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

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

In the world of oil, gas, and chemical processing, maintaining pressure vessels and pipelines for safety is a top priority. Industry standards that have been built over the years such as API 510 Pressure Vessel Inspection Code: In-service Inspection, Rating, Repair, and Alteration [1] and API 570 Piping Inspection Code: In-service Inspection, Rating, Repair and Alteration of Piping Systems [2] to give certified inspectors the necessary tools to ensure pressure equipment can not only be safely run but also increase the remaining life of these critical systems. As technology evolves, so do the tools that we use to ensure this equipment can continue to operate safely. Advanced Non-Destructive Testing to Support API 510 Pressure Vessel and API 570 inspections has become a key enabler in this evolution, offering methods like acoustic emission testing (AET) and guided wave ultrasonic testing (GWUT) to optimize on-stream and other critical pressure vessels and piping inspection objectives. This makes the inspections faster, comprehensive, and more accurate to ensure the safety of all involved with these systems. This article discusses the application of acoustic emission testing (AET) and guided wave ultrasonic testing (GWUT) as they relate to API 510 pressure vessel and API 570 piping inspections.

Introduction to Pressure Vessel Inspection

API 510 applies to pressure vessels that are designed to operate at pressures greater than 15 psig and are constructed from metallic materials such as carbon steel, stainless steel, or alloy steels. The code covers vessels built in accordance with recognized design and fabrication standards, primarily the ASME Boiler and Pressure Vessel Code (Section VIII) [3], or equivalent construction codes. It governs the inspection, repair, alteration, and rerating of these vessels after they have been placed into service, ensuring their continued safe operation.

API 510 does not apply to vessels operating at 15 psig or lower, which are considered low-pressure or atmospheric tanks, nor to nonmetallic vessels such as those made from fiberglass-reinforced plastic (FRP). It also excludes boilers and piping systems, which are covered under other related codes such as API 573: Inspection of Fired Boilers and Heaters [4] 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 within industrial facilities.

API 572 [5] provides guidance on the inspection of 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 that may occur (such as corrosion, cracking, or embrittlement), and methods for detecting these issues, including 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. In essence, it serves as a companion document to API 510, offering detailed inspection practices to support effective implementation of that code.

According to API 572, acoustic emission testing (AET) is a nondestructive examination method used to detect active defects or structural changes in pressure vessels while they are under stress, typically 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. API 572 notes that 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 Acoustic Emission testing for pressure vessels in service. It is recognized that internal inspections are very effectively carried out using this advanced NDT testing methodology. Many owner-operators operating API-510 pressure vessels are opting for Acoustic emission testing in lieu of other forms of NDT due to the accuracy, safety, and speed at which AE testing provides.

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

The typical pressurization sequence begins by 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 (dwell period) long enough for acoustic emission activity to stabilize and be recorded. This allows the examiner 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 for 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, you can pinpoint specific locations on the vessels that release clustered acoustic emission while inferring the damage mechanism. By analyzing the waves, acoustic emission technicians can decipher the transient wave forms into what type of damage or defect is causing said acoustic emission. Decisions can then be made for further evaluations. This allows inspectors to catch problems early, 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 that are designed to operate at pressures greater than 15 psig and are constructed in accordance with recognized codes such as ASME B31.3 [6], B31.1 [7], or similar standards. 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 such as carbon steel, stainless steel, or alloys. 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 [7] serves as a companion document to API 570, providing practical guidance on how to implement 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

GWUT sends ultrasonic waves along the pipe's length, using the pipe’s geometry to guide the sound [9-10]. 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, shooting locations more than once further enhancing its ability and legitimacy of its results.

It also detects corrosion under insulation or buried pipes without needing to dig or strip coverings. A benefit of GWUT is its location accuracy. By using known pipeline geometric features such as welds, pipe supports, and other pipe geometry, the GWUT system calibrates for attenuation and sizing. GWUT supports API 570’s focus on thorough, efficient inspection, letting teams 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. The technology is also now code compliant and capable of being adopted into any facility or owner-operator’s inspection program. These NDT techniques help uncover hidden defects, boost safety, and support compliance. ultimately protecting assets and people alike.

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