Non-Intrusive Inspection

Sonomatic has pioneered the formal industry approach for Non-Intrusive Inspection (NII) and has led the implementation of this inspection strategy on sites around the world. Our clients include many of the major international operators and our involvement in the assessment, planning, inspection, and evaluation stages, covers over 1200 major process vessels worldwide. Sonomatic‘s ability to offer the full range of NII campaign services ensures that clients get the maximum benefit while retaining full confidence in equipment integrity.

We strive to provide the most comprehensive and safe inspection solutions for our clients.

Our experienced team combines advanced data science, and cutting-edge integrity engineering capabilities with our planning and development oNII. We are committed to providing quality solutions that meet the highest standards of safety and efficiency while at the same time having an auditable trail to assure the independence of each department. 

For pressure vessels, NII is increasingly being utilised as an alternative approach to the traditional Internal Visual Inspection (IVI), with some organisations aiming to eliminate vessel entry by 2026. 

In need of an Non-Intrusive inspection for your project? Get in touch with us today to learn more!

NII Offers Several Benefits, Including:
  • Reduced shutdown time.
  • Reduced personnel requirements.
  • Removal of hazards associated with confined space entry.
  • Removal of internal cleaning requirements.
  • No impact on vessel integrity.
  • Inspection data can be used for fitness for service (FFS) calculations.
  • More quantified and accurate results for both carbon steel and corrosion resistant materials.

Fully Integrated NII Service

As key authors of the NII recommended practice HOIS-RP-103, Sonomatic are global leaders in the implementation of NII. We are uniquely positioned to deliver fully integrated NII services including comprehensive inspection planning, assessments and evaluation services in addition to advanced NDT capabilities. Our Integrity Services department has a strong track record of successfully delivering pressure vessel NII for large scale offshore and onshore projects. 

Our Fully Integrated NII Services Offer Several Advantages:

Assessment and Work Scope

Each vessel is individually considered to determine whether NII is appropriate and, where applicable, a work scope will then be developed. As part of the work scope, a 3D model of the vessel will be created using Sonomatic’s SIMS software.

It is important to note that NII assessment is not a push button approach. While the recommended practice does stipulate a process to follow, experienced technical input and understanding is required. 

The Assessment Will Consider the Following:
  • Vessel information, including inspection history, operating conditions, and degradation threats.
  • Required inspection coverage.
  • Key inspection locations based on potential threats.
  • Appropriate inspection techniques.
  • Appropriate accuracy and probability of detection targets for the inspection.


Throughout the inspection phase of an NII, seamless interaction between the Integrity and Inspection team is vital to ensure an efficient and accurate inspection. Sonomatic offer a complete NII package from assessment to evaluation. During the inspection phase, any amendments to the inspection scope or follow-up on unexpected results is managed through efficient interaction between the relevant teams. 

Sonomatic’s Fully Integrated Approach to NII Ensures:
  • Expert review of work scopes.
  • Live 3D corrosion maps produced at collection.
  • Any substitute/additional areas or techniques can be included when required.


On completion of the inspection, the evaluation phase and analysis of the data is required as part of justification for deferment/replacement of IVI. The 3D models created at the work scope stage are auto-populated during the inspection and are used as a basis for the evaluation.

Evaluation Process:
  • Linking of inspection data to the 3D model.
  • Review conformance of the completed inspection against the work scope.
  • Analysis of inspection data.
  • Extrapolation of inspection data to estimate the thickness in any uninspected areas.
  • Make remaining life estimates based on limiting values and corrosion rates.


Increased Safety

Non-Intrusive Inspections are non-destructive, meaning that they are applied externally and do not require personnel to enter a vessel and avoid any safety concerns associated with vessel entry. Any results that necessitate repairs can be highlighted and repairs planned before a shutdown. This helps to maintain the structural integrity of your assets, ensuring that they remain safe and reliable. 

Cost Savings

Non-Intrusive Inspection methods are generally deployed while the vessel is online, meaning that shutdowns can be avoided or reduced. This increases production revenue making NII, overall, more cost-effective than intrusive methods. 

Higher Accuracy

Sonomatic uses advanced inspection technologies to provide the most accurate information about the condition of your assets. NII is quantitative and reproducible meaning that comparison of future, repeat, data is easy and will provide the most representative corrosion rates. 

Greater Efficiency

In most cases, NII can be performed while your assets are in use, meaning that they do not have to be taken offline for inspection. This helps to minimise downtime and increase overall efficiency. 

Frequently Asked Questions

Non-intrusive inspection (NII) is a safe and viable alternative to conventional internal visual inspection (IVI) of pressure vessels that, when executed effectively, offers an equivalent or improved level of assurance, provides significant cost benefits, and eliminates the need for Confined Space Entry (CSE). Sonomatic are key authors of the HOIS recommended practice for NII, published as HOIS-RP-103, which details how the NII process should be used.

NII is a process applied to pressure vessels. However, the term NII has often been, and continues to be, used within industry more generally to apply to inspections on various other components and to scenarios where the NII process summarised above has not been followed. It is important that the distinction between the NII process and the application of NDT is understood.

NII is a four stage process entailing:

  • Assessment
  • Work scope
  • Inspection
  • Evaluation

The assessment will consider various aspects of the vessel design such as operating parameters and risk based assessment (RBA) information to determine if NII is applicable. If NII is applicable, a work scope to determine representative locations will be developed and, following an inspection, an evaluation phase will assess the inspection to determine if the results enable the scheduled IVI to be replaced.

NII is not:

  • Any inspection that is performed without the need to open an equipment item.
  • An ad-hoc inspection that makes use of externally applied NDT techniques.

Yes, but it must be used with caution. The first in-service inspection (FISI) for a vessel is important as it is the first opportunity to confirm whether assumptions made for the integrity management of the vessel are correct, and whether the vessel is performing as expected. Internal Visual Inspection (IVI)  is the usual choice of inspection as visual inspection (coupled with NDT) can detect many types of degradation and can cover large areas of the vessel, provided they are accessible, i.e. IVI can often find unpredictable degradation. NDT inspection techniques used for NII must be chosen correctly for the type of degradation expected, and usually only sampling is used (unless a vessel is a Type C where 100% coverage is required). This means any NII for FISI must go above and beyond what would be required for a standard NII, Sonomatic has extensive experience of applying NII for FISI.

Occasionally, IVI is not possible for a vessel (e.g. a small vessel) or would be more damaging to a vessel (e.g. a heat exchanger that requires the bundle to be pulled), and NII might be the first choice for such cases.

Ideally vessels would have been built, manufactured, and commissioned with NII for FISI in mind. Sonomatic can help at the FEED stage of projects to ensure this happens.

Each vessel must be treated individually to determine whether it is suitable for NII, but usually NII would be suitable for most metallic pressure vessels and tanks that have an inspection history and have access to the external surface, e.g. insulation can be removed if present. This means tanks where the bottom is inaccessible are not likely to be suitable for NII, and double walled vessels will also not be suitable.

There are some techniques capable of inspecting through insulation (e.g. PEC), but the resolution and probability of detection capabilities of these techniques are not sufficient to provide enough confidence in the internal condition of the pressure retaining boundary to be able to fully replace IVI. It is best to remove insulation to do NII. This may mean that NII must be undertaken during a shutdown, but it can still bring significant cost savings, and safety improvements.

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