Staging, temporary support where structure is being removed, ventilation and safety arrangements for hot work.
- Cropping. Condemned plate cut out to clean boundaries, avoiding weld-on-weld and respecting minimum distances from existing seams.
- Insert fitting. New plate of the approved grade and thickness fitted, with edge preparation to the approved welding procedure.
- Welding. By qualified welders to the approved procedure, with sequence controlled to limit distortion.
- Testing. Non-destructive testing to the extent required, and tank or tightness testing where boundaries have been penetrated.
- Reinstatement. Surface preparation and coating of the repaired area and its heat-affected surroundings, plus any insulation, piping or fittings removed for access.
Why access dominates the cost
The steel is often the low-costest part of a steel repair. Getting to it is not. Renewal inside a tank requires cleaning, gas-freeing, ventilation, staging, lighting and continuous safety supervision; renewal behind machinery or insulation requires removal and reinstatement of everything in front of it. This is why two repair scopes of identical area can differ several-fold in price, and why an owner comparing quotations must compare scope locations, not only areas.
Controlling scope growth
Steel repair grows for two legitimate reasons: cropping reveals adjacent wastage that gauging did not sample, and removing structure exposes condition that could not previously be seen. Both are real. What must not be tolerated is undocumented growth. The control is a written variation procedure — work outside the agreed scope is described, priced and approved before it starts, as set out in our article on contract structure.
The second control is sampling discipline: where the gauging report shows a pattern of loss, extend sampling in that area before the vessel is docked, not after cutting begins.
Coating is part of the repair
A renewed plate with a poor coating will waste again. The repair specification should state surface preparation standard, coating system, film thickness, and the environmental limits for application — and the yard should record conditions and thickness per area. In a humid climate this is the difference between a repair that lasts a survey cycle and one that does not, as discussed in our article on steel construction discipline.
Where this fits
Gauging results, together with the class status and outstanding conditions of class, are the two documents that begin every docking scope on our repair and refit page. Send them — or the vessel particulars if gauging is not yet done — to sales@komodoluxury.com or +62 811-3823-875. Scopes are issued in USD, with contracts from PT Komodo Galangan Nusantara.
Planning renewal across two survey cycles
The most economical repair strategy is rarely “renew exactly what is condemned today”. Members close to their allowable limit will be condemned at the next survey, and renewing them now — while access is open, staging is up and the vessel is already out of the water — avoids paying for access twice. A good gauging report makes that judgement possible by showing not only what has failed but how close everything else is to failing.
The counterweight is capital: bringing renewal forward accelerates spending. The balance depends on how long the owner intends to keep the vessel, which is why this conversation belongs with the owner rather than with the yard.
Frequently asked questions
What is a thickness measurement report?
A record of ultrasonic readings taken across the hull structure, compared against the original as-built thickness and against the classification society’s allowable diminution. Plotted on the shell expansion, it converts subjective hull condition into a plate-by-plate renewal list.
Who performs the gauging?
An approved thickness measurement service provider, with the class surveyor in attendance or reviewing the results. Readings taken informally by the yard are useful for planning but are not the basis for a class decision.
How is renewal priced?
Normally by area or weight of steel renewed, plus access, staging, cleaning and coating reinstatement. The steel itself is rarely the largest component — access and reinstatement often exceed it, which is why scope location matters as much as scope size.