PAUT vs Radiographic Testing

July 24, 2026

PAUT vs Radiographic Testing for Weld Inspection

Phased Array Ultrasonic Testing (PAUT) and Radiographic Testing (RT) are advanced nondestructive testing methods used for the volumetric examination of welds and industrial components.

PAUT uses high-frequency sound waves to identify discontinuities inside a component. Radiographic testing uses X-rays or gamma rays to produce an image based on differences in material thickness and radiation absorption.

Both methods have important industrial applications. However, they differ in their sensitivity to defect orientation, safety requirements, inspection speed, sizing capability, access requirements and presentation of results.

The selection between PAUT and radiography must be based on the applicable construction code, component geometry, material, expected defect types and client specifications.

What Is PAUT?

PAUT uses a multi-element ultrasonic probe in which individual elements are activated using controlled time delays.

This allows the system to:

➤ Electronically steer the ultrasonic beam

➤ Generate multiple inspection angles

➤ Focus at selected depths

➤ Cover different parts of the weld

➤ Display cross-sectional scan images

➤ Record complete inspection data

➤ Locate and size discontinuities

PAUT can be performed manually or with an encoded scanner. Encoded PAUT records the position of the probe together with the ultrasonic data, providing a traceable inspection record.

What Is Radiographic Testing?

Radiographic testing passes X-rays or gamma rays through the inspected component. A film or digital detector is placed on the opposite side to record the radiation transmitted through the material.

Variations in material thickness or density create differences in the radiographic image.

Radiography may use:

➤ X-ray equipment

➤ Gamma-ray sources

➤ Industrial radiographic film

➤ Computed radiography

➤ Digital detector arrays

➤ Real-time radiography systems

Radiographic testing is widely used for welds, castings and manufactured components.

PAUT and Radiography Comparison

Inspection factor	PAUT	Radiographic testing
Energy used	High-frequency sound waves	X-rays or gamma radiation
Radiation hazard	No ionising radiation	Uses ionising radiation
Typical access	Often possible from one surface	Generally requires access to both sides
Defect sensitivity	Particularly effective for suitably oriented planar defects	Generally effective for volumetric defects and thickness variations
Through-wall sizing	Possible with an approved sizing technique	Usually limited from a single radiographic image
Defect depth	Can provide depth and sound-path information	Depth is difficult to determine from a single exposure
Inspection result	Ultrasonic scans and digital data	Two-dimensional radiographic image
Work interruption	Normally minimal	Radiation exclusion zone may interrupt nearby work
Consumables	Couplant and normal inspection accessories	Film, chemicals or digital imaging accessories
Inspection speed	Rapid after completing setup and calibration	Exposure and image-processing time may be required
Data availability	Often available immediately	Depends on film or digital processing method
Repeatability	High with encoded scanning	Exposure conditions must be reproduced
Material thickness	Suitable for a broad range, subject to technique	Exposure time increases with material thickness
Surface preparation	Requires suitable scanning surface and coupling	Less dependent on scanning-surface smoothness
Defect orientation	Beam direction strongly affects detection	Defect orientation relative to radiation direction affects visibility

Defect Detection Capability

PAUT Detection

PAUT can detect discontinuities such as:

➤ Lack of sidewall fusion

➤ Lack of root fusion

➤ Cracks

➤ Incomplete penetration

➤ Slag inclusions

➤ Laminations

➤ Corrosion

➤ Service-induced cracking

PAUT is particularly effective for planar discontinuities when the ultrasonic beam is directed appropriately toward the defect.

Radiographic Detection

Radiography is generally effective for discontinuities that produce a measurable change in material thickness or density, including:

➤ Porosity

➤ Slag inclusions

➤ Volumetric cavities

➤ Incomplete penetration

➤ Burn-through

➤ Certain cracks and lack-of-fusion defects

Tight planar discontinuities may be difficult to detect radiographically when their orientation is not aligned suitably with the radiation beam.

Defect Location and Sizing

PAUT

PAUT can provide information about:

➤ Indication depth

➤ Sound-path distance

➤ Position relative to the weld centreline

➤ Indication length

➤ Through-wall location

➤ Estimated through-wall height

Accurate sizing depends on the selected technique, calibration, defect orientation, signal quality and operator competency.

Radiography

A radiograph provides a two-dimensional projection of a three-dimensional component. It can show the position and approximate length of an indication on the image.

However, determining the exact depth and through-wall height of a defect from a single radiographic image is generally difficult. Additional exposure angles may be required for improved location information.

Safety Requirements

PAUT Safety

PAUT does not use ionising radiation. Therefore:

➤ A radiation exclusion zone is not required

➤ Nearby work can normally continue

➤ Inspection can be performed during active fabrication

➤ There is no radioactive source handling

➤ Source transportation and storage are not required

Normal site safety controls, electrical safety, access control and working-at-height requirements still apply.

Radiographic Safety

Radiographic testing requires strict radiation-safety controls, including:

➤ Radiation exclusion zones

➤ Warning signs and barricades

➤ Qualified radiography personnel

➤ Radiation monitoring

➤ Controlled source handling

➤ Approved source storage

➤ Transportation compliance

➤ Emergency arrangements

These requirements can affect inspection schedules in operating plants, fabrication facilities and congested work areas.

Inspection Access

PAUT can often be performed from one side of a component. The probe and wedge must have sufficient space to scan beside the weld.

Radiography usually requires:

➤ Access for positioning the radiation source

➤ Access to place film or a detector on the opposite side

➤ Adequate source-to-detector distance

➤ Space for radiation barriers

➤ Control of the surrounding work area

For pipes, vessels or components with restricted rear-side access, PAUT may be more practical.

Inspection Speed and Productivity

PAUT can provide immediate results once the equipment is configured and calibrated. Encoded scanners can improve productivity for repeated weld configurations.

Radiographic inspection time can be influenced by:

➤ Material thickness

➤ Radiation source strength

➤ Exposure duration

➤ Film placement

➤ Film processing

➤ Image quality verification

➤ Radiation-zone establishment

➤Retakes due to image-quality issues

Digital radiography may reduce image-processing time, but radiation-safety controls remain necessary.

Inspection Records

PAUT Records

Encoded PAUT data may include:

➤ Complete ultrasonic scan files

➤ Weld identification

➤ Probe position

➤ Scan length

➤ Calibration information

➤ Sectorial scan images

➤ Indication locations

➤ Analysis and evaluation results

The data can be reviewed after inspection and compared with future examinations.

Radiographic Records

Radiographic records may include:

➤ Film or digital images

➤ Weld identification

➤ Image-quality indicators

➤ Exposure parameters

➤ Location markers

➤ Interpretation reports

Radiographs provide an easily recognizable image, but they represent a two-dimensional projection through the component.

Advantages of PAUT Over Radiography

PAUT may offer the following benefits:

➤ No ionising radiation

➤ No radiation exclusion zone

➤ Inspection possible from one surface

➤ Immediate inspection results

➤ Detailed defect-depth information

➤ Through-wall sizing capability

➤ High sensitivity to suitably oriented planar defects

➤ Digital data storage

➤ Encoded and repeatable inspections

➤ Reduced disruption to surrounding activities

➤ No radiographic film or chemical processing

➤ Suitable for thick components

Advantages of Radiography

Radiography remains valuable because it can provide:

➤ A permanent image of the inspected area

➤ Good detection of volumetric discontinuities

➤ Clear identification of porosity and slag patterns

➤ Inspection of some complex manufactured components

➤ Less dependence on ultrasonic coupling

➤ Results that are visually familiar to many clients

➤ Examination of certain geometries that are difficult to scan ultrasonically

Limitations of PAUT

PAUT performance may be affected by:

➤ Rough scanning surfaces

➤ Poor ultrasonic coupling

➤ Complex component geometry

➤ Restricted probe access

➤ Coarse-grained materials

➤ High material attenuation

➤ Inaccurate weld dimensions

➤ Unfavourable defect orientation

➤ Incorrect scan-plan design

➤ Inappropriate probe or wedge selection

PAUT requires qualified personnel, validated procedures and suitable calibration blocks.

Limitations of Radiography

Radiographic limitations may include:

➤ Ionising-radiation hazards

➤ Requirement for controlled exclusion zones

➤ Access to both sides of the component

➤ Operational disruption

➤ Limited defect-depth information

➤ Limited through-wall sizing capability

➤ Reduced sensitivity to unfavourably oriented planar defects

➤ Longer exposure times for thick materials

➤ Source handling and transportation requirements

➤ Film processing and storage requirements

Can PAUT Replace Radiography?

PAUT can replace radiography in some applications, but the substitution is not automatic.

Before replacing RT with PAUT, the following must be confirmed:

➤ Construction code permits the alternative method

➤ Client approves the proposed inspection technique

➤ PAUT procedure is qualified

➤ Scan plan demonstrates adequate coverage

➤ Calibration block is suitable

➤ Personnel qualifications meet project requirements

➤ Acceptance criteria are clearly established

➤ Demonstration or performance qualification is completed where required

The engineering or inspection authority should approve any change from the originally specified NDT method.

PAUT, TOFD and Radiography

For critical welds, PAUT may be combined with Time of Flight Diffraction (TOFD).

PAUT provides directional coverage and helps detect defects at different orientations. TOFD can provide reliable through-wall sizing for suitable components. This combination can offer comprehensive weld examination with permanent digital records.

Radiography may still be retained for specific welds or defect types where it provides a technical advantage.

Selecting the Correct NDT Method

The inspection method should be selected after reviewing:

➤ Applicable construction code

➤ Material specification

➤ Component diameter and thickness

➤ Weld preparation

➤ Expected defect type

➤ Defect orientation

➤ Access conditions

➤ Surface condition

➤ Radiation-safety restrictions

➤ Inspection schedule

➤ Data-recording requirements

➤ Acceptance criteria

In some applications, using complementary methods provides greater inspection confidence than relying on one technique alone.

Our PAUT and Advanced NDT Services

Integrity & Advanced Inspection Solutions India Private Limited provides:

➤ PAUT weld inspection

➤ Encoded PAUT scanning

➤ PAUT and TOFD combined inspection

➤ Conventional ultrasonic testing

➤ Pipeline girth-weld inspection

➤ Pressure-vessel weld inspection

➤ Small-bore piping inspection

➤ Corrosion mapping

➤ Procedure and scan-plan preparation

➤ Calibration-block development

➤ On-site analysis and reporting

➤ Inspection feasibility studies

Request a PAUT Feasibility Assessment

Clients planning to replace radiography with PAUT should share:

➤ Component drawings

➤ Weld details