Pressure vessel inspection checklist: external, internal and records

It is a working aid and a study aid. The rules you inspect to come from API 510 and your owner/user's inspection program, and the practices behind each item are described in API RP 572, so keep your own copies at the editions on the effectivity sheet. Where a block below maps to a part of those documents, the last column of the reference table gives the section number only.

Before you go: records and safety

Pull these first. Most surprises show up in the file before they show up on the vessel.

☐	Item	Why it matters
☐	Last inspection report and its recommendations	Tells you what was open, what was deferred and what to look at again
☐	Thickness readings by location, with dates and the required thickness	You cannot judge a reading without the ones before it
☐	Corrosion rates and remaining life from the last cycle	Shows which locations are driving the interval
☐	Nameplate data, design conditions and the data report	MAWP, temperature, material and joint category set what "acceptable" means
☐	Process conditions and any change since the last inspection	A new fluid, higher temperature or upset changes which damage to expect
☐	Repair, alteration and rerate history	Patches, added nozzles and changed ratings are places to look closely
☐	Relief device records and the last test result	The device protects the vessel at the MAWP you are checking against
☐	Drawings, insulation and lining details	Tells you where metal is hidden and what you will have to open up
☐	Entry permit, isolation and atmosphere testing in place	Internal work is confined-space work; nobody enters until these are done

If a document is missing, write that down. A gap in the history is a finding, not an inconvenience.

External: walk it from the ground up

Start at grade and work upward and around, with a flashlight even in daylight.

☐	Look at	Typical trouble
☐	Foundation, anchor bolts, skirt or saddles	Cracked grout, loose or corroded bolts, settlement, wet corrosion where a saddle sits on the shell
☐	Insulation and jacketing	Torn or missing jacketing, stains, sagging, sealant gone at penetrations and seams, wet insulation
☐	Paint and coatings on bare metal	Blistering, rust bleed, coating failure at low ledges and under supports
☐	Shell and heads	Dents, bulges, gouges, arc strikes, weld-toe cracking, any change in shape since last time
☐	Nozzles, manways and flanges	Leaks, weeping gaskets, bolting condition, corrosion at the nozzle neck and reinforcing pad edge
☐	Small-bore connections and attached piping	Vibration cracks at fittings, unsupported weight on nozzles, missing plugs
☐	Ladders, platforms and attachments	Clips and pads welded to the shell where moisture collects and cracks start
☐	Grounding, nameplate and stamping	Nameplate legible, attached and matching the records
☐	Relief devices and their discharge path	Correct device and tag, nothing blocking the inlet or outlet, drain open, no signs of past discharge or leaking at the seat
☐	Leaks and stains of any kind	Trace each one to its source before you move on

Insulated vessels deserve extra time. Water gets past jacketing at nozzles, support rings, skirts and the low side of the shell, and the steel under it can lose metal while the outside looks fine. Our damage mechanisms guide describes corrosion under insulation and where it tends to be found, and the post on what inspectors look for with corrosion under insulation goes through the warning signs and the follow-up methods.

Internal: only after the vessel is made safe

An internal look covers surfaces you cannot reach in service. Clean surfaces first, because scale and deposits hide pitting and cracks.

☐	Look at	Typical trouble
☐	Overall surface condition	General thinning versus local pits, grooves or a clear flow pattern
☐	Liquid line, vapor space and the bottom	Corrosion often differs by zone: pitting at the liquid line, deposits and under-deposit attack at the bottom
☐	Weld seams and heat-affected zones	Cracks, undercut, local corrosion beside a weld; surface methods follow up on anything suspect
☐	Inlet and outlet nozzle areas and the surface opposite them	Erosion and impingement where flow turns or speeds up
☐	Internals: trays, baffles, distributors, supports, demisters	Loose, missing or corroded parts; fouled or plugged passages
☐	Linings, cladding and refractory	Blisters, cracks, disbonding, holidays and spalling; corrosion behind a failed lining
☐	Bottom drains, sumps and dead legs	Water and solids collect here, so attack is often worst here
☐	Heating or cooling surfaces and tube-side access, where fitted	Fouling, tube end corrosion, leaking or plugged tubes
☐	Anything removed or added since the last entry	Repairs and new attachments need close attention and records

When the conditions the code sets for it are met, an on-stream inspection can stand in for an internal one. The Section 6 rules for that live in your own copy of API 510, so read them there instead of working from memory.

On-stream: what you can still do while it runs

On-stream work is mostly the external checklist plus measurement from the outside.

• Repeat the external walk, with attention to leaks, vibration and anything that changed with operating conditions.
• Take thickness readings at the condition monitoring locations, from the same marked points with the same technique each time.
• Use ultrasonic or radiographic methods at suspect spots, and surface methods for cracks, as your inspection plan calls for.
• Check operating records against the design limits: pressure, temperature and any excursions since last time.
• Never loosen bolting or open a connection on a vessel in service as part of an inspection.

Thickness monitoring

A reading means little alone. A set of readings with dates means a rate, and a rate gives remaining life.

☐	Check	Notes
☐	Readings taken at the marked locations, not near them	Mark the spot so the next person reads the same one
☐	Same instrument, calibration check and technique recorded	Gauge differences look like corrosion or fake a gain
☐	Any reading higher than last time flagged	Wall does not grow back; look for a gauge, surface or location problem
☐	Rates calculated from actual dates	Long-term and short-term rates, both kept
☐	Remaining life and next due date worked out	The worst location sets the date, not the average
☐	Locations still cover the damage you expect	Add locations where a new mechanism is possible

How to choose and space locations is covered in condition monitoring locations explained. For many readings at once, the thickness survey analyzer gives rates and remaining life per location and flags the limiting one. For a single point, use the corrosion rate calculator, the remaining life calculator and the inspection interval calculator. If the numbers lead to a pressure question, the MAWP and thickness calculator checks the wall against a pressure, and the static head calculator covers the elevation step.

Where damage tends to be, by location

This is a reading aid, not a substitute for the mechanism paragraphs. The mechanisms named here are on API's RP 571 list for the current exam window; the damage mechanisms guide gives each one's paragraph number.

Location	What to expect	Mechanisms to think about
Shell under insulation, nozzles, supports	Metal loss under wet insulation, often hidden until it is stripped	Corrosion under insulation (including chloride stress corrosion cracking of 300-series stainless), atmospheric corrosion
Saddles, skirts, ledges, nameplate edges	Wet corrosion where water sits	Atmospheric corrosion
Welds and heat-affected zones in cracking services	Fine cracks at welds that were not stress relieved, in amine, caustic or wet sour service	Amine and caustic stress corrosion cracking, wet H2S damage
Inlet nozzles and the wall opposite them, internals	Local thinning where flow turns or speeds up	Erosion and erosion-corrosion
Liquid line, bottom, dead legs	Pitting, grooving and under-deposit attack	Service-specific corrosion; check the process data
Cold or low-temperature service, startup and shutdown	Cracking from sudden loading at low temperature	Brittle fracture

Practice naming a mechanism from the clues on the page with the API 510 damage mechanism quiz.

What to record

• What was inspected, where, when, by whom and with which method.
• What you found, in plain terms, with location and size (a photo helps, a sketch helps more).
• Thickness readings with their locations, plus the rates, remaining life and next due date you calculated.
• What each finding means for the vessel's integrity, and what you recommend: monitor, repair, re-inspect sooner, evaluate or rerate.
• Open items from the last report and whether each is closed.
• Anything you could not inspect and why.

Write it so the next inspector can understand the vessel without calling you.

Where API 510 and RP 572 cover each item

Section numbers only. Read the text in your own copy, at the edition on the current effectivity sheet.

Checklist block	Where to read
Safety, preparation and inspection practices (external, internal, on-stream)	API 510 Section 5; RP 572 (its inspection practice and safety chapters)
How often each inspection is due, and when on-stream can replace internal	API 510 Section 6
Thickness readings, corrosion rates, remaining life	API 510 Section 7 (7.1, 7.2 and 7.4)
Records, reports and the permanent file	API 510 Section 7
Repairs, alterations and rerating	API 510 Section 8 (8.1 and 8.2)
Relief device checks	API RP 576
What the damage looks like and where it forms	API RP 571 (the paragraphs on your sheet)

The one-page version

Print this page and keep these on top.

☐	Before	On the walk	Before you leave
☐	Last report, readings and open items read	Foundation, supports, nozzles, insulation and relief device checked	Every finding located, sized and recorded
☐	Process changes and repair history known	Every leak and stain traced to a source	Readings entered with dates and locations
☐	Safety, isolation and entry permit confirmed	Internal surfaces cleaned first, then zone by zone	Rate, remaining life and next date worked out
☐	Instrument checked and locations marked	Welds, nozzle areas and low points given extra time	Recommendations and what you could not inspect written down

Where this shows up on the exam

Section IV of the Body of Knowledge covers inspection planning, repairs, rerating and pressure testing, and section V draws on RP 571 and RP 572. Many questions describe what an inspector found and ask what it means or what to do next. If you can go from a location to the likely mechanism to the method that finds it, those questions get easier. Pair this checklist with the Body of Knowledge guide, then check how you do on the free 10-question check.

Find your weak spot before the exam does

The free 10-question check takes a few minutes, needs no signup and explains every answer, so you see straight away whether inspection practice or the calculations need your time. The Long Seam course then adds a lesson for each Body of Knowledge domain, timed practice exams and a study plan built from your exam date.