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ASME OM Code Cases-2015 — OM Code Cases (For Division 1)
🏭 The ASME OM Code Cases (2015 compilation) collects all currently effective OMN-series code cases issued by the ASME Operation and Maintenance Committee for Division 1 of the OM Code (Operation and Maintenance of Nuclear Power Plants). A Code Case is the official method of handling a reply to an inquiry: when study indicates that the Code wording needs clarification, when the reply modifies the existing requirements of the Code, or when it grants permission to use alternative methods, the Committee publishes the answer as a Code Case. Cases remain in effect for the applicable editions and addenda until they are annulled.
💡 Since July 2006 the Committee eliminated “expiration dates” for code cases: cases issued after that date carry no expiry and may be used as long as they are not annulled; older cases that have not been annulled and whose expiration date fell after July 2006 are likewise not expired and remain usable. Cases are published and updated on the ASME website under the OM Committee page.
1. Scope and Rules of Use 📌
The OM Code (Division 1) governs preservice and inservice testing (IST) and examination of safety-related pumps, valves, snubbers, and safety valves in nuclear power plants. Code cases serve three purposes: clarifying Code wording, modifying existing requirements, and approving alternative methods. When plants and regulators cite a case, it should be treated as a formal supplement to the Code text. Because the OM Code is the primary basis of the inservice testing programs required by the NRC’s plant technical specifications, the code cases that relax or refine those rules have direct regulatory significance for every operating light-water reactor.
- Effectiveness: a case remains in effect for the applicable editions and addenda until annulled; the latest revision of each case is listed individually, with all previous revisions incorporated into the latest revision.
- How to cite: reference the case number (e.g., OMN-13, Revision 2) and the applicable edition/addenda explicitly in the IST program or technical specifications.
- Regulatory acceptance: use must be compatible with the NRC or the applicable national regulatory framework; regulatory confirmation may be needed.
⚠️ A case is not a “permanent pass”: if a later Code edition formally incorporates the case content into the Code text, the case is typically disposed of accordingly. Always verify the current status and latest revision of the case before use.
2. Overview of the Code Cases 🔧
The 2015 compilation covers multiple topics of inservice testing and examination. The cases can be grouped by theme:
| Case No. | Topic | Main Content |
|---|---|---|
| OMN-1 (Rev 1) | Motor-operated valves (MOVs) | Alternative rules for inservice testing of active MOV assemblies in light-water reactor plants |
| OMN-3 / OMN-4 | Safety significance categorization | Safety significance categorization using risk insights; check-valve risk insights |
| OMN-6 | Digital instruments | Testing and calibration requirements for digital instruments |
| OMN-7 / OMN-11 / OMN-12 | Risk-insight extensions | Risk-insight methods for pump testing, MOVs, and pneumatically/hydraulically operated valves |
| OMN-8 | Control valves | Inservice testing requirements for control valves |
| OMN-9 / OMN-16 | Pump curve testing | Pump curve testing and alternative rules for using a pump curve in testing |
| OMN-10 | Safety-significance snubber testing | Testing of safety-significant snubbers |
| OMN-13 (Rev 2) / OMN-15 (Rev 2) | Snubber examination | Extending snubber visual examination and operational readiness testing intervals |
| OMN-17 | Class 1 pressure/safety valves | Alternative rules for Class 1 pressure/safety valves |
| OMN-18 / OMN-19 | Pump test limits | Alternative rules for pumps tested within ±20% of design flow; alternative upper limit for the comprehensive pump test |
| OMN-20 / OMN-21 | Test frequency and parameter adjustment | Inservice test frequency; alternative requirements for adjusting hydraulic parameters to specified reference points |
💡 Thematic thread: early cases focused on relaxing examination/testing requirements (e.g., extending snubber inspection intervals); later cases introduced “risk insights” methods that direct resources toward equipment of higher safety significance, reflecting a risk-informed approach to inservice testing.
3. Engineering Practice Essentials 🛠️
- 🔍 Case review: before citing a case, the IST engineer and the technical-specifications holder jointly review the applicability conditions, limitations, and record requirements.
- 📊 Risk categorization: when using OMN-3/4/7-type cases, retain the categorization rationale (safety significance, failure consequences, operating experience) for regulatory review.
- 📋 Records and reporting: record test data, deviations, and results per the case requirements; preserve trend data for pump curve and MOV tests.
- 🔄 IST program integration: case requirements must be written into the plant IST program and included in the quality assurance records system.
🚨 Note: when invoking alternative rules, the fundamental “must” requirements of the original Code paragraph still apply. A code case permits a specified deviation or an alternative method — it does not exempt the verification of safety functions. Anything not covered by the case is still executed per the OM Code text.
In practice, plants should treat the annual compilation like a living document: the OM Committee continues to approve new cases and revise existing ones in response to operating experience, component reliability data, and regulatory feedback. The compilation lists the latest revision of each case first, and all previous revisions are incorporated into that latest revision, so users should always cite the revision number in their IST procedures and maintain a cross-reference from the plant technical specification to the applicable case. This traceability matters because regulators typically review whether the credited case was in effect for the specific IST interval being reported.
Case-by-Case Application Notes
For motor-operated valves, OMN-1 historically allowed full-flow testing at reduced intervals or alternative diagnostic-based approaches; its successor rules are the basis of much of today’s MOV periodic verification. For check valves, risk-insight cases (OMN-4 and related) permit the owner to grade check valves by risk significance so that the testing effort is proportional to the actual contribution to safety. Pump-related cases (OMN-7, OMN-9, OMN-16, OMN-18, OMN-19, OMN-21) address the comprehensive pump test, the group test, and the use of pump curves with specified reference points; they also provide alternative upper limits and test-frequency adjustments when the pump cannot be tested at design flow. Safety-valve cases such as OMN-17 relax some of the Class 1 pressure/safety valve testing burden where service history justifies it. Each such relaxation must be justified in the plant’s IST program documentation with reference to the specific case text.
4. Frequently Asked Questions ❓
❓ Q: What is the difference between a Code Case and a formal Code paragraph?
A: A Code Case is the Committee’s official reply to an inquiry; within its defined scope it has the same binding effect as the Code, but it is published separately as a “case.” Formal paragraphs are incorporated into the Code body, and a case’s content may later be superseded by Code text.
A: A Code Case is the Committee’s official reply to an inquiry; within its defined scope it has the same binding effect as the Code, but it is published separately as a “case.” Formal paragraphs are incorporated into the Code body, and a case’s content may later be superseded by Code text.
❓ Q: Do code cases expire?
A: Cases published after July 2006 have no expiration date and remain valid unless annulled; earlier cases not annulled may also continue in use. Verify the case’s current status and latest revision on the ASME website before use.
A: Cases published after July 2006 have no expiration date and remain valid unless annulled; earlier cases not annulled may also continue in use. Verify the case’s current status and latest revision on the ASME website before use.
❓ Q: Are the risk-insight cases (OMN-3/4/7/11/12) mandatory?
A: No — they are alternative/enhancement paths. Plants may use conventional methods or risk-insight methods; choosing the risk-insight route requires completing the categorization justification and satisfying the case’s documented record requirements.
A: No — they are alternative/enhancement paths. Plants may use conventional methods or risk-insight methods; choosing the risk-insight route requires completing the categorization justification and satisfying the case’s documented record requirements.
🔍 Q: What is the basis for extending snubber inspection intervals in OMN-13/15?
A: Operating experience and failure statistics demonstrating that longer visual examination/operational readiness test intervals do not reduce the availability of safety functions; citing them requires meeting the case’s conditions on snubber type, service time, and historical performance.
A: Operating experience and failure statistics demonstrating that longer visual examination/operational readiness test intervals do not reduce the availability of safety functions; citing them requires meeting the case’s conditions on snubber type, service time, and historical performance.
