ASNT Level II Ultrasonic Testing Procedure for Oil & Gas Inspection Services

Introduction

Ultrasonic Testing (UT) is a widely used nondestructive examination method in the oil and gas industry, employed to detect flaws, measure thickness, and evaluate material properties. The American Society for Nondestructive Testing (ASNT) Level II certification represents a proficient level of expertise allowing individuals to perform ultrasonic inspections and interpret results according to applicable codes and standards.

This document outlines the procedure for conducting ASNT Level II Ultrasonic Testing specifically tailored to oil and gas inspection services, where safety and reliability are paramount.

Scope and Applications

The ASNT Level II UT procedure applies primarily to inspection activities on components such as pipelines, pressure vessels, storage tanks, heat exchangers, and other critical equipment used in oil and gas operations. These inspections help identify cracks, corrosion, inclusions, laminations, and other discontinuities that could compromise structural integrity.

Ultrasonic Testing is extensively used for:

• Weld inspection and flaw detection
• Thickness and corrosion measurements
• Detection of laminations and inclusions
• Verification of bond quality
• Heat exchanger tube inspections

Personnel Qualifications and Responsibilities

Personnel performing ultrasonic testing must be certified in accordance with ASNT SNT-TC-1A or equivalent standards. An ASNT Level II technician is qualified to:

• Perform ultrasonic testing according to written procedures
• Set up and calibrate equipment for inspection activities
• Recognize and interpret reported indications
• Estimate size and location of discontinuities
• Document inspection results in compliance with client requirements

Level II technicians work under the direction of a Level III specialist, who maintains full responsibility for procedure development and final interpretation.

Equipment and Calibration

Primary equipment used includes ultrasonic flaw detectors, thickness gauges, transducers (probes), pulser/receivers, and calibration blocks. Proper calibration is critical and typically involves the following steps:

1. Equipment Setup: Verify the flaw detector functionality and battery status. Select appropriate probes for the inspection task (commonly 2 MHz to 10 MHz frequency).
2. Calibration Blocks: Use standardized calibration blocks, such as ASTM E 164 or API 1104 calibration blocks, with known reflectors for sensitivity settings.
3. Calibration of Sensitivity: Adjust instrument gain and sensitivity to detect the smallest relevant reflectors, typically set at 80% screen height on the reference reflector.
4. Velocity Calibration: Measure and verify the ultrasonic wave velocity in the material to improve sizing accuracy.
5. Verification of Calibration: Conduct calibration verification before and during inspections to maintain test reliability.

Inspection Procedure

The UT procedure for oil and gas inspection must be performed carefully to ensure detection of critical defects. The steps are as follows:

1. Preparation

• Review job specifications, codes (API, ASME, ASTM), and client requirements.
• Ensure test surface is clean, free of rust, paint, or other contaminants.
• Confirm accessibility and safety considerations (confined spaces, hazardous locations).

2. Equipment Setup and Calibration

Calibrate equipment as described in the previous section using relevant calibration standards and blocks.

3. Scanning Techniques

Depending on the inspection target, apply appropriate scanning approaches such as:

• Straight Beam Scanning: Used primarily for thickness gauging and surface-breaking discontinuities.
• Angle Beam Scanning: Commonly employed to inspect welds and detect planar defects oriented at angles to the surface, using wedges to direct the sound beam.
• Immersion and Water-Path Techniques: Utilized for more precise flaw detection in complex geometries.

4. Data Acquisition and Interpretation

Technicians must carefully interpret ultrasonic signals displayed as A-scans or B-scans, identifying signal amplitudes, time-of-flight, and echo patterns to locate and size defects.

Indications are evaluated against acceptance criteria defined by the governing code or client specifications.

5. Reporting

Prepare a detailed inspection report that includes:

• Equipment and calibration data
• Inspection method and scanning details
• Locations and types of detected indications
• Interpretation, evaluation, and acceptance status
• Signature of certified technician and supervisor

Common Challenges and Considerations

Ultrasonic testing in the oil and gas industry often presents challenges that require skilled evaluation to overcome:

Material Properties

Geometry variations and material heterogeneity (e.g., coarse grain steel) may cause ultrasonic noise and attenuate signals, requiring adjusted test parameters and probe selections.

Surface Condition

Surface roughness, coatings, and corrosion products can affect couplant flow and signal transmission, necessitating surface preparation or specialized couplants.

Access and Safety

Inspection in confined spaces or above-ground tanks requires strict adherence to safety protocols and might limit probe maneuverability, dictating method adaptation.

Interpretation of Indications

Discriminating between relevant defects and benign reflectors demands experience and continuous reference to standards like API 1104 (welds) and ASME Section V.

Standards and Codes

Successful ultrasonic inspection adheres to applicable standards for repeatability, accuracy, and safety, including but not limited to:

• ASNT SNT-TC-1A: Personnel qualification and certification guidelines
• ASTM E 164: Ultrasonic examination calibration standards
• API 1104: Welding of pipelines and related facilities standards
• ASME Boiler and Pressure Vessel Code, Section V: Nondestructive examination methods and procedures
• NACE SP0169: Control of external corrosion

Conclusion

ASNT Level II ultrasonic testing forms a cornerstone in the oil and gas inspection industry, enabling critical evaluations to ensure equipment integrity and operational safety. Proper training, precise calibration, methodical inspection procedures, and thorough interpretation are essential components underpinning effective UT practices.

Adherence to industry standards ensures reliability in flaw detection and structural assessment, ultimately contributing towards minimizing downtime, environmental risk, and improving asset lifetime in oil and gas facilities.