Ultrasonic testing for welds, wall thickness and corrosion

• Conventional pulse echo UT: a single element probe, straight beam for thickness and laminations, angle beam for welds. Flexible, portable and inexpensive, but results depend heavily on the operator.
• Phased array ultrasonic testing (PAUT): an array probe steers and focuses the beam electronically, producing sector and linear scans. Encoded scans create a permanent, reviewable record of the weld.
• Time of flight diffraction (TOFD): two probes pick up signals diffracted from flaw tips, which gives accurate through wall height sizing. Often paired with PAUT for full weld coverage.
• Ultrasonic thickness gauging: spot readings of remaining wall on piping, vessels and tanks, the basis of many corrosion monitoring programs.
• Immersion UT and C-scan: the part sits in a water tank while a probe rasters over it, producing a plan view map. Common for aerospace forgings, composites and bonded structures.
• Corrosion mapping: encoded scanners record thickness over an area as a color map, so you see the shape and depth of wall loss rather than a few points.

UT is everywhere metal carries pressure or load. Refineries and chemical plants run thickness monitoring under API 570 for piping and API 510 for vessels, and tank floors and shells are checked under API 653. Fabrication shops and construction projects use angle beam and PAUT for welds under ASME and AWS D1.1. Power plants inspect boiler tubes, headers and turbine components. Aerospace uses immersion UT on forgings and composites. Pipelines rely on PAUT and AUT for girth welds and on corrosion mapping at digs. See oil and gas inspection services and power plant inspection services for sector specific notes.

Many construction codes allow UT in place of radiography when it is performed with qualified procedures. ASME Section V Article 4 covers UT of welds, and ASME code cases and Section VIII rules govern when UT can replace RT and with what acceptance criteria. AWS D1.1 includes its own UT clauses for structural steel. PAUT and TOFD avoid radiation exclusion zones, so other trades keep working, and encoded data can be audited later. The trade off is the need for a written, often demonstrated procedure and well qualified operators, because flaw characterization relies on interpretation.

1. You describe the component: material, thickness, geometry, access, temperature and the question (weld acceptance, minimum wall, corrosion extent).
2. The provider selects technique and writes or confirms the procedure, including calibration blocks, probes and scan plan.
3. Surface preparation is agreed: removing loose scale or coating where needed.
4. Technicians scan on site or in the lab. Encoded PAUT, TOFD and corrosion mapping data are saved for review.
5. A Level II or Level III analyst evaluates indications against acceptance criteria or computes remaining wall.
6. You receive a report with locations, sizes, thickness grids or C-scan maps and accept or reject calls.

Thickness surveys and conventional weld checks often finish within the visit. Advanced data analysis and reporting usually adds 2 to 5 business days.

Field UT is usually priced by technician day rate, with a higher rate for PAUT, TOFD and corrosion mapping because of equipment and data analysis. Access is the big variable: scaffolding, insulation removal, rope access and confined space entry can cost more than the inspection itself. Lab immersion work is priced per part or per hour after a fixture and scan plan exist.

Mobilization, travel, per diem and access costs are usually extra.

Ask for UT Level II personnel for the specific technique, since a conventional UT certification does not cover PAUT or TOFD. For refining and petrochemical work, owners often require API QUTE for thickness and API QUPA for phased array flaw sizing, alongside API 510, 570 or 653 inspector involvement. Aerospace work calls for NAS 410 personnel and NADCAP accreditation covering ultrasonic. For lab testing, check that UT sits inside the ISO/IEC 17025 scope. Ask whether procedures have been demonstrated or qualified for your thickness range and material.