Visual Testing (VT) Services

Visual testing is the oldest non-destructive method and still the one that finds the most defects. It is applied to almost every product as a quality assurance step, and the discontinuities it detects — those breaking the surface — are the ones most likely to propagate in service.

It is also the method most often done badly, because everyone assumes they can do it. Formal visual testing is a procedure with defined lighting, viewing distance, angle, surface preparation and acceptance criteria, carried out by a qualified inspector and recorded. That is a different activity from looking at a weld.

Techniques

• Direct visualThe eye within about 600 mm of the surface and at an angle not less than 30 degrees, with illumination at the level the standard specifies. Magnification and measuring aids applied as the acceptance criteria require.
• Remote visualBorescopes, videoscopes and camera systems where the surface cannot be reached — internal bores, vessel interiors, confined spaces and areas that would otherwise need scaffolding or entry.
• Translucent visualApplied to translucent materials where light transmission reveals internal condition.
• Weld measurementWeld gauges, fillet gauges and undercut gauges to verify profile, leg length, throat, reinforcement and undercut against the code limits.

What visual testing finds

• Surface cracking, in the weld, the heat-affected zone and the parent material
• Undercut, overlap and incorrect weld profile
• Surface porosity, blowholes and exposed slag
• Incomplete fill, excess reinforcement and incorrect leg length
• Arc strikes and weld spatter
• Misalignment, distortion and incorrect fit-up
• Corrosion, pitting, erosion and mechanical damage
• Incorrect or missing identification and marking
• Surface condition preventing valid examination by other methods

Before, during and after welding

The value of visual examination is largely determined by when it happens. Before welding, it verifies material identification, edge preparation, fit-up, root gap, alignment and cleanliness — defects caught here cost nothing to correct. During welding, it covers interpass cleaning, interpass profile and the condition of each run before it is buried by the next. After welding, it assesses the completed weld against the acceptance criteria.

Most visual inspection is commissioned only for the last of those three, which means the problems that were preventable are found when they are expensive.

Conditions and their verification

A visual examination is only valid under the conditions the standard specifies. Illumination at the surface is measured rather than judged, and the level required rises where fine detail matters. Viewing distance and angle are controlled. Surface condition must permit examination — scale, spatter, paint and dirt invalidate the result. Inspector vision is verified periodically, including near vision acuity and, where the criteria depend on it, colour perception. All of these are recorded, because a visual report without them cannot be relied upon.

Standards applied

• ASME Boiler and Pressure Vessel Code, Section V, Article 9 — visual examination, with acceptance to the relevant construction code section
• ISO 17637 — visual testing of fusion-welded joints
• AWS D1.1 for structural steel welding
• API 650, 653 and 510 where tank and vessel inspection codes govern
• Client, project and manufacturer specifications where these are more stringent

The gate for other methods

Visual examination precedes and conditions every other NDT method. A surface that fails visual acceptance cannot be validly examined by penetrant, magnetic particle or ultrasonic testing — contamination blocks penetrant, spatter produces false magnetic particle indications, and poor surface condition prevents ultrasonic coupling. Where visual examination identifies a surface that must be prepared before the specified method can proceed, we report it rather than perform a test whose result would not be meaningful.

Personnel and accreditation

Examination is carried out by inspectors qualified to ISO 9712 and ASNT SNT-TC-1A Level II, with CSWIP or AWS CWI welding inspection qualification where the work requires it, under Level III oversight. ITMAD is accredited to ISO/IEC 17020 as an inspection body, is an ADNOC approved inspection contractor, and is listed on the Abu Dhabi City Municipality register of Approved Third Party Inspection Bodies. Certificates are issued in the format required by the governing authority, including Dubai Municipality and the Dubai free zone authorities, and inspection is carried out across Dubai, Abu Dhabi, Sharjah and the northern Emirates.

What you receive

• A report identifying each item examined by weld number, part or drawing reference
• The technique applied, illumination level, viewing distance and any aids used
• Findings recorded with location, dimension and character, supported by photographs
• Measurements against the code limits where profile or dimension is the criterion
• Assessment against the acceptance criteria in your specification
• Inspector qualification and current vision verification record