Welding inspector certifications compared: AWS CWI, API 510, 570 and 577, and ASNT NDT
Which inspector certification fits which job
Pick the credential that matches the work you want to inspect. AWS CWI covers inspecting welds against a welding code, in structural, pipeline, bridge, aerospace and pressure work. API 510 (pressure vessels) and API 570 (in-service piping) are for inspecting equipment that is already in service, and they need inspection experience with an authorized inspection agency. API 577 tests welding processes and metallurgy for petrochemical inspectors, and current API 510, 570 or 653 holders qualify for it automatically. ASNT NDT Level II qualifies you to run a nondestructive test method such as ultrasonic or radiographic testing yourself. Level III is the managing tier: writing procedures and training teams.
Every detail below comes from each issuing body's own website, read on 2026-10-01. Requirements and fees change, so check the issuer before you apply. Where an issuer page did not state a detail, the table says "See issuer" and links to it.
Side-by-side comparison
↔ Swipe to see prerequisites, exam format, renewal and employers
| Credential | Issuing body | What it certifies | Prerequisites | Exam format | Renewal cycle | Typical employers |
|---|---|---|---|---|---|---|
| AWS CWI (Certified Welding Inspector) | American Welding Society | Welding inspection knowledge: destructive and nondestructive testing, fabrication math, safety, metallurgy, welding symbols, WPS/PQR and welding fundamentals, plus use of a code book. | A vision test and qualifying education plus welding-based work experience: 1 year with a bachelor's in welding engineering or technology; 2 years with an associate or higher in engineering technology, engineering or physical science; 3 years with engineering or technical courses toward a welding bachelor's; 4 years with trade or vocational courses; 5 years with a high school diploma; 9 years with 8th grade; 12 years below that. | Three exams, 72% minimum on each. Part A: 150 questions, computer-based at Prometric centers. Part B: hands-on practical with AWS equipment plus 46 questions. Part C: open-book, 50 to 65 questions on one code book (for example AWS D1.1, API 1104 or ASME Section IX). | Valid 9 years, with renewal applications at years 3 and 6; at year 9, recertify by options that include the Part B exam or 80 professional development hours. | See issuer: aws.org CWI page |
| API 510 (Pressure Vessel Inspector) | American Petroleum Institute (Individual Certification Programs) | Knowledge of maintenance, inspection, repair and alteration of pressure vessels. | Pressure-vessel experience gained within the last 10 years with, or under contract to, an authorized inspection agency: 1 year of inspection work with a BS in engineering or technology (or 3+ years of technical military service); 2 years with an associate degree or certificate; 3 years with a high school diploma; 5 or more years with no formal education. | One 7.5-hour exam day at a test center: 170 questions (140 scored), 110 closed-book and 60 open-book, with code PDFs provided on screen for the open-book part. | 3-year term. Each cycle: at least 20% of time in pressure-vessel inspection and 24 continuing professional development hours; an online open-book quiz every 6 years. | Authorized inspection agencies; API ties the continuing-education hours to the petroleum and petrochemical industry. |
| API 570 (Piping Inspector) | American Petroleum Institute (Individual Certification Programs) | Knowledge of maintenance, inspection, alteration and repair of in-service metallic piping systems. | Same education-and-experience tiers as API 510 (1, 2, 3 or 5+ years), with the experience in in-service piping, gained within the last 10 years with an authorized inspection agency. | Same structure as API 510: a 7.5-hour day, 170 questions (140 scored), 110 closed-book and 60 open-book, in person at a test center. | 3-year term, with 20% inspection time and 24 CPD hours per cycle and an online quiz every 6 years. | Authorized inspection agencies; see issuer: api.org API 570 page |
| API 577 (Welding Inspection and Metallurgy) | American Petroleum Institute (Individual Certification Programs) | Knowledge of welding processes and metallurgy. | Automatic for current API 510, 570 or 653 holders. Otherwise any petrochemical-industry experience within the last 10 years: 1 year with a BS in engineering or technology; 2 years with a 2-year degree or certificate; 3 years with a high school diploma; 5 or more years with no formal education. | 3.25 hours, 110 questions (100 scored). No paper or reference materials allowed. Test center or remote proctoring. | 3-year term. API states employment verification is not currently required to recertify. | API names inspectors, welding engineers and metallurgists across the petrochemical industry as its audience. |
| ASNT NDT Level II | American Society for Nondestructive Testing (ASNT Certification Services) | Working independently as an NDT technician in a given method: performing inspections, documenting results. | Method-specific supervised NDT experience and training. Examples: ultrasonic (UT) or radiographic (RT) testing, 120 days in the method, 229 total NDT days and 12 days of training; visual testing (VT), 30 days, 58 days and 4 days. | Computer-based: a general exam (50 items, 2 hours) and a specific exam (40 items, 2 hours) per method. The program meets Recommended Practice SNT-TC-1A, and applicants must also pass their employer's practical exam. | Every 5 years, by application (at least 36 of the 60 months working in Level II functions) or by exam. | See issuer: asnt.org Level II page |
| ASNT NDT Level III | American Society for Nondestructive Testing (ASNT Certification Services) | NDT management: writing inspection procedures, managing operations, training teams, running internal certification programs. | NDT experience in the methods applied for: 12 months (252 days) with a 4-year engineering or physical science degree; 24 months with 2 years of such college study; 48 months with no college. | Computer-based multiple choice: the NDT Basic exam (135 items, 4 hours) and at least one method exam. | Every 5 years, by 25 points plus 36 months of Level III work per method, or by retaking the method exams. | See issuer: asnt.org Level III page |
What each one costs
- AWS CWI: $1,255 for AWS members, $1,520 for non-members for the initial exams; $2,000 / $2,265 with Part B training. Renewal at years 3 and 6 is $630 / $895 by work experience or $1,000 / $1,265 by exam. More detail on the CWI page.
- API 510, 570 and 577: the certification pages do not list fees; API publishes them on its schedules and fees page.
- ASNT NDT Level II: $740 member, $820 non-member per method for the initial general and specific exams (MT, PT, RT, UT or VT); $370 / $410 per add-on or retake exam.
- ASNT NDT Level III: $545 member, $625 non-member for the Basic exam; method exams $525 to $545 member, $605 to $625 non-member depending on the method.
Do you need a CWI before a pressure-vessel inspector job?
Not to sit for API 510. API's eligibility table for API 510 lists education and pressure-vessel experience only, and the experience has to come from work for, or under contract with, an authorized inspection agency within the last 10 years. An AWS CWI is not on that list. The two answer different questions: a CWI shows you can judge a weld against a welding code, while API 510 shows you know the inspection, repair and alteration rules for pressure vessels that are already in service.
If you are a welder now and want the pressure-vessel path, the API 510 table tells you how much inspection experience you need first. A CWI can be a way into the inspection work that builds that experience, and its Part C exam can be taken on ASME Section IX, the code that governs welder and procedure qualification for boilers and pressure vessels. See our ASME Section IX page for what that code covers.
AWS CWI or ASNT NDT Level II?
They certify different jobs. A CWI inspects welds and welding work against a code: procedures, joint preparation, the finished weld. An ASNT NDT Level II technician performs a specific test method, such as ultrasonic, radiographic, magnetic particle, liquid penetrant or visual testing, and documents the results. Level II is method by method: each method has its own experience, training and exam. ASNT's Level II program also requires the employer's own practical exam, so an employer is part of the process either way.
A rule of thumb from the table above: if the job posting names a welding code (AWS D1.1, API 1104, ASME Section IX), it is asking for weld inspection, which is CWI territory. If it names a test method (UT, RT, MT, PT), it is asking for NDT, which is the ASNT path.
Can you hold more than one?
Yes, and the issuers build some of the stacking in. API 577 is open automatically to current API 510, 570 and 653 holders. The AWS CWI Part C exam can be taken on API 1104 (pipelines) or ASME Section IX as well as AWS codes. Each credential keeps its own renewal clock, though: 9 years for CWI, 3 years for each API certification, 5 years for ASNT, so holding several means tracking several deadlines.
What to ask an employer before you pay for an exam
- Which code or standard governs the work you would inspect (a welding code, API 510 or 570, or an NDT procedure)?
- Which credential does the job actually name, and is it required at hire or within a set time?
- For NDT work: does the employer run its own written practice and practical exams?
- For API 510 or 570: does the employer count as an authorized inspection agency, so that your time there builds the qualifying experience?
- Will the employer pay exam fees or renewal costs?
Related pages
FAQ
Do I need an AWS CWI before I can become an API 510 pressure vessel inspector?
No. API's published eligibility table for API 510 lists combinations of education and pressure-vessel experience gained within the last 10 years with an authorized inspection agency. It does not list an AWS CWI as a requirement (api.org, as of 2026-10-01).
What is the difference between AWS CWI and ASNT NDT Level II?
AWS CWI certifies welding inspection knowledge: three exams on welding fundamentals, a hands-on practical, and an open-book code exam. ASNT NDT Level II certifies a technician to perform a specific nondestructive testing method (such as UT, RT, MT, PT or VT) independently, with method-specific experience and training hours and an employer practical exam.
How long are these certifications valid?
AWS CWI: 9 years, with renewal applications at years 3 and 6. API 510, 570 and 577: 3-year terms. ASNT NDT Level II and Level III: renewed every 5 years. All as stated on the issuers' own pages as of 2026-10-01.
Does holding API 510 or 570 help with API 577?
Yes. API states that a holder of a current API 510, 570 or 653 certification automatically qualifies to sit for API 577 (api.org, as of 2026-10-01).