Advanced Non-Destructive Testing to Support API 510 Pressure Vessel and API 570

In the oil, gas, and chemical processing industries, safety is paramount. Maintaining pressure vessels and pipelines is crucial for ensuring operational safety. Industry standards, such as the API 510 Pressure Vessel Inspection Code and the API 570 Piping Inspection Code, provide certified inspectors with the necessary tools to ensure that pressure equipment operates safely. These standards also help extend the lifespan of critical systems.

As technology advances, so do the tools we use for inspections. Advanced Non-Destructive Testing (NDT) methods, including Acoustic Emission Testing (AET) and Guided Wave Ultrasonic Testing (GWUT), are becoming essential for optimizing inspections of pressure vessels and piping systems. These methods enhance the speed, comprehensiveness, and accuracy of inspections, ensuring the safety of all personnel involved. This article explores the applications of AET and GWUT in relation to API 510 and API 570 inspections.

Understanding Pressure Vessel Inspection

API 510 applies to pressure vessels designed to operate at pressures exceeding 15 psig. These vessels are typically constructed from metallic materials, including carbon steel, stainless steel, or alloy steels. The code governs the inspection, repair, alteration, and rerating of these vessels after they are in service, ensuring their continued safe operation.

It's important to note that API 510 does not apply to vessels operating at 15 psig or lower. Such vessels are classified as low-pressure or atmospheric tanks. Additionally, nonmetallic vessels, such as those made from fiberglass-reinforced plastic (FRP), are excluded. Boilers and piping systems fall under other codes, like API 573 for fired equipment and API 570 for piping inspection. In summary, API 510 establishes the requirements for maintaining the integrity and safety of metallic pressure vessels operating above 15 psig.

API 572 provides guidance on inspecting pressure vessels covered under API 510. It outlines the principles, practices, and techniques used to evaluate the condition of vessels during both internal and external inspections. The standard explains inspection objectives, types of deterioration (such as corrosion, cracking, or embrittlement), and methods for detecting these issues. These methods include visual, nondestructive, and pressure testing techniques. API 572 also addresses inspection frequency, recordkeeping, and the role of inspectors in ensuring continued vessel integrity and safe operation. Essentially, it serves as a companion document to API 510, offering detailed inspection practices to support effective implementation of that code.

Acoustic Emission Testing (AET)

According to API 572, AET is a nondestructive examination method used to detect active defects or structural changes in pressure vessels while they are under stress. This typically occurs during hydrostatic or pneumatic testing. The technique involves monitoring transient elastic waves, or "acoustic emissions," generated by the rapid release of energy from localized sources within the material, such as crack growth, corrosion activity, or leakage. Specialized sensors placed on the vessel's surface capture these signals, which are then analyzed to identify areas of potential concern.

AET is particularly useful for screening large vessels or complex geometries to locate active flaws that might not be easily detected through conventional inspection methods. However, it should be supplemented by follow-up examinations, such as ultrasonic or radiographic testing, to confirm and characterize any indications found.

Acoustic Emission Testing in Accordance with ASME Sec V Article 12

API 510 references ASME Sec V Article 12 specifically for these tests. This article covers Acoustic Emission Examination of Metallic Vessels During Pressure Testing. API 572: Inspection Practices for Pressure Vessels is also referenced by API 510 and provides guidelines for the best-case usage of AET for pressure vessels in service. Many owner-operators of API-510 pressure vessels are opting for AET due to its accuracy, safety, and speed.

AET detects fatigue cracks, stress corrosion cracks, and corrosion activity during vessel pressurization. It works by listening to the sounds of tiny cracks or corrosion occurring inside vessels under stress. ASME Section V Article 12 outlines the pressurization sequence to induce these acoustic emission sources. Fatigue cracks, stress corrosion cracks, and corrosion activity release acoustic emissions in the form of elastic waves. High-frequency acoustic emission sensors are strategically placed to triangulate the acoustic emissions using hit arrival times for accurate source location.

The typical pressurization sequence begins with gradually increasing pressure in incremental steps, usually to predetermined percentages of the vessel's test pressure—such as 30%, 50%, 70%, 90%, and 100%. At each increment, the pressure is held long enough for acoustic emission activity to stabilize and be recorded. This allows examiners to distinguish between emission signals caused by new defects and those due to structural settling or equipment noise. Once the full test pressure is reached, it is held for a specified period to monitor any continuing acoustic activity that could indicate crack propagation or other active flaws.

Figure 1-1: ASME Section V Article 12 example of pressure vessel test stressing sequence.

With this information, inspectors can pinpoint specific locations on the vessels that release clustered acoustic emissions while inferring the damage mechanism. By analyzing the waves, acoustic emission technicians can decipher the transient waveforms to identify the type of damage or defect causing the emissions. This allows for timely decisions regarding further evaluations, helping to maintain safe operations and avert costly failures.

Figure 1-2: 3D Representation of Acoustic Emission being carried out on a pressure vessel and a 2D layout of clustering of AE hits.

Introduction to Piping Inspection

API 570 applies to metallic piping systems designed to operate at pressures greater than 15 psig. These systems are constructed in accordance with recognized codes such as ASME B31.3 or B31.1. The code governs the inspection, repair, alteration, and rerating of in-service piping systems used in the petroleum, chemical, and related industries. It covers process piping of any diameter, including small-bore and large-diameter lines, if they are pressurized beyond 15 psig and constructed from metal materials.

API 570 does not apply to nonmetallic piping (such as FRP or plastic), buried pipelines regulated by the U.S. Department of Transportation, or piping systems operating at or near atmospheric pressure. In summary, API 570 establishes requirements to ensure the mechanical integrity and safe operation of metallic pressure piping systems operating above 15 psig in industrial service.

API 574 serves as a companion document to API 570, providing practical guidance on implementing the inspection requirements outlined in API 570 for in-service piping systems. While API 570 establishes the rules and responsibilities for inspection, repair, and alteration, API 574 focuses on the methods and techniques used to perform those inspections effectively. It offers detailed recommendations on visual examination practices, common damage mechanisms, corrosion monitoring, thickness measurement, and the use of inspection tools and records. API 574 supports the intent of API 570 by explaining how to apply its requirements in the field, ensuring consistent and thorough inspection of metallic piping systems operating above 15 psig.

Guided Wave Ultrasonic Testing of Pipelines

Guided Wave Ultrasonic Testing (GWUT) sends ultrasonic waves along the pipe's length, using the pipe's geometry to guide the sound. GWUT probes transmit and receive signals, revealing wall thinning, corrosion, and defects far from the inspection site. This technique is excellent for long-range screening, allowing hundreds of feet to be inspected from a single spot. GWUT is quick and non-intrusive, minimizing downtime and working in hard-to-reach areas. It can also be adapted for large windings and multiple pipe sections, enhancing its effectiveness.

GWUT detects corrosion under insulation or buried pipes without the need for digging or stripping coverings. One of the key benefits of GWUT is its location accuracy. By using known pipeline geometric features such as welds and pipe supports, the GWUT system calibrates for attenuation and sizing. GWUT supports API 570's focus on thorough, efficient inspection, allowing teams to prioritize repairs and direct more detailed inspections where they're needed most.

Figure 1-3: 100-foot section with inspection results showing defects and different geometry structures throughout the pipeline.

By adopting Acoustic Emission Testing with API 510 and Guided Wave Ultrasonic Testing with API 570, facilities gain a smarter approach to equipment monitoring. These NDT techniques help uncover hidden defects, boost safety, and support compliance, ultimately protecting assets and people alike.

Conclusion

In conclusion, the integration of advanced non-destructive testing methods like AET and GWUT into the inspection processes for pressure vessels and piping systems is essential for maintaining safety and compliance in the oil, gas, and chemical processing industries. These techniques not only enhance the accuracy and efficiency of inspections but also contribute significantly to the longevity of critical infrastructure.

References

1. API 510: Pressure Vessel Inspection Code – In-Service Inspection, Rating, Repair, and Alteration

2. API 570: Piping Inspection Code – In-Service Inspection, Rating, Repair, and Alteration of Piping Systems

3. ASME Boiler and Pressure Vessel Code (Section VIII)

4. API 573: Inspection of Fired Boilers and Heaters

5. API 572: Inspection Practices for Pressure Vessels

6. ASME B31.3: Code for Pressure Piping

7. ASME B31.1: Code for Power Piping

8. API 574: Inspection Practices for Piping System Components

9. ASTM E2929-18: Standard Practice for Guided Wave Testing of Above Ground Steel Piping with Magnetostrictive Transduction

10. ASTM E2775-16: Standard Practice for Guided Wave Testing of Above Ground Steel Pipework Using Piezoelectric Effect Transduction