What can go wrong upstream

Upstream equipment faces a different mix of damage from the plants further down the chain:

  • Fatigue in rotating drill pipe and in the threaded connections of the drill string, which bend with every rotation in a curved hole, and in offshore structural joints loaded by waves.
  • Wear and mechanical damage: worn tool joints, eroded pipe, slip and tong marks, and handling damage to tubulars.
  • Corrosion from produced water, carbon dioxide and oxygen, and in sour wells, hydrogen sulfide cracking of susceptible steels.
  • Seawater corrosion of offshore structures, worst in the splash zone where the steel is alternately wet and dry.

Failures here can mean a lost string and a costly fishing job, a well integrity problem, or on an offshore installation, damage that threatens the whole structure.

Drill string inspection

Used drill pipe, heavy-weight drill pipe, drill collars and the rest of the drill stem are inspected at intervals between wells to find fatigue cracks, wall loss and worn connections before they fail downhole. API RP 7G-2 is the recommended practice for inspecting and classifying used drill stem elements. It defines levels of inspection and the methods to use, and it classifies drill pipe (for example as Premium Class or Class 2) by remaining wall and condition, which in turn governs how it may be used.

The methods are a mix:

  • Visual inspection and dimensional checks of the tube, tool joints and threads.
  • Electromagnetic inspection (EMI) of the pipe body, in which a buggy runs along the pipe using flux leakage and related sensors to find cracks, pits and wall loss.
  • Ultrasonic testing (UT) for wall thickness and to prove up EMI indications, and in the slip and upset areas where cracks tend to start.
  • Magnetic particle testing (MT), often wet fluorescent, on threaded connections and tool joints, where fatigue cracks start at the thread roots.

Casing, tubing and other OCTG

Oil country tubular goods (OCTG), the casing, tubing and pipe that line and produce a well, are inspected at the mill and, often, again before they are run. API Specification 5CT sets manufacturing and inspection requirements for new casing and tubing, including the nondestructive testing mills perform. Field inspection of new tubulars before use, to catch damage in transport and storage and any mill defects that slipped through, follows practices such as API RP 5A5. Used tubing pulled from wells is inspected to decide whether it can be rerun.

Wellheads and pressure-control equipment

Wellheads, trees, valves and blowout preventers contain full well pressure. They are built to API specifications such as API 6A for wellhead and tree equipment, which set material, examination and testing requirements during manufacture. In service, they are pressure tested and inspected at intervals, and remanufactured with full examination of critical parts. Surface NDT such as magnetic particle and penetrant testing, ultrasonic examination of forgings and welds, and dimensional checks of wear surfaces all play a part.

Offshore platforms

Fixed and floating offshore structures are inspected above and below water throughout their lives. In US federal waters, BSEE requires operators to submit an in-service inspection report every year, by November 1, listing the platforms inspected in the previous twelve months, the extent of inspection above and below water, the type of inspection used, such as visual, magnetic particle or ultrasonic testing, the overall structural condition including corrosion protection, and any repairs needed (30 CFR 250.919). BSEE's platform rules draw on API recommended practices such as API RP 2A-WSD for fixed platforms and API RP 2SIM for structural integrity management.

Underwater, much of the work is done by divers or remotely operated vehicles: general visual surveys, cathodic protection readings, close visual inspection of critical welded nodes, and where needed, cleaning and crack detection with magnetic particle testing or alternating current field measurement (ACFM), which can find surface cracks through coatings. Flooded member detection, by ultrasonic or radiographic means, checks whether a tubular brace has filled with water, a sign that it has cracked through. Topsides, the process piping and vessels are inspected much like an onshore plant.

Regulations and standards

  • BSEE regulations in 30 CFR Part 250 govern offshore facilities on the US Outer Continental Shelf, including platform design, inspection and assessment, and incorporate API recommended practices by reference.
  • API publishes most of the equipment specifications and recommended practices: tubulars (5CT, 5DP), drill stem inspection (RP 7G-2), wellhead equipment (6A), well control equipment (Standard 53) and offshore structures (the RP 2 series).
  • Sour service materials are selected to ANSI/NACE MR0175/ISO 15156, now maintained with AMPP, which limits hardness and sets other requirements so steels resist sulfide stress cracking.
  • Onshore, OSHA's Process Safety Management standard does not apply to oil or gas well drilling and servicing operations, or to normally unoccupied remote facilities, so many producing sites are managed under operators' own integrity programs and other rules.

What this means for operators and contractors

Upstream inspection is often done by specialist contractors on tight schedules, between wells or during a short weather window. Ask whether the inspection company's procedures match the recommended practice and your own specification, whether its technicians are certified in the specific technique (EMI, UT, wet fluorescent MT), whether its equipment is calibrated against traceable reference standards, and whether inspected pipe is marked and reported so its class is clear to the rig. For offshore work, make sure the annual inspection data is complete enough to support the report and the next year's plan.

Frequently asked questions

How is drill pipe inspected?

Used drill pipe is typically inspected visually and dimensionally, with electromagnetic inspection of the tube body for cracks and wall loss, ultrasonic testing to measure wall and prove up indications, and magnetic particle testing of the threaded connections. API RP 7G-2 sets out the recommended practice and how pipe is classified by its condition.

What is OCTG inspection?

It is the inspection of oil country tubular goods, the casing, tubing and pipe used in wells. New pipe is inspected at the mill and often again before it is run, and used pipe is inspected to decide whether it can go back in a well.

How are offshore platforms inspected?

By visual surveys above and below water, cathodic protection measurements, close inspection of critical welded joints with methods such as magnetic particle testing or ACFM, and checks for flooded members. In US federal waters, operators report their inspections to BSEE every year.

How NDT LLC can help

NDT LLC helps drilling contractors, operators and inspection companies with NDT procedures and written practices, technician qualification, audits of inspection vendors and independent review of inspection data. Contact us to talk about your program. For the rest of the value chain, see our overview of NDT in oil and gas and the articles on midstream and downstream.

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), BSEE, AMPP, ISO, OSHA, or any other organization named in this article; names are used only to identify the organizations and documents referred to.