Replacing obsolete nuclear pressure transmitters: alternatives to discontinued Rosemount, Ametek, Foxboro, and ABB/Bailey models and older analog models 

Obsolescence in instrumentation and control (I&C) cannot be avoided. According to a report produced by Oak Ridge National Laboratory (ORNL) for the U.S. Department of Energy, more than 70% of electronic components are obsolete even before the system is first installed. Obsolescence therefore begins at commissioning, and worsens as the plant ages.

For a pressure transmitter, several factors compound one another:

• Scarcity of spare parts. Stocks run down, and the price of remaining parts rises.
• Loss of manufacturer support. When a supplier drops a product line, expertise and documentation become difficult to obtain.
• Loss of skills. Specialists able to work on older technologies are becoming harder to find and retain.
• Pressure from plant life extension. Operating programmes beyond 40 years require ageing to be managed over the long term — an issue IRSN sets out explicitly in its ageing management approach.

These factors carry a cost, and it is routinely underestimated. The ORNL report identifies several escalation drivers: premiums on spare parts and on support for legacy systems, reverse-engineering costs when the original supplier abandons a line, and the development of equivalencies for outdated designs. A straight-line projection of current spending therefore understates the real burden ahead.

A useful benchmark on volume: a nuclear unit typically relies on 400 to 600 pressure and differential pressure transmitters. At that scale, a widely deployed reference becomes an availability risk, not a one-off replacement.

There is also a scheduling constraint that nobody can compress. Nuclear-qualified instruments carry long lead times, and intervention windows are set by plant outages planned years in advance. A decision deferred by one quarter can translate into a delay of several years — or into a derogation that will have to be justified.

Fuji Electric France supports this type of challenge, from plants under construction to facilities undergoing refurbishment and decommissioning projects —see our instrumentation solutions for the nuclear industry.

Certain families appear regularly in obsolescence files, because they were deployed in large numbers between the 1970s and the 1990s:

• Rosemount 1150 series — 1151, 1152, 1153, 1154 — and their associated accessories
• Ametek / Gulton-Statham
• Foxboro N-E Series
• ABB and Bailey, depending on the series
• SMAR LD Series
• Legacy Weed / Ultra models
• 10-50 mA analogue loops, still in service but little supported by current manufacturers

This list is there to identify the tags worth examining, not to draw conclusions. The status of any given reference rests with the original manufacturer, and with them alone: a range may be fully discontinued, partly discontinued model by model, or simply moved into a maintenance phase with no further development. Fuji Electric does not comment on the lifecycle status of other manufacturers' products.

Where to verify the actual status of a reference ?

This is the step most often skipped, and the one that avoids the most unnecessary expenditure.

Three levels of reliability, from highest to lowest. The manufacturer’s official end-of-sales notices, including the latest order dates, are considered authoritative. Next come the manufacturer’s product pages and product lifecycle guides. Finally, there are catalogs from distributors, surplus dealers, and third-party marketing materials, whose obsolescence statements are unverifiable and sometimes inaccurate—none of which are sufficient to justify a technical modification.

Two caveats should be noted regarding this ranking.

Inclusion in the catalog does not prove that a product is currently in production. A product line may remain listed—with a technical data sheet to support it—even though production has ceased and only the listing remains. The only reliable proof is a written commitment from the supplier regarding availability and lead time for the exact configuration of your part number.

Manufacturers think in phases, not in black-and-white terms. Several manufacturers publish a four-stage lifecycle model—active, maintenance, limited support, obsolete—each involving a different level of service. This is the case with ABB, whose model is publicly available. This gradation provides information about timing: a product in the maintenance phase does not require immediate action, while one in the limited support phase requires planning. This is precisely what makes it possible to spread out replacements over several unit outages rather than having to handle everything at once.

There is no universally correct answer. Both technologies have their place, and the choice is made tag by tag.

Sticking with analog technology is justified when continuity is paramount: simple architecture, proven reliability, direct maintenance, and no embedded firmware. Analog technology minimizes changes to operating procedures and qualification dossiers, and reduces exposure to cybersecurity requirements and software-induced common-cause failures. It is often the most cost-effective option in terms of total cost for non-safety-related applications. Our analogue nuclear pressure transmitters certified to RCC-E meet this need.

Moving to digital makes sense where the application draws real benefit from it: a need for onboard diagnostics, remote configuration, higher accuracy or rangeability, integration into a modernised control architecture, or where the refurbishment project already involves a broader I&C overhaul.

What digital adds must nonetheless be accepted: cybersecurity requirements, firmware management over time, consideration of software common-cause failure, staff training, revised procedures, potential licensing impacts, and shorter product lifecycles. The ORNL report documents these constraints.

So the right question is not “analog or digital?” in absolute terms, but rather: Which technology is best suited for this specific application, given its safety class, its environment, and the impact on the entire life cycle?

Faced with an obsolete transmitter, four routes exist. They are not mutually exclusive: a mixed installed base often combines several of them.

1. Repair or refurbish existing equipment. Buys time in the short term. It does not resolve the underlying obsolescence and depends on parts availability.
2. Surplus stock or lifetime buy. Purchasing in one go the volume needed for the remaining operating life. Useful, but it ties up capital and requires qualified storage.
3. Premium qualified transmitter. Appropriate for the most demanding applications — safety-related duties, severe environments. Sometimes over-specified, and expensive, on tags that do not require it.
4. Functionally equivalent alternative. Selecting a new, properly qualified transmitter whose characteristics match the tag: analogue to preserve continuity, or digital where the application justifies it. This route limits engineering change and over-qualification, provided the equivalency is documented.

To these four routes should be added a preliminary option that is too often overlooked: replacing nothing. If the reference is still supported, continuing to operate it with an adapted maintenance plan remains the most economical solution. This is why status verification always precedes the choice of route.

A replacement is never chosen on the model number alone. The points to check, tag by tag:

• Measurement type: differential (DP), gauge (GP), or absolute (AP)
• Calibrated range and actual calibration points
• Output signal: 4–20 mA or 10–50 mA
• Process connection and electrical connection
• Envelope dimensions and mounting bracket compatibility
• Environmental conditions: temperature, seismic resistance, radiation exposure
• Safety class: safety, non-safety, safety-critical
• Accuracy, drift, response time
• Quality documentation and equivalency support
• Lifecycle and long-term availability

Lifecycle and long-term availability 6 essential criteria for ensuring a safety function using a pressure transmitter.

What decision path should you follow?

Always in this order: (1) identify the tag and verify the actual status of the reference, (2) analyse the application, (3) determine the risk class, (4) choose the replacement route, (5) assemble the evidence package, (6) select the supplier. Short-cutting status verification or application analysis is the leading source of error.

⚠️ Do not replace based solely on the part number
Two instruments from the same family may differ in their range, configuration, connections, materials, assembly, and qualification level. The decision must be based on the complete model code, the technical data sheet, the nameplate, and the application requirements.

What does a replacement really cost?

The purchase price is only part of the outlay. Engineering change, qualification, outage impact and maintenance all have to be added. The ORNL report gives an order of magnitude for the associated engineering and licensing evaluations $50,000 to $100,000 for a low-complexity case, $250,000 to several million for a medium-complexity case, and more beyond that. In many situations, the engineering change costs more than the components.

This is the decisive argument in favor of a well-chosen equivalence: it minimises engineering change, requalification and documentary impact.

What evidence should you gather before deciding?

For each tag: datasheet and complete model code; manufacturer evidence of lifecycle status, together with a written commitment on availability and lead time; qualification file (RCC-E, K3 / K3-ad as applicable); seismic and radiation withstand; electromagnetic compatibility; quality assurance and traceability; long-term availability data; supply chain robustness; and operating references in comparable environments.

This package protects safety and budget alike. It heads off the unwelcome surprises that arise during requalification, when they cost the most.

These transmitters also cover level measurement by hydrostatic pressure and flow measurement by ΔP across a primary flow element. The associated accessories — 2, 3 or 5 way manifolds, nuclear-grade electrical connectors, mounting brackets, HP/LP process connection switching devices and local digital indicators — ease adaptation to an existing installation.

Qualifications: RCC-E (NC) compliance, 2019 edition, including seismic performance (TAS); K3-A/1E and K3-ad/1E qualifications; component seismic spectrum up to 35G, radiation qualification TID 50 kGy with integrity up to 65 kGy, performance maintained under accident conditions (LOCA, high temperatures), ANFL-qualified electronics per IEC 62671, safety SIL2 / SIL3 in accordance with IEC 61508 and 61511, EDF and Framatome qualifications (QN100 / QN200 / QN300), and quality management systems compliant with ISO 19443, ISO 9001, and ISO 14001.

Fuji Electric does not promise a universal drop-in replacement and does not claim equivalency without evidence. The approach is a tag-by-tag technical review, with qualified alternatives proposed where the documentation supports them — including where the conclusion is that no replacement is needed for the time being. Full details of references and connections are on the the pressure transmitter nuclear product line.

You do not need a complete file to begin the analysis. One reference, a tag list or a datasheet is enough.

Send us your part number, tag list, or technical data sheet. Our experts will provide you with an initial technical assessment: what actually needs to be replaced, what can wait, points to watch out for, the information you’ll need to gather, and the simplest approach for your situation—analog equivalent, controlled digital migration, or a custom solution. All of this before you commit to a consultation or a modification.