Fit-for-purpose control valves: lessons from a petrochemical audit
TL;DR: A control valve that "passes" a vendor's own sizing software may still be wrong for the application. Industry experience from petrochemical projects shows that a meaningful proportion of control valves in any given package are not genuinely fit for purpose, and that the problems only surface during commissioning - when fixing them is most expensive. An independent, multi-criteria sizing tool used systematically at the engineering stage catches these mismatches early. CONVAL 12, developed by F.I.R.S.T. GmbH, applies exactly this kind of structured, vendor-neutral analysis. This post explains why fitness-for-purpose audits matter and how calculation tools that are independent of any valve manufacturer support them.
Why "sized correctly" is not the same as "fit for purpose"
Most control valve sizing exercises begin and end with one question: does the Cv (or Kv) fall within the acceptable range for the selected valve body? If yes, the valve gets specified and ordered.
That one-question approach misses most of what can go wrong.
A valve can have the right Cv and still fail to control reliably because it operates in a region where valve gain is too high or too low. It can produce damaging cavitation at minimum flow even though the sizing calculation was carried out correctly. It can generate noise that breaches site limits at normal operating conditions that were never modelled. It can create reliability problems because a combination of physical parameters, none individually flagged, combine into a destructive condition across the full working range.
These are not edge cases. They are, according to Henk Hinssen, a retired instrumentation engineering associate with over 40 years in the petrochemical industry including 35 years with a major American oil and gas company, the ordinary failure modes of valve sizing and selection as practised on most projects (Hinssen, 2017). Valves are routinely specified with a single working point when the application requires at least three. The consequence is predictable: plants that reach commissioning with a subset of control valves unfit for their application, and startup teams spending weeks on corrections under schedule pressure.
What a fitness-for-purpose audit actually involves
The Texas A&M Instrumentation Symposium 2012 paper co-authored by Hinssen, together with Holger Siemers (retired valve supplier) and Andreas Vogt (F.I.R.S.T. GmbH), introduced a structured framework for thinking about control valve fitness-for-purpose during the sizing and selection phase (Hinssen, Siemers and Vogt, 2012).
The central contribution of that paper was the articulation of two key performance indicators, the Reliability Index (Ri) and the Controllability Index (Ci), and the case for evaluating them together rather than relying on Cv alone.
Reliability Index (Ri) is a predictive measure of how reliably a given valve and actuator configuration will perform across the full travel range of the application. Rather than reducing reliability to a single pass/fail flag at one operating point, Ri generates a curve across the valve's working range. That curve reveals where reliability challenges may emerge: at minimum flow, during startup, or at any intermediate condition the single-point sizing exercise never considered.
The index takes account of:
- Flow phenomena across the full working range, including cavitation, flashing, choked flow, and outgassing
- Physical parameter combinations such as pressure drop, outlet velocity, dissipated power, and noise, which can be individually acceptable but collectively problematic
- The contribution of valve class and material class to the overall reliability picture
Ri produces a traffic-light output: green means the valve is reliable across the control range of interest, yellow signals that the design should be revisited, and red indicates the selection should go back to the drawing board before purchase (Hinssen, Siemers and Vogt, 2012).
Controllability Index (Ci) addresses a related but distinct question: will the valve control well in the application for which it has been selected? Static controllability, meaning the relationship between valve travel and process gain across the operating range, is the focus. Ci is expressed as a curve over the full travel range and is calculated separately for follow-up control (where the valve must track a changing setpoint across a wide range), setpoint control (operation around a fixed setpoint), and startup control (where the valve must function stably at low flow before full production is established).
Together, Ri and Ci provide a picture of valve behaviour across the whole operating envelope rather than at the single nominal condition that dominates most datasheets.
Why vendor-independent calculation is the critical requirement
This is where the choice of tool matters.
A vendor's own sizing software is built to size valves from that vendor's catalogue. It will check whether a given body size meets the required Cv. It may flag obvious problems. But it has no structural reason to challenge the selection comprehensively, no incentive to weight reliability and controllability against alternatives from outside its own range, and no mechanism for calculating phenomena such as Ri and Ci that were developed specifically to overcome the limitations of single-criterion sizing.
Hinssen makes this point explicitly. In a 2014 column for Valve World Americas, he described his years as an NPQC engineer at EPC offices, trying to spot design flaws in instrument datasheets and valve indexes. He characterised the challenge as "like trying to find a needle in a haystack" when using conventional tools, and traced his own journey towards a vendor-independent commercial sizing tool as the critical step that changed his ability to address reliability and controllability challenges across a complete dataset of valves, not just one at a time (Hinssen, 2014).
That journey eventually led him to work with F.I.R.S.T. GmbH to develop the CONVAL Adapter Tool (CAT), a batch-mode capability that can ingest a full instrument index from project engineering tools such as SmartPlant Instrumentation (SPI) and automatically identify which valves in the dataset are not fit for purpose, so they can be redesigned before purchase.
The benefit/cost ratio Hinssen cites for this kind of pre-purchase audit is more than 100 to 1, achieved not by reducing engineering hours but by avoiding the capital expenditure required to correct design flaws during commissioning and startup (Hinssen, 2017). A valve body that is wrong for its application and is discovered during startup may require full replacement: the correct body, trim, actuator and accessories re-engineered, expedited, and installed under schedule pressure. Catching the same issue at the FEED or detailed engineering stage costs a recalculation and a revised datasheet.
What CONVAL 12 brings to a fit-for-purpose audit
CONVAL 12, developed by F.I.R.S.T. GmbH, implements the Ri and Ci methodology directly. Several features are specifically relevant to fit-for-purpose auditing.
Multi-point working range analysis. CONVAL 12 accepts multiple operating points for a single valve, evaluating cavitation risk, noise, outlet velocity, and control performance across the full range of process conditions. Adding minimum and startup flow conditions beyond the maximum-flow datasheet point substantially changes the reliability picture, as the 2012 Texas A&M paper demonstrated.
Ri traffic-light visualisation. The reliability curve plots Ri as a function of flow or valve travel. Problem zones appear visually, together with the specific reliability sub-issue and a recommended mitigation: a different valve class, material class, or trim type. The output is actionable in an engineering review, not merely a number to file.
Ci over the full control range. The controllability curve allows the engineer to assess stable control across follow-up, setpoint, and startup modes. Where Ci falls outside acceptable limits, the tool identifies where in the travel range the problem occurs.
Batch audit capability. Through the CONVAL Adapter Tool, a complete project instrument index can be processed in batch mode, automatically flagging valves below acceptable Ri or Ci thresholds. For a project with hundreds of control valves, this transforms the audit from a needle-in-haystack exercise into a structured review of a prioritised exception list.
Manufacturer independence. CONVAL calculates against published standards including IEC 60534, ISA 75.01, and VDI/VDE 2173. The results are the same regardless of which manufacturer's data are entered. A vendor's own software might return a comfortable result for that vendor's product; CONVAL returns a result based on the physics and the standards.
Applying the audit approach: what to look for
Drawing on the methodology set out in the 2012 Texas A&M paper, a fit-for-purpose audit conducted with CONVAL involves several disciplines that single-point sizing exercises routinely skip.
Use at least three working points. Minimum flow, normal flow, and maximum flow are the baseline; startup conditions should be added where the application warrants it. A valve that looks acceptable at maximum flow may cavitate destructively at minimum flow or fail to control in a stable maner during startup.
Check the full phenomenon set. Cavitation, flashing, choked flow, and outgassing each behave differently across the operating range. CONVAL models all of them and plots behaviour as a function of flow and travel, identifying conditions that a single-point calculation would miss entirely.
Review physical parameter combinations. Outlet velocity, pressure drop, dissipated power, and noise all contribute to reliability. Any of these individually may be within limits; it is their combination that creates the worst reliability outcomes. The Ri subclass structure within CONVAL captures this by assigning weighted contributions to each parameter and combining them into a single curve.
Classify your valve population by criticality. Hinssen's former organisation identified "High Performance" control valves at less than 10 per cent of the total population as those carrying disproportionate process risk. These receive the deepest analysis; the remainder are reviewed at a lighter level. CONVAL's batch audit capability supports this triage by screening the full population automatically and escalating high-risk cases for manual review.
The vendor-independence argument in practice
One of the more uncomfortable findings from any systematic fit-for-purpose audit is that valves which fail the independent analysis have often already been sized using the manufacturer's own software and flagged as acceptable.
This is not necessarily dishonesty on the vendor's part. Their sizing tools are designed to confirm that a product from their catalogue meets the primary criterion, which is Cv. Ri and Ci require methodology that is standardised and shared across the industry, not proprietary to any supplier; they emerged from end-user and industry collaboration, not from any single manufacturer's R&D department.
Hinssen's account of persuading his organisation to adopt a vendor-independent tool after almost 30 years is instructive. Half his colleagues resisted, perceiving the independent tool as more complex than the vendor software they were used to. The other half embraced it immediately. When the whole organisation finally adopted it, engineers were able to address control valve reliability during the FEED stage: identifying the High Performance valves early enough to secure the appropriate budget for them, rather than discovering the mismatch under commissioning pressure (Hinssen, 2017).
A fit-for-purpose audit with CONVAL 12 is not a rejection of vendor expertise. It is the application of independent, standards-based analysis to verify that the selected valve will do the job across its real operating range, with a structured record of the basis for that conclusion.
Summary
Control valve fit-for-purpose is a multi-criteria problem. Single-point Cv calculations address one criterion, at one operating condition, using one manufacturer's product data. That is not sufficient to confirm that a valve will perform reliably and controllably across its real service range.
The Ri and Ci methodology documented in the Texas A&M 2012 Instrumentation Symposium proceedings provides a structured framework for fit-for-purpose assessment at the engineering phase. CONVAL 12 implements that methodology: multi-point analysis, actionable reliability and controllability visualisations across the operating range, and batch processing of complete valve datasets to make project-scale audits practical.
The return is substantial. Corrections before purchase cost a recalculation. Corrections during commissioning cost weeks of delay, expedited fabrication, and the commercial and reputational consequences of holding up a plant startup.
DP-Flow supplies and supports CONVAL 12 in the UK and Ireland. For enquiries about how CONVAL can support control valve fit-for-purpose audits on your project, contact the DP-Flow team.
References
Hinssen, H. (2009) 'Optimierte Auslegung und Auswahl von Ventilen mit einem Regelgüteindex / Optimized design and selection of valves using a regulation quality index', Industriearmaturen, Heft 3/2009, September. Vulkan-Verlag GmbH, Essen.
Hinssen, H., Siemers, H. and Vogt, A. (2012) 'Key Performance Indicators for spotting the best Fit for Purpose Control Valve', Texas A&M Instrumentation Symposium 2012, 26 January 2012. [Conference presentation, copy held in DP-Flow/F.I.R.S.T. GmbH content library. No public URL available at time of writing; accessed June 2026.]
Hinssen, H. (2014) 'A new CAT on the NPQC scene!', Valve World Americas, May 2014, pp. 16. Available in DP-Flow/F.I.R.S.T. GmbH content library; accessed June 2026.
Hinssen, H. (2017) 'Catching unfit control valves', Control Valves [Valve World feature], April 2017, iHandl Engineering. [Copy held in DP-Flow/F.I.R.S.T. GmbH content library; accessed June 2026.]
F.I.R.S.T. GmbH (2025) CONVAL 12 - Instrument and Process Design Tool. Available at: https://conval.de/en [Accessed: June 2026].
Patrascioiu, C. and Stamatescu, G. (n.d.) 'Using the CONVAL® software for the petrochemical plant control valves checking'. Available from the publisher [Accessed: June 2026].