Aplicação

Application Notes

Detection of Hydrogen-Induced Cracking (HIC)

General Description of the Application

Hydrogen-induced cracking (HIC) can occur in susceptible steels exposed to aqueous environments containing hydrogen sulphides. It is a form of hydrogen-related cracking and can have two distinct morphologies:

1. The first type is commonly referred to as hydrogen-induced cracking (HIC) and can occur where little or no applied or residual tensile stress exists. It is manifested as blisters or blister cracks oriented parallel to the plate surface.

2. The second type produces an array of blister cracks linked together in the through thickness direction by transgranular cleavage cracks. The latter type of cracking is referred to as stress-oriented hydrogen-induced cracking (SOHIC). SOHIC can have a greater effect on serviceability than HIC because it effectively reduces load carrying capabilities to a greater degree.

The inspection requires characterization of the defect areas to differentiate between spot inclusions, laminations, and different stages of hydrogen-induced cracking (HIC).

The benefit of electronic angle sweeping (S-scans) provided by the OmniScan™ allows simultaneous scanning from −30 to +30 degrees. The imaging from this scanning technique allows the user to distinguish between spot indications and interconnected defects.

Typical Inspection Requirements

Heavy wall carbon steel vessels
Thickness ranges of 10 mm (0.375 in.) to 150 mm (5.9 in.)

Advantages of Phased-Array Technique

Imaging giving easy interpretation of links between defects
Setup time between inspections decreased due to portability

Type of Defects

Spot inclusions
Laminations
Side step cracking (SOHIC)

Description of the Solution

Manual inspection using an OmniScan™ and phased-array probe
Inspection setup using a −30- to +30-degree LW refracted angle sectorial scan
Real-time display of A-scan and S-scan data
Capable of storing display screen captures or full data file for offline analysis on computer-based software (TomoView™)

Equipment Required

OmniScan™ PA Weld package
5-MHz 16-element phased-array probe
TomoView® software for advanced analysis

Inspection Method
A 0-degree raster scan is used to find the area that has laminations. Then the phased array probe using the −30- to +30-degree S-scan setup is manually scanned over on the areas where defects have been found to determine if there is a link between those defects.

Screen shots and reports of the defect can be immediately created for later printouts.

Products used for this application

OmniScan MX

The OmniScan MX is an advanced, multi-technology flaw detector. It offers a high acquisition rate and powerful software features-in a portable, modular instrument to efficiently perform manual and automated inspections. Available with PA and conventional UT modules, and conventional EC and ECA modules.

OmniScan MX2NEW

The OmniScan MX2 phased array flaw detector with touch screen interface offers increased testing efficiencies and powerful software features, ensuring superior manual and advanced AUT application performance with fast setups, test cycles, and reporting. It is compatible with all existing phased array modules.

TomoView Software

TomoView is a PC-based software for data acquisition and visualization of ultrasonic signals.