UT Level I: Calibrate, Test, Record — and Why You Do Not Evaluate
A UT Level I in Pasadena performs calibrations and specific ultrasonic tests under written instruction, records readings and indications, and hands the evaluation to a Level II. SNT-TC-1A recommends 40 hours of classroom training and about 210 hours of documented ultrasonic experience before examination, but the employer's written practice is the controlling document and may set more.
Pasadena sits on the south bank of the Houston Ship Channel, wrapped in tank farms, chemical plants, marine and barge terminals, and the pipe and vessel fabrication shops that feed them. Ultrasonic testing is the method that keeps that base running, and most of the hours are Level I hours: thickness routes on piping and vessels, weld scanning under a Level II's instruction, calibration checks at the start and end of every shift. The level is often misdescribed as junior. It is better described as bounded. A Level I is expected to calibrate correctly, follow a written instruction exactly, record what the instrument shows, and stop short of judging it. That boundary is where the audit findings land, because a Level I who quietly evaluates has invalidated the report and the employer's written practice at the same time.
Source: ASNT SNT-TC-1A, Sections 6, 7 and 8 and Tables 6.3.1A and 6.3.2; ANSI/ASNT CP-189; ISO 9712:2021, Annexes A and B; ASME BPVC Section V, Article 4 (ultrasonic examination of welds) and Article 5 (ultrasonic examination methods for materials); ASME BPVC Section VIII Division 1, Mandatory Appendix 12; ASME B31.3 para. 344.6; ASTM E797, thickness measurement by manual contact pulse-echo; ASTM E317, system performance evaluation; ASTM E164.
| Task | Level I | Level II | Controlling document |
|---|---|---|---|
| Set velocity and zero offset on a calibration block | Performs and records | Performs and verifies | Written examination procedure |
| Construct a DAC curve from side-drilled holes | Performs under written instruction | Performs and validates the setup | ASME Section V Article 4, written procedure |
| Record wall thickness at condition monitoring locations | Performs and records | Reviews and trends | Inspection data management plan |
| Decide whether an indication is relevant or geometric | Not permitted | Performs | Employer written practice |
| Evaluate an indication against code acceptance criteria | Not permitted | Performs | ASME Section VIII Div 1 App 12, B31.3 344.6 |
| Sign the examination report | Only if the written practice expressly allows, under Level II review | Signs | Employer written practice |
| Set up equipment for another technician's scan | Performs | Performs and approves | Written examination procedure |
What a UT Level I Is Allowed to Do
SNT-TC-1A describes a Level I as qualified to perform specific calibrations, specific tests and specific evaluations for acceptance or rejection determined by written instructions, and to record results — with the essential qualifier that a Level I receives the necessary instruction or supervision from a certified Level II or Level III. That sentence is doing a lot of work. It permits a Level I to apply a decision rule someone else has written, but it does not permit the Level I to form the judgement behind it.
In practice on the Houston Ship Channel that resolves to a clear split. A Level I calibrates the instrument, verifies it against a block, prepares the surface, executes the scan pattern the procedure sets out, and records amplitude, metal path, surface distance, depth and extent. A Level II characterises what has been recorded and applies the code acceptance table. When a Level I finds something unexpected, the correct action is to record it and escalate, not to resolve it.
The reason this boundary is drawn so firmly is legal as much as technical. An examination report carries the certification level of the person who signed it, and a client auditing a rejected or missed indication will trace it back to that signature. If the file shows evaluation performed by a Level I, the report is defective regardless of whether the call was correct. Employers who blur this to save a Level II's time create a liability that surfaces months later.
Velocity, Zero and the Two-Point Calibration
Everything ultrasonic starts with velocity. The instrument measures time; thickness and metal path are calculated by multiplying that time by an assumed material velocity and halving it for the round trip. Longitudinal velocity in carbon steel is around 5,900 metres per second, roughly 0.232 inches per microsecond; shear velocity is a little over half that. Aluminium is faster, water far slower. Assume the wrong velocity and every number the instrument reports is wrong by the same proportion.
Zero offset is the second half of the pair. It accounts for the delay through the probe wear face, delay line or wedge, and through the couplant layer, none of which is material under test. A two-point calibration on a step wedge — a thin step and a thick step spanning the expected range — solves for velocity and zero together and is the routine every thickness technician should be able to perform without reference to a manual. A single-point calibration solves for one unknown and hides the other.
Calibration is not a start-of-day formality. Written procedures normally require verification at the start of the shift, at defined intervals, after any change of probe, cable or setting, and at the end of the shift or the end of the examination. If the end-of-shift check fails, the readings taken since the last good check are suspect and the procedure will say what to do about them. A Level I who logs calibration checks properly protects an entire shift's data.
DAC and DGS: What a Level I Sets Up and What a Level II Reads
For amplitude-based flaw evaluation, a distance amplitude correction curve is built by recording the response from an identical reflector — typically a side-drilled hole in a reference block — at a series of increasing metal paths, then joining the peaks. The curve compensates for attenuation and beam spread with distance, so an indication at 60 millimetres metal path can be compared meaningfully against one at 20. A Level I is commonly the person who builds it, following the procedure's block, hole size and point spacing.
The distance gain size approach works differently. Rather than an empirical curve from a specific block, DGS uses a set of theoretical curves relating distance, gain and equivalent flat-bottomed-hole size for a characterised probe, letting the operator express an indication as an equivalent reflector size. It is faster to set up and probe-specific, which means the probe characteristics must match the curves being used. Substituting a nominally similar probe invalidates the sizing.
Both approaches share a trap that catches Level I candidates in practical examinations: the setup is only valid within the conditions it was established under. Change the gain, the probe, the wedge, the couplant or the surface condition, and the reference is no longer a reference. Building the curve is a Level I task; deciding that a given curve is appropriate for a given component, and reading an indication against it to an accept or reject decision, is not.
Thickness Measurement and the Errors That Bite Level I
Straight-beam thickness measurement looks like the simplest thing in ultrasonics and produces more bad data than anything else. Doubling is the headline error: the instrument's gate catches the second back-wall echo rather than the first, or a heavily corroded back wall scatters the true return, and the reading lands at an implausible multiple of nominal. Any reading that is close to half or double what the drawing says is re-taken, on a different probe, with the A-scan visible rather than the digital readout alone.
Coating is the second. A paint or coating layer has a different velocity from steel, so a single-element probe calibrated for steel will add an apparent thickness that varies with coating thickness. Echo-to-echo measurement between successive back-wall echoes removes the coating from the measurement and is the correct technique on painted surfaces — the procedure should say so. Dual-element probes with a roof angle are used for corroded back walls because they tolerate rough, non-parallel surfaces that a single element cannot.
Then geometry and temperature. Small-diameter piping curves away from the probe and produces a weak, misleading return unless the probe is oriented correctly relative to the axis. Hot lines change material velocity — it falls as temperature rises — so hot readings need the correction the procedure specifies and high-temperature couplant and delay lines. And every instrument has a minimum measurable thickness set by its dead zone and probe; a reading below that limit is not a thin wall, it is an artefact.
Couplant, Surface Condition and Transfer Correction
Ultrasound does not cross an air gap. Couplant exists to bridge the acoustic impedance mismatch between the probe face and the component, and its selection is a procedure decision rather than a convenience. Glycerine, cellulose gels, water and oils all have different viscosities, temperature ranges and cleaning requirements. On austenitic stainless steel and nickel alloys, the couplant must be certified for halogen and sulphur residue because those contaminants can drive stress corrosion cracking in service — and the certificate for the batch in use is a routine audit request.
Surface condition changes results in ways that are easy to underestimate. Roughness scatters energy and reduces coupling, so amplitude falls even where the material is sound. Curvature reduces contact area. Mill scale, loose rust, weld spatter and thick coating all reduce transmission. Preparation is not cosmetic — on a corrosion mapping scope, the difference between a wire-brushed surface and a properly prepared one shows up directly in the number of locations that cannot be read.
Transfer correction is the formal answer to this. It quantifies the difference in signal loss between the calibration block and the actual test piece and adjusts the gain accordingly, so an amplitude evaluation established on a smooth reference block still means something on a rough, coarse-grained or coated component. A Level I applies it when the procedure requires it, using the specified method. Judging whether it is required, and how much correction is defensible, belongs to Level II and above.
Training, Experience and the Examinations for UT Level I
The recommended route under SNT-TC-1A is around 40 hours of organised classroom training in ultrasonics plus roughly 210 hours of documented ultrasonic experience for a high school graduate, with reductions available for candidates who have completed relevant engineering or science study beyond high school. ISO 9712 asks for a comparable 40 hours of training and about three months of industrial experience in the method. The employer's written practice is the controlling document and may require more; it should never require less without documented justification.
Examination is in three parts. The general examination covers ultrasonic principles — wave modes, velocity, refraction and Snell's law, attenuation, beam spread, near and far field, probe types, pulse-echo and through-transmission, calibration blocks. Under SNT-TC-1A's recommended minimums, ultrasonics carries a larger general examination than the surface methods, typically around 40 questions, with a shorter specific examination of about 20 questions covering the employer's own procedures, instruments and codes.
The grading rule is a composite of at least 80 percent with no individual examination below 70. Candidates fail more often on the specific examination than the general, because they study ultrasonic theory from a textbook and never read their own employer's written procedures. If you are preparing for a Level I examination in Pasadena, ask for the procedure numbers you will be examined on and read them. That single step changes pass rates more than any additional theory revision.
What the Practical Examination Actually Involves
The practical examination is where preparation shows. The candidate is given equipment, a calibration block and one or more specimens, and is graded against a minimum of ten checkpoints covering equipment operation, calibration, technique and the recording of results. It is a demonstration, watched in real time. Examiners are watching sequence and habit as much as outcome: whether you verify the instrument before you start, whether you record settings, whether you clean and re-couple rather than dragging a dry probe.
For a UT Level I the checkpoints typically include performing a two-point calibration and demonstrating it holds, setting up for the specified technique, scanning the specimen with adequate overlap, locating indications the examiner has already characterised, and recording metal path, surface distance, depth and amplitude in the format the procedure requires. Repeatability is often tested by asking for a second pass and comparing. A candidate whose second set of numbers differs materially from the first has not demonstrated control of the technique.
The failure mode is nearly always speed. Candidates who have done the work in the field for months move fast, skip the verification step, and lose points on process rather than on detection. The examination is not measuring how quickly you can find the flaw; it is measuring whether you follow the procedure under observation. Slow down, narrate what you are doing, and record as you go rather than reconstructing at the end.
Pasadena, Texas: Where UT Level I Work Actually Is
Pasadena's industrial character is defined by its position on the south side of the Houston Ship Channel. The base is petrochemical and refining, storage and distribution: tank farms, chemical process units, marine and barge loading terminals, pipeline gathering and distribution, and a dense supporting layer of pipe fabrication shops, vessel and exchanger shops, and structural fabricators serving both onshore plants and offshore construction. The city also feeds the corridor a steady supply of process technicians through its community college pipeline, and NDT recruits heavily from the same pool.
That base generates ultrasonic Level I hours in three main forms. Thickness routes on piping circuits and vessels in operating plants, run on a schedule set by the in-service inspection programme. Shop inspection on new fabrication, where welds are examined before shipment and the volumes are high and repetitive — good conditions for accumulating documented experience quickly. And tank and terminal work, where shell thickness, seam integrity and floor condition all draw on ultrasonics alongside other methods.
For someone starting out, the shop route is usually the fastest way to real hours, because the work is continuous and supervised and the specimens vary enough to build genuine technique. Plant thickness routes teach discipline and data quality. Neither, by itself, produces a rounded Level II — that requires exposure to both, plus weld scanning under a Level II, which is why written practices set method experience in hundreds of hours rather than in weeks of employment.
Can a UT Level I accept or reject a weld?
No. Acceptance and rejection require evaluation against code criteria, and evaluation is a Level II function under every mainstream written practice. A Level I calibrates, scans to a written instruction, and records what the instrument shows — amplitude, metal path, surface distance, depth, extent. The Level II decides whether that indication is geometric or relevant and whether it is rejectable. A Level I who writes an accept or reject conclusion has stepped outside the certification the employer issued.
How many training hours does UT Level I require?
SNT-TC-1A's recommended minimum for a high school graduate is about 40 hours of organised classroom training, with roughly 210 hours of documented ultrasonic experience before examination. ISO 9712 expresses the same requirement as 40 hours of training and around three months of industrial experience in the method. Both are minimums that an employer's written practice may exceed. Neither substitutes education for method-specific experience: the hours must be ultrasonic hours.
Why does a thickness gauge read exactly half the wall?
That is doubling. On thin sections, or when the first back-wall echo is weak, the instrument's gate can lock onto the second back-wall echo instead of the first, reporting twice the transit time interpreted at half the expected place — or, in the classic field version, a corroded back wall gives a reading that is a neat fraction of nominal. Any reading that lands suspiciously close to half or double nominal is re-taken with a different probe and verified against an A-scan.
What is transfer correction and when does a Level I apply it?
Transfer correction accounts for the difference in signal loss between the calibration block and the actual test piece — different surface roughness, coating, curvature, grain structure and attenuation. Without it, an amplitude-based evaluation calibrated on a smooth block will under-call indications in a rough, corroded, or coarse-grained component. A Level I applies it when the written procedure requires it, using the technique the procedure specifies. Deciding whether it is needed at all is a Level II or Level III call.
Does a UT Level I need a certified couplant?
On austenitic stainless steel and nickel-base alloys, yes — the couplant must be certified for halogen and sulphur residue, because those contaminants can promote stress corrosion cracking in service. The certificate travels with the batch and auditors ask for it. On carbon steel the requirement is looser, but the practical concerns remain: consistent coupling, appropriate viscosity for the surface and orientation, temperature rating for hot lines, and removal afterwards where the client requires it.
Is API 510, 570 or 653 inspector training part of this offer?
No. Atlantis NDT does not deliver API 510, API 570 or API 653 inspector certification training, and is not the API inspector of record or a PSM auditor. Those are inspector credentials, distinct from NDT method certification. What we deliver is ultrasonic testing training and certification preparation at Levels I, II and III to ASNT SNT-TC-1A and ISO 9712, alongside the other methods, plus ASNT Level III consulting support for written practices.