Flow measurement for corrosive or hostile process liquids (strong acids and alkalis): which instrument is most suitable for accurate, reliable flow rate indication without intrusive pressure drop or corrosion issues?

Introduction / Context:
In chemical process industries, many lines carry highly corrosive liquids such as strong acids and alkalis. Selecting the correct flow meter is crucial for safety, reliability, and lifecycle cost. This question evaluates understanding of flow meter principles and materials compatibility, with emphasis on non-intrusive measurement and minimal maintenance in aggressive services.

Given Data / Assumptions:

• Process fluid: hostile/corrosive (e.g., HCl, NaOH, H2SO4).
• Objective: continuous flow rate measurement.
• Constraints: minimize corrosion, avoid unnecessary pressure drop, and maintain accuracy.
• Assume the liquid is sufficiently conductive for electromagnetic measurement.

Concept / Approach:
A magnetic flow meter (electromagnetic type) measures volumetric flow using Faraday’s law. It has no flow obstruction (full-bore liner with electrodes) and no moving parts. The wetted liner (PTFE, PFA, rubber) and electrode materials (Hastelloy, tantalum, titanium) can be selected to resist severe corrosion. Because it is non-differential-pressure-based and full bore, it imposes negligible permanent pressure loss and is ideal for slurries or dirty fluids as well.

Step-by-Step Solution:
Match meter principle to corrosive service: select non-intrusive, no moving parts.Check fluid property: most corrosive aqueous acids/alkalis are conductive, so magmeters work well.Confirm benefits: corrosion-resistant liners/electrodes and negligible pressure drop → magnetic flow meter chosen.

Verification / Alternative check:
Compare with differential-pressure devices (orifice, venturi): they require throat plates or converging sections and cause pressure loss. Materials/coatings must survive corrosion, increasing cost; build-up can alter calibration. Hot-wire anemometers suit gases and clean lab flows, not harsh liquids. Thus the magnetic meter remains most suitable.

Why Other Options Are Wrong:
Orificemeter: Creates permanent pressure loss; plate erosion/fouling risk in corrosive streams.Hot-wire anemometer: Typically for gases in research settings, not corrosive liquids.Venturimeter: Lower loss than orifice but still intrusive; corrosion and scaling concerns remain.Ultrasonic Doppler meter: Can work on some dirty liquids but often requires particulates/bubbles; materials and lining considerations remain and accuracy varies with profile and solids.

Common Pitfalls:
Assuming any DP meter is fine if built from exotic alloys; overlooking maintenance and drift from fouling; forgetting that magmeters require conductive liquids (not suitable for pure hydrocarbons or deionized water without conductivity enhancers).

Final Answer:
Magnetic flow meter