Welding, Plate Replacement & NDT

OVERVIEW

Welding and structural plate replacement during a yacht refit must be treated as controlled technical operations rather than simply fabrication work.

The Project Manager does not determine how a qualified welder performs the weld. The PM's responsibility is to ensure that the repair has a defined technical basis, the correct materials are used, the welding personnel are suitably qualified, the applicable procedure is available, Class involvement is established where required and inspection hold points are respected.

The objective of this module is to provide the Project Manager with sufficient understanding to control structural welding and plate replacement intelligently without assuming the role of the welding engineer, Class surveyor or qualified welder.

KEY RESPONSIBILITIES

• Establish the extent and technical basis of the structural repair

• Confirm the latest approved drawing or repair sketch

• Verify replacement material grade and thickness

• Maintain material traceability where required

• Confirm the applicable Welding Procedure Specification

• Verify that the welder is qualified for the required process, material and welding position

• Coordinate Class review and survey attendance where required

• Establish inspection and hold points before work begins

• Confirm hot-work and QHSE controls are in place

• Identify cables, pipework, insulation and equipment behind or adjacent to the work

• Coordinate temporary structural support where required before cutting

• Control crop-out and inspection of exposed structure

• Ensure additional deterioration is assessed before continuing

• Coordinate replacement-plate preparation and fit-up

• Confirm joint preparation and alignment before final welding

• Understand the purpose of the selected welding process without directing the welder's technique

• Monitor welding progress against the agreed repair sequence

• Coordinate visual examination and required NDT

• Ensure defects identified by NDT are properly repaired and re-examined

• Coordinate watertightness or pressure testing where applicable

• Maintain a complete structural-repair record

WPS, WELDER QUALIFICATION & WELDING PROCESS

Before structural welding begins, the Project Manager should understand three separate controls:

• the material and joint that must be welded

• the approved Welding Procedure Specification

• the qualification of the person carrying out the weld

These controls are related, but they are not interchangeable.

Welding Procedure Specification — WPS

The Welding Procedure Specification defines how a particular weld is to be carried out.

Depending on the material and joint, the WPS may define:

• parent material

• material thickness range

• joint configuration

• edge preparation

• root gap

• welding process

• filler material or electrode

• shielding gas where applicable

• welding position

• preheat temperature where required

• interpass temperature

• current and voltage range

• heat input

• number and sequence of weld passes

• backing arrangement where applicable

• post-weld requirements

The Project Manager does not create or modify the WPS. The PM should confirm that the procedure being used is appropriate for the actual repair.

Welder Qualification

A welder being qualified does not mean that the person is automatically qualified to weld every material, thickness, process and welding position.

The qualification should cover the work being undertaken.

The PM should therefore verify, where applicable:

• welder identity

• qualification certificate

• welding process

• material group

• thickness range

• welding position

• qualification validity

• Classification or approval requirements

A welder qualified for carbon-steel structural work should not automatically be assumed competent or approved for aluminium, stainless steel, copper alloy or another specialist material.

COMMON WELDING PROCESSES

The welding process should be selected by the welding specialist according to the material, joint configuration, access, approved WPS and required quality.

SMAW — Shielded Metal Arc Welding

Often referred to as stick welding or electrode welding. In French yard terminology it may informally be described as welding with a baguette.

It is portable and can be useful for structural repair, restricted access and work where large welding equipment is impractical.

GMAW — MIG / MAG

Gas Metal Arc Welding uses continuously fed wire and shielding gas.

It can provide high productivity and good control for fabrication and structural work, but the shielding gas must be protected from excessive air movement or wind.

GTAW — TIG

Gas Tungsten Arc Welding provides precise control of the weld pool and heat input.

It is widely used for stainless steel, aluminium, copper alloys and detailed fabrication where controlled weld quality is required.

FCAW — Flux-Cored Arc Welding

Flux-Cored Arc Welding can provide relatively high deposition rates and is commonly used for heavier structural fabrication and repair where covered by the approved welding procedure.

Process Selection

The Project Manager should understand which process has been proposed and why, but should not instruct the welder to change from TIG to MIG, SMAW or another process simply for programme convenience.

If the proposed method appears inappropriate, the PM should challenge the technical basis and request confirmation from the welding supervisor, engineer or Class rather than taking over the specialist's responsibility.

MULTI-PASS & ONE-SIDED WELDING

Multi-Pass Welding

Structural butt welds in thicker plate normally require several weld passes rather than a single deposit.

A typical sequence may include:

• root pass

• hot pass where specified

• fill passes

• cap pass

The sequence is established by the welding procedure and is used to achieve the required penetration, fill the joint and control heat input and distortion.

One-Sided Full-Penetration Welding

During yacht refit, the reverse side of a structural plate is not always accessible.

Where permitted by the approved procedure, a full-penetration weld may be made from one side using a suitable temporary backing material, such as an approved ceramic backing strip.

The backing supports the root of the weld while the joint is completed from the accessible side.

This should form part of the approved welding procedure and should not be improvised simply because access to the reverse side is difficult.

Back Gouging

Back gouging is different.

Where both sides of a joint are accessible, one side may be welded first and the root then gouged or ground from the opposite side back to sound weld metal before completing the second-side weld.

PLATE REPLACEMENT & CLASS HOLD POINTS

Plate replacement during a yacht refit should be treated as a controlled structural repair with defined stages of inspection.

The exact inspection sequence depends on the repair, Classification Society requirements and agreed survey plan, but the Project Manager should establish the required hold points before cutting begins.

A hold point means that work should not progress beyond the agreed stage until the required inspection or approval has been completed.

1 — Define the Repair Area

The proposed repair boundary should be established from survey information, thickness measurements, visual inspection and the approved structural repair proposal.

The initial crop line should extend sufficiently into sound material to allow a satisfactory structural repair.

Before cutting, the PM should confirm:

• approved repair drawing or sketch

• plate grade and thickness

• structure behind the plate

• cables and pipework

• tanks and void spaces

• temporary support requirements

• hot-work controls

• Class attendance requirements

HOLD POINT 2 — REPLACEMENT PLATE FIT-UP

Once the repair boundary has been accepted, the replacement plate can be prepared and positioned.

Before final welding, the fit-up should be checked against the approved repair arrangement.

The inspection should consider:

• correct material grade

• correct plate thickness

• material traceability

• plate shape and forming

• edge preparation

• root gap

• alignment

• fairness with surrounding plating

• connection to frames and stiffeners

• temporary supports

• access for welding

Temporary Alignment

Strongbacks, dogs or other temporary attachments may be used to maintain the plate in the correct position during fit-up.

These attachments should be installed and subsequently removed in accordance with the approved shipyard or welding procedure.

The affected attachment areas should be dressed and inspected after removal where required.

HOLD POINT 3 — WELDING RELEASE

Once material, fit-up and joint preparation have been accepted, final welding may proceed in accordance with the approved WPS.

The welding specialist remains responsible for the welding technique and sequence.

The Project Manager should monitor that the agreed controls remain in place, including:

• correct welder

• correct WPS

• correct consumables

• preheat where required

• interpass-temperature control

• welding sequence

• temporary backing where applicable

• distortion control

• protection of adjacent systems

• continued hot-work and fire-watch controls

If the welder needs to depart materially from the approved repair or welding procedure, the PM should stop progression and obtain the required technical review rather than allowing an informal change.

HOLD POINT 4 — COMPLETED WELD & FINAL INSPECTION

Completion of the weld does not automatically mean that the structural repair has been accepted.

After suitable cooling and cleaning, the completed weld should first receive visual inspection.

The required NDT or tightness testing should then be carried out in accordance with the repair plan, Class requirements or agreed acceptance criteria.

Where defects are identified, the repair should remain open until the defect has been removed, repaired and re-examined satisfactorily.

PLATE REPLACEMENT CONTROL RECORD

The Project Manager should maintain a traceable repair record from initial defect through final acceptance.

This should include where applicable:

• original defect photographs

• thickness measurements

• initial NDT results

• repair drawing or sketch

• initial crop boundary

• final crop boundary

• photographs after crop-out

• Class comments or instructions

• replacement material certificate

• WPS reference

• welder qualification

• fit-up inspection

• welding records where required

• final visual inspection

• NDT report

• tightness-test result where applicable

• coating reinstatement

• final acceptance and close-out

A well-documented structural repair becomes part of the yacht's technical history and provides evidence for future surveys, refits, insurance matters and resale.

NON-DESTRUCTIVE TESTING — NDT

Non-Destructive Testing allows welds, materials and structural repairs to be examined without destroying or significantly damaging the component being inspected.

The Project Manager does not select or perform an NDT technique independently. The required method, examination extent and acceptance criteria should be established by the repair specification, Classification Society, welding engineer or other appropriate technical authority.

The PM should nevertheless understand what each method can and cannot demonstrate so that the correct inspection is incorporated into the repair programme.

NDT Control Principles

Before examination begins, the Project Manager should confirm:

• which welds or areas require examination

• which NDT method is specified

• extent or percentage of examination

• applicable acceptance criteria

• required surface preparation

• technician qualification or certification

• Class attendance or witnessing requirement

• access and safety requirements

• reporting format

• procedure for repair and re-examination if defects are identified

PAUT — Phased Array Ultrasonic Testing

Phased Array Ultrasonic Testing is an advanced ultrasonic technique using multiple elements within the probe to electronically control the sound beam.

It can provide detailed information about the location and orientation of internal weld discontinuities and may be specified for certain structural repairs or critical welds.

PAUT requires appropriately qualified personnel, approved procedures and suitable interpretation of the recorded data.

For the Project Manager, one advantage is that the examination can provide a traceable digital record of the inspected weld where the approved procedure requires this.

RT — Radiographic Testing

Radiographic Testing uses X-rays or gamma radiation to produce an image of the internal condition of a weld or component.

RT can be effective for identifying certain internal weld defects, but its use onboard or within an active shipyard requires careful planning because ionising radiation creates a significant safety hazard.

The Project Manager may need to coordinate:

• controlled exclusion zone

• restricted access

• warning signage

• communication with yacht and yard personnel

• timing outside normal work periods where required

• confirmation that the area is clear before exposure

The radiography specialist remains responsible for radiation safety and execution of the examination.

WHEN NDT IDENTIFIES A DEFECT

An unacceptable NDT indication should not simply be ground over, covered with additional weld metal or ignored because the repair appears satisfactory visually.

The defect should be assessed against the applicable acceptance criteria and an approved repair method established.

A typical sequence may be:

• identify and mark the defect location

• document the NDT result

• inform the responsible welding supervisor and PM

• inform Class where required

• remove the defective weld material back to sound metal

• prepare the repair area

• reweld using the applicable approved procedure

• allow appropriate cooling

• visually inspect the repaired area

• repeat the required NDT

• close the repair only after satisfactory re-examination

The original failed examination and the successful repair examination should remain part of the repair record rather than deleting evidence of the original defect.

TIGHTNESS & PRESSURE TESTING

NDT can demonstrate the condition of a weld, but a repair forming part of a tank, deck, shell or watertight boundary may also require a separate tightness or pressure test.

The required method depends on the structure, access, design pressure and applicable Class or repair requirements.

Typical Methods

• hose testing

• vacuum-box testing

• air-pressure or air-leak testing under an approved controlled procedure

• hydrostatic testing

• tank filling

• water-column testing where applicable

• other approved leak-detection methods

Vacuum-Box Testing

Vacuum-box testing can be particularly useful for examining accessible welded seams where the opposite side cannot easily be observed.

A leak-detection solution is applied to the test area and a transparent sealed box is placed over the weld. Reduced pressure inside the box can reveal leakage through the formation of bubbles.

Hydrostatic Testing

Where appropriate, a tank or system may be filled with water to establish the required test head or pressure.

The Project Manager should ensure that the structural and operational consequences of filling are considered before testing, including added weight, support condition, drainage and disposal of the test water.

Compressed-Air Testing

Compressed-air testing should only be carried out using an approved procedure with the appropriate safety controls.

Compressed gas stores significant energy and should not be treated in the same way as a simple water test.

The Project Manager should never request additional test pressure simply to make a leak easier to find.

NDT & TESTING — PROJECT MANAGER CONTROL

The Project Manager should be able to answer five questions before closing a structural repair:

1. What was inspected?

The exact weld, plate or repair location should be identifiable.

2. Which examination was required?

The NDT and tightness-test requirements should be known before final acceptance.

3. Who carried out the examination?

The technician and organisation should have the required competence and certification.

4. What was the result?

The report should state whether the examination met the applicable acceptance criteria.

5. Has the repair been formally closed?

Any defects should have been repaired, re-examined and accepted before the work package is considered complete.

PROJECT MANAGER COMPETENCY TEST

Scenario 1 — Welder Qualified, But for the Wrong Process

A subcontractor provides a welder qualification certificate before a structural repair. The certificate is valid, but the qualification covers a different welding process from the one proposed for the repair.

Question:

What should the Project Manager do?

A. Accept the certificate because the welder is generally qualified
B. Allow the work to begin if the welder has sufficient experience
C. Verify that the welder's qualification covers the actual process, material, thickness and welding position required for the repair
D. Ask the Captain to accept responsibility for the welder

Scenario 2 — Additional Corrosion After Cutting

Class has reviewed a proposed plate replacement. After the initial crop-out, the yard discovers significant additional corrosion behind the original repair boundary.

Question:

What should happen next?

A. Continue with the original replacement plate to protect the programme
B. Fill the additional wasted area with weld metal
C. Hold the repair and have the exposed structure and final crop boundary reassessed before continuing
D. Coat the additional corrosion and continue with fit-up

Scenario 3 — Reverse Side Is Inaccessible

A structural plate requires a full-penetration butt weld, but permanent outfitting prevents practical access to the reverse side of the joint.

Question:

What is the appropriate Project Manager response?

A. Tell the welder to complete a normal weld from one side and hope penetration is sufficient
B. Ask the welding specialist to establish whether an approved one-sided welding procedure with suitable temporary backing is applicable
C. Reduce the plate thickness to make welding easier
D. Accept a partial-penetration weld regardless of the approved repair requirement

Scenario 4 — Weld Looks Good but NDT Fails

A completed structural weld appears satisfactory during visual inspection, but ultrasonic testing identifies an unacceptable internal discontinuity.

Question:

What should the Project Manager do?

A. Accept the weld because the surface appearance is good
B. Ask the NDT technician to reduce the sensitivity of the test
C. Keep the repair open, remove the defective area as required, repair it using the approved procedure and repeat the required examination
D. Apply coating over the weld and monitor it during the next yard period

Scenario 5 — Watertight Repair

A welded repair forms part of a tank boundary. The weld has passed the specified NDT examination, and the subcontractor considers the repair complete.

Question:

Is the successful NDT result necessarily sufficient for final close-out?

A. Yes, NDT automatically proves watertightness
B. No. The approved repair may also require a separate tightness or pressure test before acceptance
C. Yes, provided the weld has been painted
D. No, but only because Class must always repeat the welding

MODULE COMPLETION

Before completing this module, the Project Manager should be able to:

• Understand the relationship between the repair drawing, material specification, WPS and welder qualification

• Verify that the welder is qualified for the required process, material, thickness and welding position

• Confirm that the applicable Welding Procedure Specification covers the actual repair

• Recognise the main marine welding processes including SMAW, MIG/MAG, TIG and FCAW

• Understand the purpose of root, fill and cap passes in multi-pass welding

• Recognise when an approved one-sided full-penetration welding procedure may be required

• Understand the difference between temporary backing and back gouging

• Coordinate structural crop-and-renew repairs through defined Class hold points where required

• Stop the repair when crop-out reveals additional deterioration

• Verify replacement material grade, thickness and traceability

• Coordinate replacement-plate fit-up and inspection before final welding

• Understand the purpose of strongbacks, dogs and temporary alignment attachments

• Recognise the importance of welding sequence, heat input and distortion control

• Maintain hot-work, fire-watch and adjacent-system protection throughout welding

• Understand the principal NDT methods used during structural repair

• Distinguish between VT, MT, PT, UT, RT and PAUT

• Understand the difference between ultrasonic thickness measurement and ultrasonic weld examination

• Confirm that NDT personnel and procedures meet the required qualification and approval requirements

• Keep a repair open when NDT identifies an unacceptable defect

• Coordinate repair and repeat examination of rejected welds

• Understand when a watertight or tank repair may require an additional tightness or pressure test

• Recognise the additional hazards associated with compressed-air testing

• Maintain Class, NDT, welding and material records as part of the permanent structural-repair file

• Close a repair only when workmanship, inspection, testing and documentation have all been accepted