By the PICA Corp Engineering Team  |  Updated September 2026  |  Est. reading time: 9 min

Every pipeline inspection vendor says its technology is accurate. Very few can point to a test where somebody else decided what accurate meant.

That is the value of blind verification testing. Defects of known size and location are built into test pipe. The inspection vendor is told nothing about them. The vendor runs its tool, submits its findings, and an independent party scores the results against the record. There is no opportunity to tune the analysis toward an answer you already know.

In 2024, Simpson Gumpertz & Heger Inc. (SGH) ran exactly that kind of comparison on AWWA C303 bar-wrapped pipe, testing two electromagnetic technologies across two vendors. PICA was one of them. This article covers what the study did, what it found, and the part most summaries leave out: where the technology reached its limits and why.

---

What blind verification testing actually proves

Most inspection accuracy claims come from the vendor that performed the inspection. Even honest ones are hard to compare, because every vendor reports against a different defect set, on different pipe, under different conditions.

Blind testing removes the vendor’s information advantage. Somebody else builds the defects, records their exact dimensions and positions, and keeps that record sealed. The inspection company gets pipe and nothing else.

What comes out is not a marketing number. It is a description of behaviour: which defect types the technology resolves cleanly, which ones sit near its threshold, and how the answer shifts as pipe geometry changes. That is more useful to an asset manager than a headline detection rate, because real pipelines contain a mix of defect types and wall configurations rather than one convenient case.

---

How the SGH study was set up

The paper, Independent Comparison of Electromagnetic Inspection Tools for AWWA C303 Bar-Wrapped Pipe by Blind Verification Testing, was authored by Murat Engindeniz and Alvin Addisho of SGH and discussed with APS Palo Verde Generating Station. You can read the study summary in PICA’s technical paper library or the full paper through the ASCE Library.

The study compared the two electromagnetic methods used in municipal concrete pressure pipe work: Remote Field Technology (RFT) and Near Field Technology (NFT). The two differ in sensor geometry. In NFT the exciter and detector sit close together within the same pipe diameter. In RFT they are separated by two to three pipe diameters, which is what allows the signal to pass through the wall, travel along the outside, and re-enter downstream.

The test pipes

Two above-ground bar-wrapped test pipes were used, 30 inch and 36 inch diameter. Defects were introduced into both the steel cylinder and the reinforcing bars, covering a range of sizes rather than a single severity. PICA ran the pipes with its RAFT and Chimera RFT tools.

The mix mattered. A test built only from large through-holes proves nothing, because every serious tool finds those. Marginal defects are what expose the threshold.

Why bar-wrapped pipe is the demanding case

In prestressed concrete cylinder pipe, a thin steel cylinder is held in compression by high-tension prestressing wires, and broken wires are the leading structural indicator. AWWA C303 bar-wrapped pipe is built differently. The cylinder is thicker, the reinforcement is passive bars rather than tensioned wire, and the cylinder itself carries much more of the structural load.

That has two consequences for inspection. Cylinder wall loss becomes the primary risk, which favours RFT because RFT measures wall thickness continuously. And the thicker cylinder sits between the tool and the bars, which makes bar breaks harder to see. The pipe type that most needs cylinder measurement is also the pipe type that makes bar detection difficult.

---

What the results showed

Where RFT performed

PICA’s RFT tools resolved the significant cylinder damage. Through-holes and areas of section loss were identified, along with metal loss and graphitic corrosion in the steel. For a technology whose main job on bar-wrapped pipe is quantifying cylinder condition, that is the result that counts.

The circumferential accuracy finding is worth more attention than it usually gets. Knowing that a pipeline contains corrosion is of limited use. Knowing that the corrosion sits at the 4 o’clock position on a specific pipe segment is what lets a utility excavate one location and find the defect on the first attempt. The study found PICA’s calibration methods aligned predicted defect positions with actual positions more closely than the compared technology.

PICA’s RFT tools report a minimum defect volume of 1 inch by 1 inch at 20 percent wall loss, and measure through internal linings, scale, cement, epoxy and plastic coatings up to roughly 25 mm thick. No cleaning to bare metal is required.

Where RFT reached its limits

Smaller defects, specifically broken reinforcing bars sitting behind thicker steel cylinders, could be missed. On thinner cylinders the same tool detected bar breaks successfully.

PICA publishes this because it is the useful part. Bar break detection on bar-wrapped pipe depends on cylinder thickness, and that dependency belongs in the scoping conversation rather than in the report.

The physics is straightforward. The signal has to cross the cylinder before it registers anything about the bars outside it. Thicker steel absorbs more of it, so a small bar break becomes harder to separate from ordinary variation in the cylinder. Note that steel gauge numbers run inverse to thickness: a higher gauge number means thinner steel, and 10 gauge equals 0.1345 inches.

What the study said about calibration

SGH found that post-processing and calibration drove a meaningful share of the difference between results. This is where a blind test with reference specimens is genuinely representative of field work, because PICA’s tools can be calibrated against reference specimens with known defect dimensions when sample pipes are available.

Where sample pipe is not available, interpretation rests on project history instead. PICA has more than twenty years of records across pipe materials with metallic components, which is what analysts use to convert signal behaviour into quantified wall loss.

---

From test pipe to buried pipeline

Test pipe results only matter if they hold up in the ground. The companion work does exactly that.

Following a high-consequence pipeline failure, the City of Mesa, Arizona prioritized inspection of its AWWA C303 bar-wrapped mains, covering roughly 1.7 miles of 30 inch and 1 mile of 36 inch pipe. The program paired blind inspection of the above-ground test pipes with field verification in the buried pipelines: locations flagged in the data were excavated and examined directly. That work is documented in High-Resolution Inspection of AWWA C303 Bar-Wrapped Pipe with Detailed Field Verification.

The pattern repeats elsewhere. In a separate 36 inch bar-wrapped inspection, three corrosion indications were identified on the steel cylinder, two of which appeared in the data as potential through-holes at zero percent remaining wall, with approximately six broken bar wraps overlapping those locations. The segment was excavated and removed, and the reported corrosion and broken bars correlated directly with the RFT results. The same validation logic underpins PICA’s work with Tarrant Regional Water District.

---

Why one detection number is not enough

The temptation after a study like this is to extract a single percentage and treat it as the answer. Detection capability on bar-wrapped pipe varies by defect type and by cylinder thickness, and a number generated on one wall configuration does not transfer to another. Any vendor quoting a single accuracy figure across all bar-wrapped pipe is either simplifying or overselling.

The practical response is to match the method to the failure mechanism, and to combine methods where one tool cannot cover everything:

• RFT measures cylinder wall thickness continuously and detects broken bars, cylinder corrosion and loss of pre-load. It is the preferred method for bar-wrapped pipe because cylinder condition dominates the risk. The through-transmission signal sees wall loss on both the internal and external surfaces, though without differentiating between them.
• NFT detects and quantifies 5 or more adjacent broken wires or bars in concrete pressure pipe from 36 to 136 inches out of service. It does not measure cylinder wall thickness, which is why it is used where RFT cannot be deployed rather than as a substitute for it.
• Bracelet Probe and ultrasonic thickness tools quantify wall loss at excavated locations and validate what the in-line data reported.
• CCTV with laser and lidar profiling documents liner condition, joint condition and internal deformation that electromagnetic tools do not see.
• The NAVIGATOR acoustic sphere screens live pipelines for leaks, gas or air pockets and flow restrictions, prioritizing which segments justify a full electromagnetic survey.

PICA maintains both RFT and NFT service offerings for this reason. They are separate services suited to different conditions, not a bundle.

---

What this means for procurement

If you manage bar-wrapped transmission mains, three questions are worth putting to any inspection vendor before award.

First, ask what independent validation exists for the claimed accuracy, and who performed it. Self-reported results and third-party blind results are not the same evidence.

Second, ask what the technology does not detect on your specific pipe. Cylinder thickness, liner type and diameter all change the answer. A vendor who cannot describe the limits either has not tested them or would rather not say.

Third, ask how reported locations will be verified. Excavating a flagged location and comparing what is found against what was reported is the only field check that closes the loop, and it belongs in the program plan rather than in a dispute afterward.

For the underlying technology rather than the validation evidence, start with Understanding RFT for Bar-Wrapped Pipelines, which covers how the method works and what RFT data looks like in practice.

---

Frequently asked questions

What is blind verification testing in pipeline inspection?

Blind verification testing is a controlled trial in which defects of known size and position are built into test pipe and withheld from the inspection vendor. The vendor runs its tool and submits findings, and a third party scores those findings against the defect record. Because the vendor cannot tune its analysis toward a known answer, the results show what the technology actually resolves rather than what it resolves under favourable conditions. For buyers, it is one of the few ways to compare inspection vendors on evidence instead of marketing claims.

Who conducted the AWWA C303 electromagnetic inspection comparison?

The study was carried out by Simpson Gumpertz & Heger Inc., an independent engineering firm, and authored by Murat Engindeniz and Alvin Addisho. It compared Remote Field Technology and Near Field Technology across two inspection vendors, one of which was PICA Corp. Testing used 30 inch and 36 inch bar-wrapped pipe with defects introduced into the steel cylinders and reinforcing bars. Results were presented at the UESI Pipelines 2024 Conference in Calgary and published through the ASCE Library.

What did the blind test show about RFT detecting broken bars?

RFT reliably identified the larger defects in the steel cylinder, including through-holes and areas of section loss. Broken reinforcing bars sitting behind a thicker steel cylinder were the harder case, and smaller damage of that type could be missed. On thinner cylinders, RFT detected bar breaks successfully. The practical conclusion is that detection capability on bar-wrapped pipe is a function of cylinder thickness, not a single fixed number that applies to every pipe.

Why does steel cylinder thickness affect electromagnetic inspection results?

An electromagnetic signal has to pass through the steel cylinder before it can register anything about the reinforcing bars wrapped outside it. A thicker cylinder absorbs more of that signal, so the contribution from a small bar break becomes harder to separate from normal variation in the cylinder itself. Thinner cylinders leave more signal available and produce clearer bar break indications. Note that steel gauge numbers run inverse to thickness: a higher gauge number means thinner steel, and 10 gauge equals 0.1345 inches.

What is the smallest defect RFT can report?

The minimum reported defect volume for PICA’s RFT tools is 1 inch by 1 inch at 20 percent wall loss. RFT measures through internal linings, scale, cement, epoxy and plastic coatings up to about 25-30 mm, roughly 1 inch thick, so the pipe does not need to be cleaned to bare metal. One limitation matters for interpretation: the through-transmission signal sees wall loss on the internal surface and the external surface simultaneously, without differentiating between the two.

How is AWWA C303 bar-wrapped pipe inspected?

Bar-wrapped pipe is inspected with electromagnetic tools run inside the pipeline. RFT is the preferred method because the steel cylinder carries more structural load in bar-wrapped pipe than in prestressed concrete cylinder pipe, and RFT measures cylinder wall thickness continuously. PICA runs in-service RFT tools including the SeeSnake and Chimera from 2 to 36 inches, and out-of-service tools including RAFT from 36 to 48 inches and EMIT from 48 to 96 inches. NFT is used where RFT cannot be deployed, and detects 5 or more adjacent broken bars but does not measure cylinder wall thickness.

Can bar-wrapped pipe failures be prevented?

Yes, in most cases. Corrosion of the steel cylinder in bar-wrapped pipe develops over years and produces measurable wall loss long before pressure capacity drops to failure. The difficulty is that nothing shows on the surface, so a pipeline can look sound while the cylinder is thinning. Continuous wall thickness measurement identifies which pipe segments have lost section and by how much, which lets a utility repair or replace specific segments rather than waiting for a break or replacing the whole main.

How much does bar-wrapped pipe inspection cost?

Inspection programs for concrete pressure pipe range from tens of thousands to hundreds of thousands of dollars per mile. Large-diameter out-of-service electromagnetic programs typically run from 100,000 to 200,000 dollars or more per mile, driven by diameter, linear footage, access complexity, the number of inspection tiers involved and mobilization distance. Set against that, inspection typically costs 10 to 50 times less than an unplanned failure on the same segment, before service outage and environmental exposure are counted.

---