How Do You Select Safe Pressure Instruments for Acid Applications?

Working with acids like hydrofluoric acid (HF) requires instrumentation designed to contain hazardous media and resist corrosion. Selecting the right pressure and temperature measurement solutions is essential to protect both personnel and equipment from acid leaks, instrument failures and hazardous chemical exposure.

While dangerous acids have been safely used in industrial applications for many years, specifying proper pressure instrumentation with the appropriate wetted materials for these locations, requires unique expertise. That's where Ashcroft can help. With decades of experience in pressure and temperature instrumentation for the process industry, we have guided customers to the information they need to ensure they are choosing the safest instrumentation for their acid application. 

Read this article to learn how to evaluate your instrument options and make informed decisions that improve safety, reliability and process containment for acid applications.

Why is instrument selection critical in acid applications?

Instrumentation must safely contain aggressive media while maintaining accuracy and reliability under harsh conditions. Improper selection can lead to corrosion, leaks, and potential safety incidents.

Acids such as hydrofluoric acid (HF) are widely used in processes like alkylation, where hydrocarbons are converted into high-octane fuel components. However, when released, HF forms dense vapor clouds that can cause severe burns and respiratory damage, making containment a top priority.

What are the primary safety concerns in acid applications?

The main safety concerns are elevated temperature, leak paths and material compatibility. Each of these issues directly impact instrument performance and process safety:

• Elevated temperatures can accelerate corrosion and degrade materials, reducing instrument life and reliability.

• Potential hazardous acid leak paths can come from small failures in the following areas:
  • Welds between components
  • Diaphragm seals
  • Gauge-to-seal connections
  • Internal sensing elements
    
    

• Materials that are not chemically compatible with the process media can corrode quickly, leading to instrument failure and unsafe conditions.

How can you detect acid leaks quickly and effectively?

Visual leak detection provides immediate indication of process failure, allowing operators to respond before conditions escalate.

One approach is using an acid leak detection (ALD) gauge and diaphragm seal assembly, which incorporates a coating that changes color when exposed to acids (pH ≤ 3.0). This visual indicator helps identify leaks at critical points such as welds and sensing elements. 

Figure 1. ALD Assembly

ALD features that improve leak detection and containment

• Visual color-change indication for fast response

• Dual containment design for added safety

• Compatibility with high-pressure applications (up to 10,000 psi)

• Optional fill fluids for oxidizing acids
• These features support safer operation in highly hazardous environments

ALD is available in orange or yellow gauge cases for easy identification. It is also available with Halocarbon® fill for oxidizing acids and silicone-free PLUS!™ Performance.  Read our CASE Study to see how ALD offered a solution to a challenging HF application. 

Why is material selection critical for acid applications?

Material selection is critical because acid exposure can quickly degrade incompatible materials, leading to corrosion, leaks and instrument failure.

In acid applications, wetted materials must be carefully selected to withstand aggressive chemical conditions. Many commonly used materials are not compatible with strong acids, making proper selection essential for safe and reliable operation.

Diaphragm seals require particular attention. Their diaphragms are intentionally thin to allow enough movement (displacement) to accurately transmit pressure to the instrument. However, this thin design also makes them more susceptible to damage from harsh conditions such as corrosion, erosion, and pitting.

Using thicker materials would reduce sensitivity and impact performance, so the solution is not added thickness, but selecting highly resistant materials that can prevent permeation or failure while maintaining accuracy.

What materials should or should not be considered for acid applications? 

• Hastelloy® and Tantalum materials are often selected for diaphragm seals and wetted components because of their strong corrosion resistance in aggressive acids.

• Monel® offers resistance to HF but may only provide single containment in some configurations. 

• Stainless steel can corrode in many acid environments, making it unsuitable for these applications. 

If you need to identify what materials are best for your application, you can use the Ashcroft® Material Selector tool for guidance.  

Why secondary containment is important for acid instrumentation?

Secondary containment helps prevent leaks from escaping the instrument, reducing risk to personnel and equipment.

A welded instrument assembly can provide this added protection by eliminating potential leak paths and improving overall system integrity. Using compatible materials across all components is essential when welding accessories like snubbers to reduce pulsation, isolators to protect sensing elements and temperature dissipaters to reduce heat. 

These devices can be used alongside diaphragm seals and leak detection solutions to improve reliability.

Ready to learn more about instruments for acid applications?

Safe instrumentation selection comes down to material compatibility, containment and early leak detection. Contact us if you have questions or review the related content below to learn more. 

In the meantime, download our guide to see the solutions we offer for harsh chemical environments.