At Ashcroft, we understand the danger of acid leaks.

That is why we have developed the Acid Leak Detection (ALD) assemble. ALD is a special yellow coating that changes to red once it is exposed to acids with a pH of ≤ 3.0, providing visual indication of a leak of process media.

For years, our CASE team has helped customers troubleshoot critical applications such as HF Alky. While dangerous acids have been safely used in industrial applications for many years, specifying proper pressure instrumentation for these locations requires unique expertise.

HF Alky Case Study

Products: Media corroding Monel gauge system

Failure Mode: HF Alky (hydrofluoric acid)

Operating Pressure: 60,100, 300 & 600 psi.

The Problem:

Hydrogen Flouride (HF) is used as a catalyst in the alkylation process – taking short chain olefins (propylene/butylene) and combining with isobutene (all gasses) into larger molecules suitable for motor fuels. This “Alkylate” is used as a blending stock for high octane gasolines. When released in the atmosphere. HF rapidly forms dense vapor clouds that can cause severe burns and injuries to eyes, nose, throat and respiratory system. Therefore, process containment is vital. While Monel offers acceptable resistance to HF, the gauge alone provides only single containment of the process media. Several refineries have contacted our CASE team to mitigate this issue. In our most recent case study, we have helped a refinery identify a double containment solution.

The Solutions:

The CASE team specified a 510 Monel diaphragm seal welded to a Duragauge Pressure Gauge. The assembly was heat treated to reduce the risk of stress corrosion cracking in HF Alky. A diaphragm seal also provides double containment. To visually differentiate these assemblies, the gauge dials were marked “For use in HF Alky Only”.
Additionally, to provide further protection to plant operators, the ALD assembly was recommended. The diaphragm seal is coated with a yellow acid detection paint. If acid should escape from the seal, it will turn red. The lower portion of the gauge is also coated with ALD to indicate any leakage in the bourdon tube or welded joints of the gauge system.


  • Acid sensing component (yellow in photo turns red when exposed to acid with a pH ≤ 3.0)
  • Dual containment for safety
  • Available with pressure ranges to 10,000 psi
  • Gauge welded to seal standard
  • Available with Halocarbon fill for oxidizing acids
  • Optional orange or yellow gauge case for identification
  • Available with Silicone-free PLUS! Performance
  • Custom dials available



Accuracy: ± 1.0% of span (1259, 1279) or ± 1.5% of span (16500)

Process Connection Size: 1/2NPT

Case Style:  Solid front with pressure relief back

Pointer: Micrometer, adjustable, aluminum

Weather Protection: Hermetically sealed: IP66

Diaphragm Seal Type: 510 Threaded, Df Flanged

Window Material: Shatterproof glass, acrylic (OPT.)

Tamper Proof Design: Diaphragm seal welded to gauge socket

Pressure Rating (MAWP):  Vac. To 1,500 psi @ 100°F (STD)
1,500 to 10,000 psi @ 100°F (OPT)


Diaphragm:  316L SS, Hastelloy C-276, Monel

Lower Housing (510 only): 316L SS, Hastelloy C-276, Monel


Top Housing: 316L SS, Monel (510 Only)