Stud Bolt Inspection by Advanced ultrasonic testing

Stud bolt inspection by advanced ultrasonic method

Introduction

In the petrochemical industry, stud bolts are essential fasteners that secure components and maintain the structural integrity of facilities, but the continuous stress they endure can lead to degradation and pose significant safety risks. Traditional inspection methods, often requiring equipment shutdowns, may not effectively detect fine cracks within complex thread forms, potentially leading to catastrophic accidents, injuries, and extensive equipment damage. These limitations result in costly production downtime and financial losses, highlighting the need for advanced inspection techniques to ensure the safety and reliability of critical equipment.

a stud bolt crack and subsequent detachment from the equipment resulted in a plant shutdown for inspection, repair and maintenance

Technical detail:

Stud bolt inspections are customarily performed during scheduled shutdowns or turnarounds. These maintenance intervals are necessary to decommission equipment, facilitating the extraction of stud bolts for examination using non-destructive testing (NDT) techniques.

Visual Inspection: Primary assessment to identify visible surface defects.

Liquid Penetrant Testing (PT) or Magnetic Particle Testing (MT): Methods employed to detect and characterize surface and near-surface discontinuities.

Fine cracks within the complex thread forms of stud bolts present a significant challenge for detection and sizing using conventional NDT methodologies, particularly those that rely on penetrant removal for effective inspection.

In such situations, advanced ultrasonic testing methods, such as Phased Array Ultrasonic Testing (PAUT) and the Total Focusing Method (TFM), offer the most effective means for detection, crack depth measurement, and suitability for on-stream inspection.

Phased array ultrasonic testing (PAUT) is an advanced method of ultrasonic testing (UT) that uses a set of ultrasonic testing probes made up of numerous small elements. Each of these is pulsed individually with computer-calculated timing to create the phased aspect of the process, while the array refers to the multiple elements within PAUT system

Elements are pulsed in groups with precalculated time delays for each element.

Full Matrix Capture (FMC) is a specialized data acquisition process employed with ultrasonic array probes. In FMC, each element of the array is sequentially used as a transmitter, while all elements function as receivers for every transmitted pulse.

The Total Focusing Method (TFM) is a computational analysis technique that utilizes the extensive data obtained through the FMC process.  TFM allows for precise focusing on specific areas of interest within the inspected material.

TFM scan shows the stud bolt is in good condition

TFM scan shows a crack indication (defect 1) at a distance of 68.5 mm from the

reference point, and depth of crack

TFM scan shows a crack indication (defect 2) at a distance of 87 mm from the reference point, with a high-amplitude signal in the A-scan. The T-scan provides easily understandable information about the defect's characteristics."

On-Field Practice (On-stream Inspection)

Our field experiments demonstrate the efficacy of our methodologies and advanced technologies in accurately identifying both sound and damaged stud bolts. The images above illustrate a sound stud bolt and one with cracking, as indicated in S-scan mode. The superimposed 3D stud bolt image precisely locates the position of the crack. Following the ultrasonic inspection, our team removed the suspect stud bolt and confirmed the presence of the crack using liquid penetrant testing, validating the findings of our advanced ultrasonic inspection method.

Key benefits:

Detection of Internal Defects: Ultrasonic testing can identify cracks, corrosion, and other flaws located within the stud bolt material, not just those visible on the surface.

Sizing and Location: Advanced techniques like PAUT and TFM allow for accurate measurement of crack size and precise determination of their location within the stud bolt.

On-Stream Inspection: Ultrasonic methods can often be applied without taking equipment offline and without the need to remove the stud bolt, minimizing disruptions to operations.

Versatility: Ultrasonic testing can be adapted to inspect various stud bolt shapes, sizes, and materials.

Environmental Friendliness: As a non-destructive testing method, ultrasonic testing avoids the need for destructive sampling or the generation of hazardous waste, contributing to a more sustainable inspection process.