SNT-TC-1A vs CP-189 — Which ASNT Standard Do You Need?

Introduction: Two Paths to NDT Personnel Qualification

In North America, most organizations qualify their NDT personnel using one of two ASNT documents: SNT-TC-1A (Recommended Practice) or CP-189 (Standard for Qualification and Certification). While both aim to ensure competent NDT personnel, they differ significantly in approach, prescriptiveness, and industry acceptance.

Choosing the right standard affects your audit outcomes, client acceptance, regulatory compliance, and the portability of your personnel certifications. This guide provides a detailed comparison to help you make an informed decision.

Overview: SNT-TC-1A

Full title: Recommended Practice No. SNT-TC-1A — Personnel Qualification and Certification in Nondestructive Testing

Type: Recommended practice (not a mandatory standard)

First published: 1966

Current edition: 2020

SNT-TC-1A is the most widely used NDT personnel qualification document in North America. As a "recommended practice," it provides guidelines that employers adapt through their own written practices. The employer retains significant flexibility in how they implement the recommendations.

Overview: CP-189

Full title: ASNT Standard CP-189 — Standard for Qualification and Certification of Nondestructive Testing Personnel

Type: National consensus standard (ANSI-approved)

First published: 1991

Current edition: 2020

CP-189 is a more prescriptive standard that mandates specific requirements rather than providing recommendations. It was developed to address industry concerns about inconsistent implementation of SNT-TC-1A across different employers.

Key Differences at a Glance

Feature	SNT-TC-1A	CP-189
Document type	Recommended practice	National standard (ANSI)
Language	"Should" (advisory)	"Shall" (mandatory)
Employer flexibility	High	Limited
Examination source	Employer-developed or ASNT	ASNT exams required
Written practice	Required, employer-customized	Required, must meet standard
Training documentation	Recommended	Mandatory with specific records
Certification portability	Employer-specific only	More portable (standardized exams)
Vision requirements	Near-vision acuity, annual	Near-vision acuity, annual + documented
Level III certification	Employer-administered exams	ASNT exams mandatory

Detailed Comparison

1. Examination Requirements

SNT-TC-1A: Requires general, specific, and practical examinations, but the employer develops or selects the exams. Exam content and passing criteria are determined by the employer's written practice.

CP-189: Requires ASNT-administered examinations for the general and specific portions. The employer may only develop the practical examination. This ensures consistent exam quality across organizations.

Impact: CP-189's use of standardized ASNT exams provides greater confidence in personnel competence and makes certifications more meaningful when reviewed by clients or auditors.

2. Training Requirements

SNT-TC-1A: Provides recommended training hours per method and level as guidelines. The employer may adjust these based on the candidate's education and experience. Training documentation is recommended but the format is flexible.

CP-189: Specifies mandatory minimum training hours that cannot be reduced. Training must be formally documented with instructor qualifications, course content, and attendance records.

3. Written Practice

Both documents require employers to maintain a written practice that documents their qualification program. However:

SNT-TC-1A: The written practice can deviate from the recommended practice as long as deviations are documented and justified. This provides flexibility but can lead to inconsistent implementation.

CP-189: The written practice must meet all mandatory requirements of the standard. Deviations are not permitted for mandatory ("shall") requirements.

4. Certification Records

SNT-TC-1A: Recommends maintaining certification records but provides limited guidance on format and content.

CP-189: Mandates specific certification record contents including training documentation, exam results, experience verification, vision test results, and authorized signature.

5. Recertification

SNT-TC-1A: Recommends recertification at intervals not to exceed 5 years for Level I and II, and 5 years for Level III. Recertification methods are flexible.

CP-189: Requires recertification at intervals not exceeding 5 years. Re-examination is mandatory—experience alone does not qualify for recertification.

Which Industries Require Which Standard?

Industries That Commonly Require CP-189

• Nuclear (ASME Section III, NQA-1): Many nuclear programs require CP-189 or equivalent due to its prescriptive nature and standardized exams
• Department of Defense: DoD specifications increasingly reference CP-189
• Critical infrastructure: High-consequence industries prefer the rigor of CP-189
• Clients with strict quality programs: Major EPC companies and asset owners may specify CP-189

Industries Where SNT-TC-1A Is Predominant

• Oil & Gas (API standards): API 510, 570, and 653 reference SNT-TC-1A as the default
• Petrochemical and refining: Most refineries accept SNT-TC-1A
• General manufacturing: ASME Section V references both, with SNT-TC-1A being more common
• Structural steel: AWS D1.1 references SNT-TC-1A

Standards That Reference Both

ASME Section V accepts both SNT-TC-1A and CP-189 for personnel qualification. The referencing construction code or client specification typically determines which is required.

Making the Right Choice for Your Organization

Choose SNT-TC-1A If:

• Your clients and industry codes accept it
• You need flexibility to tailor the program to your operations
• You have experienced Level III personnel to develop quality exams
• Cost and simplicity are priorities
• Your work is primarily in oil & gas, petrochemical, or general manufacturing

Choose CP-189 If:

• Your clients or regulatory environment require it
• You want standardized, defensible exams from ASNT
• You need certifications with greater portability
• You want to minimize audit findings related to personnel qualification
• You work in nuclear, defense, or high-consequence industries

Consider Implementing Both If:

• You serve diverse markets with different requirements
• You want to exceed minimum requirements for competitive advantage
• Your written practice can accommodate both frameworks

Common Audit Findings Related to Personnel Qualification

Regardless of which standard you choose, these are the most common audit findings:

• Written practice does not reflect actual practices
• Training records incomplete or missing
• Vision test not performed annually
• Certification expired without recertification
• Exam records not retained or incomplete
• Level III not properly qualified to certify Level I/II personnel
• NDT methods performed by personnel not certified in that method

How Atlantis NDT Can Help

Atlantis NDT provides Level III consulting services for personnel qualification programs under both SNT-TC-1A and CP-189:

• Written practice development and review
• Examination development and administration
• Qualification program audits and gap analysis
• Level III oversight for personnel certification
• Transition support from SNT-TC-1A to CP-189 (or vice versa)

Need the fundamentals first? See our SNT-TC-1A certification overview for what the employer-based model actually is and how it stacks up against CP-189, ISO 9712, ACCP, and Canada's CGSB-derived scheme.

Contact us for expert guidance on your NDT personnel qualification program.