Table of Contents
- Overview of ASME BPVC Construction Code
- Ultrasonic Testing of Welds Shear Wave.
- Manual Phased Array E-scan and S-scan Inspection.
- E-scan and S-scan Inspection with Encoding Phased Array.
- Conclusion
Non-destructive inspection of welds complying with ASME pressure vessel and piping codes [1-3] is stipulated within these codes and further explained in ASME BPVC Section V. Ultrasonic testing can be used as an alternative method to radiographic testing to examine the welds in pressure vessels as long as the thickness of the thinner material under joining is 0.250 inches or more [4].
The minimum inspection of butt welds and branch weld connections in power piping codes is volumetric examination, which could be radiographic or ultrasonic examination. ASME Section V Article 4 is directly mentioned in the process piping code. The current article provides a summary of ultrasonic testing and phased array ultrasonic testing (PAUT) in fabrication and in-service inspection that is also discussed in other literature in the industry.
ASME Code Compliant Non-destructive Testing
Overview of ASME BPVC Construction Code
ASME BPVC Section VIII provides the specifications of the design and construction of pressure vessels. It is subdivided into Division 1 and Division 2, which have some distinctions regarding application, design philosophy, and safety concerns. An overview comparison of the two divisions is summarized below.
Table 1: General Comparison of ASME BPVC Division 1 and Division 2
ASME Section V is the code book that governs all NDT examination methods referenced here
worth reading before you go further
→ ASME Section V — What It Covers and Why It Matters
The disparities between these dichotomies are also applied on non-destruction examination demands. Division 1 typically requires visual and radiographic inspection based on the size of the vessel, the condition of service, and pressure ratings. Based on UW-51 (4) requirements of welding, ultrasonic testing can be applied in place of radiography where the thickness of the material thinned is not less than 0.25 inches.
UW-53, concerning ultrasonic inspection of welded joints, makes both conventional ultrasonic testing and phased array inspection systems and methods, such as phased array manual raster scanning, mandatory. At least, a 10% scan overlap is suggested. Although 45-degree angle is most often used, the real angle of inspection should be determined according to the weld geometry and material thickness so that the entire volumetric area gets covered by the weld and heat-affected zone (HAZ). Also, with the help of beam angles, it is suggested to utilize the beam angle between 0 and 60 degrees to detect transverse indications.
Division 1 Phased array ultrasonic testing with linear array probes is allowed under Division 1. Division 2 Phased array ultrasonic testing with linear array probes is allowed under Division 2. The following requirements are regulated by ASME Section V, Article 4 and Mandatory Appendices IV and V as mentioned in Section VIII Division 1. These appendices detail processes to undertake both manual raster scans and electronic scans, E-scans, and S-scans.
A linear array probe and a linear scan (E-scan) need to be differentiated. The probe configuration (a one-dimensional arrangement of elements) is termed a linear array, and a scanning method that is possible with such probes is termed an E-scan.
Ultrasonic Testing of Welds Shear Wave.
Ultrasonic examination of welds by conventional shear wave and phased array techniques in the field of ASME BPVC includes various aspects, such as qualified personnel, approved procedures, calibration equipment, reference blocks, and good reporting procedures. All these elements add more complexity that could be addressed in other sections.
As an example, a scan plan of a pipe, having a diameter of 30 inches and a wall thickness of 0.80 inches, with a single V-groove butt weld would be considered. The scan strategy should consider the various ultrasonic methods as per ASME Section V Division 1.
Indicatively, inspection at 45 degrees shear wave might not sufficiently cover the weld root in the first leg, especially in single V-groove welds. Conversely, shear waves with the angle of 60 degrees can enhance inspection of the roots but still leave some parts of the weld uncovered. It can be adjusted so as to fully cover both the weld and the HAZ.
Figure 1. Example 45 degree shear wave scan plan for 30” diameter 0.080” Single Vee Butt Weld showing limited roof coverage in the first leg.
Figure 2. Example 60 degree shear wave scan plan for 30” diameter 0.080” single vee butt weld showing root coverage in first leg.
Manual Phased Array E-scan and S-scan Inspection.
ASME BPVC Section V Article 4 Mandatory Appendix IV describes in brief manual phased array ultrasonic testing procedures with E-scans and S-scans. This appendix gives a brief outline and is based on ASTM E2700-20 [5] to elaborate further.
ASTM E2700-20 contains examples of phased array inspections of multiple weld styles, including thin and thick butt welds, T-joints, and corner welds, scanning on a variety of surfaces.
The standard gives guidelines on how to choose the correct shear wave angles and offset of the index to make sure that all volumes of the welds and the areas affected by heat are fully inspected. Several scan groups or different index offsets might be necessary depending on probe choice and wedge geometry.
An example can be a 45-degree E-scan is not always able to fully scan the weld root and a 60-degree scan is better, although it still may not be sufficient in some areas. Further adjustment of the index offset will enable full inspection of the weld and HAZ. It is also a standard to carry out the scans on both sides of the weld to have a complete assessment.
Figure 3. Example 45-degree PAUT E-scan plan for 30” diameter 0.080” single vee butt weld showing poor coverage in first leg.
Figure 4. Example 60-degree PAUT E-scan plan for 30” diameter 0.080” single vee butt weld showing minimal coverage in first leg.
E-scan and S-scan Inspection with Encoding Phased Array.
Encoded phased array ultrasonic testing is also covered by ASME BPVC Section V Article 4 Mandatory Appendix IV although it is not mentioned in the title. Like manual inspection, the appendix describes general procedural requirements, but does not specifically mention ASTM E2700-20.
In the case of automated or semi-automated scanning systems having positional encoders, there are parameters that need to be controlled. These are keeping encoder accuracy to within 1%, uniform motion of the probe with proper guidance systems, and setting limits to scan resolution.
One example is that the system must obtain at least three data points in the shortest detectable flaw length, and the highest scan resolution should not be more than 2 mm (0.080 inches).
The encoded S-scan strategies indicate that a sectorial scan range between 45° to 70° can be used to cover the weld root in the first leg. By changing the index position of a range of about -17 mm to -30 mm and in effect, inspection of the weld and HAZ is complete.
The code also requires inspection to be done on the other side of the weld either with a different probe or a second scan pass. This can be optimized further by the proper choice of probes, wedges, aperture sizes and the utilization of multiple scan groups to enhance coverage on the first and second legs.
Not familiar with how Phased Array Ultrasonic Testing actually works before diving into ASME scan requirements?
→ Phased Array Ultrasonic Testing — A Complete Guide
Figure 5. Example 45 – 70 PAUT E-scan plan for 30” diameter 0.080” single vee butt weld showing root and weld volume coverage in the first and second legs.
Figure 6: Example 45 – 70 PAUT E-scan plan for 30” diameter 0.080” single vee butt weld showing full weld coverage.
Conclusion
ASME-compliant ultrasonic testing of welds (be it in conventional shear wave testing or phased array testing), necessitates a thorough knowledge of pressure vessel construction codes, non-destructive testing standards, piping standards, and ASTM E2700 standards.
Compliance also implies the correct methods of inspections as well as the compliance with the requirements regarding the qualification of the personnel, calibration of equipment, references, procedures and reporting standards. Construction codes define these aspects and elaborate on non-destructive testing standards.
This article presents significant areas of Section IX of ASME BPVC Division 1 (2023) and Section V of ASME Non-destructive Examination (2023) and ASTM E2700-20, and is in line with the larger industry discussions about ultrasonic weld inspection as part of the ASME Boiler and Pressure Vessel Code.
References
1. ASME Boiler and Pressure Vessel Code, Section V Non-destructive Examination, 2023
2. ASME B31.1 Power Piping, 2023
3. ASME B31.3 Process Piping, 2023
4. ASME BPVC Rules for Construction of Pressure Vessels Section VIII Division 1, 2023
5. ASTM E2700-20 Standard Practice for Contact Ultrasonic Testing of Welds Using Phased Arrays
Author:
1. Thomas R. Hay, Ph.D., P.E., President (TechKnowServ)
