SNT-TC-1A vs NAS 410: Which Standard Fits Your Team?
In the world of Non-Destructive Testing (NDT), ensuring personnel are properly qualified is paramount to safety and quality. Two of the most prominent documents governing this process in the United States are ASNT’s SNT-TC-1A and the Aerospace Industries Association’s (AIA) NAS 410. While both aim to standardize NDT training and certification, they are fundamentally different in their approach and application.
Choosing the right standard is not just a matter of preference; it’s often dictated by contractual and industry requirements. Understanding the key differences in philosophy, stringency, and intended use is crucial for any organization that relies on NDT.
The Core Difference: “Should” vs. “Shall”
The most significant distinction lies in their core philosophy.
- SNT-TC-1A: A Recommended Practice. Developed by the American Society for Nondestructive Testing (ASNT), SNT-TC-1A provides guidelines for employers to create their own in-house, employer-based certification program.[1][2][3] The document frequently uses the word “should,” indicating that its recommendations can be modified by the employer to meet their specific needs, so long as these changes are documented in their “written practice.”[3][4] This flexibility allows it to be adapted across a wide range of industries, including oil and gas, power generation, and construction.[5]
- NAS 410: A National Standard. Evolving from the military standard MIL-STD-410, NAS 410 is a standard that establishes the minimum requirements for qualifying and certifying NDT personnel.[4][6][7] This document uses the word “shall,” making its requirements mandatory and less flexible. It is the go-to standard for the aerospace, defense, and aviation industries.[4][8] If you are performing NDT work for these sectors, adherence to NAS 410 is almost certainly a contractual obligation.[9]
Industry Application: Where Are They Used?
The choice between the two is primarily driven by the industry you serve.
- SNT-TC-1A is the most widely used framework for NDT certification in the United States across general industry.[5][10] Its adaptability makes it suitable for companies in transportation, construction, petrochemicals, and more.[5][11]
- NAS 410 is mandatory for companies involved in aerospace and defense manufacturing, service, maintenance, and overhaul.[6][7][8][12] Compliance is often a prerequisite for NADCAP (National Aerospace and Defense Contractors Accreditation Program) audits.[9]
Key Technical and Administrative Differences
Beyond philosophy, the standards differ in several critical requirements for personnel certification.
| Requirement | SNT-TC-1A (Recommended Practice) | NAS 410 (Mandatory Standard) |
| Written Program | Requires a “Written Practice” that can be adapted from SNT-TC-1A guidelines.[4][10] | Requires a “Certification Procedure” that must meet or exceed the minimum requirements of the standard.[5][13] |
| Training & Experience Hours | Provides recommended minimum hours. For example, to achieve Level II in Liquid Penetrant (PT), it recommends 12 additional hours of training and a total of 210 hours of experience.[9] | Mandates specific, often higher, minimum hours. For PT Level II, it requires 16 additional hours of training (for a total of 32) and a total of 400 hours of experience.[9][12][14] |
| Examinations | Recommends a composite score of 80% across general, specific, and practical exams.[10] | Requires a composite score of 80%, with a minimum of 70% on each exam. It also specifies a higher number of questions for the specific exam (30 vs. 20 for SNT-TC-1A).[5][9] |
| Recertification | Personnel typically require recertification every five years.[15] | Recertification is required every five years, but NAS 410 also mandates annual skills proficiency tests to be documented by the employer.[9][14] |
| Level III Qualification | Allows for the employer to certify their own Level III personnel based on experience and examinations. | While not mandatory, it allows the possession of a current ASNT NDT Level III certificate to be used as evidence for passing the general examination requirement.[6][16] |
Which Standard Fits Your Team?
Making the right choice is a straightforward process based on your business needs and client requirements.
Choose SNT-TC-1A if:
- Your work is in general industry, such as oil & gas, construction, or manufacturing, where aerospace or defense contracts are not a factor.
- You need the flexibility to adapt the qualification and certification program to your company’s specific applications and equipment.
- Your clients specify compliance with an employer-based NDT program based on ASNT’s recommended practices.
You must use NAS 410 if:
- You work in the aerospace, aviation, or defense industries.[4][8]
- Your contracts explicitly require compliance with NAS 410 or you are subject to NADCAP audits.[9][12]
- Your clients demand a more stringent, standardized approach to NDT personnel qualification that meets established minimums rather than flexible guidelines.
In some cases, companies that serve a diverse range of industries may need to maintain a quality system that can satisfy both standards, which can be complex.[9] For many, this may even mean maintaining two separate written practices to ensure compliance during audits. Ultimately, the decision is guided by your contractual obligations and the industry you serve, ensuring your team is qualified, certified, and ready for the job at hand.
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