What NDT means in oil and gas

In oil and gas, nondestructive testing is mostly about containment. Pipes, vessels, tanks, wells and pipelines are built to hold fluids under pressure, and in service they are attacked from inside by what they carry and from outside by soil, seawater, weather and insulation that traps water. Inspection answers three questions again and again: is it made right, how fast is it wearing out, and is it still fit to run until the next look?

Most of the work falls into two kinds. Construction inspection checks new welds, materials and coatings before equipment goes into service. In-service inspection measures what time and the process have done since, so that corrosion, cracking and other damage are found and managed before they cause a leak.

One industry, three segments

The industry is usually described in three parts, and each has its own equipment, its own damage and its own regulator. We cover each in its own article.

  • Upstream (coming soon) finds and produces oil and gas: drilling rigs and drill pipe, well casing and tubing, wellheads and pressure-control equipment, and onshore and offshore production facilities. Fatigue, wear and corrosion of tubulars and structures dominate.
  • Midstream (coming soon) moves and stores it: transmission and gathering pipelines, compressor and pump stations, terminals, storage tanks and LNG facilities. Pipeline integrity management, in-line inspection and girth-weld inspection are central.
  • Downstream turns it into products: refineries, and the terminals and distribution systems beyond them. Process damage mechanisms, risk-based inspection and turnarounds shape the work.

The methods you will see everywhere

A few methods do most of the work across all three segments. Ultrasonic thickness measurement tracks wall loss at fixed monitoring points. Phased array ultrasonics and radiography examine welds. Magnetic particle and penetrant testing find surface cracks. Visual inspection comes first and last. Magnetic flux leakage and ultrasonic tools inspect pipelines from the inside, and electromagnetic and ultrasonic techniques inspect heat exchanger tubes, which our guide to tubing analysis covers in detail.

What changes from one segment to the next is less the method than the question being asked, the acceptance criteria being applied, and who has to be satisfied with the answer.

Who sets the rules

  • Offshore: BSEE regulates safety on the US Outer Continental Shelf, including platform inspection reporting under 30 CFR Part 250.
  • Pipelines: PHMSA regulates gas pipelines under 49 CFR Part 192 and hazardous liquid pipelines under Part 195, including when welds must be examined and how pipelines in high consequence areas must be assessed.
  • Refineries and processing plants: OSHA's Process Safety Management standard (29 CFR 1910.119) and EPA's Risk Management Program (40 CFR Part 68) both require mechanical integrity programs with documented inspection and testing.
  • Industry codes: API publishes most of the inspection codes and recommended practices, from drill pipe to storage tanks and refinery piping, and ASME publishes the pressure vessel and piping codes many of them build on.

Two kinds of people usually share the work. NDT technicians, certified by their employers to programs such as ASNT's SNT-TC-1A, perform and interpret the examinations. API-certified inspectors, among others, use those results to judge equipment against the inspection codes. Our guide to API inspector certifications explains how those roles fit together.

Frequently asked questions

What is NDT in oil and gas?

It is the use of inspection methods such as ultrasonic testing, radiography, magnetic particle and eddy current testing to check wells, pipelines, tanks, vessels and piping for flaws and wall loss without damaging them, both when they are built and throughout their service life.

Which NDT method is most used in oil and gas?

Ultrasonic testing is the workhorse, and ultrasonic thickness measurement at fixed monitoring locations is one of the most frequent tasks, because corrosion rate and remaining wall thickness drive so many inspection decisions. Weld examination by radiography or phased array ultrasonics is the other big area.

How NDT LLC can help

NDT LLC helps operators, owners and inspection companies across oil and gas with NDT procedures and written practices, personnel qualification, independent review of inspection data, and audit readiness. Contact us to talk about your program.

This article is general information for a business audience, not engineering, legal or regulatory advice. Always work to the current edition of the codes, standards, regulations and manufacturer data that apply to your equipment and contracts.

NDT LLC is an independent consulting firm. It is not affiliated with, endorsed by or sponsored by the American Petroleum Institute (API), ASME, PHMSA, BSEE, OSHA, EPA, ASNT, or any other organization named in this article; names are used only to identify the organizations and documents referred to.