Hastelloy Pressure Transducers

Pressure Measurement in Corrosive and Harsh Environments

By Core Sensors | December 10, 2022

When configuring a pressure transducer for your application, one question you will likely hear is: What is the media that will be making contact with the pressure transducer? While it may seem like a simple question, it is a very important one.

For the majority of applications that we encounter, 316L stainless steel is a fine choice. It is commonly used in applications requiring mild corrosion resistance such as water, oils, lubricants, utility grade natural gas, mild acids and hydrogen service. While 316L SS does offer a good deal of corrosion resistance, there are medias that will quickly corrode 316L SS, compromising the structural integrity of the pressure transducers diaphragm. In these applications, Core Sensors recommends Hastelloy C-276 superalloy.

What is Hastelloy C-276?

Hastelloy C-276 (UNS N10276) is a super nickel-molybdenum-chromium alloy offering high corrosion resistance in oxidizing and reducing environments. It exhibits excellent resistance to Sulfide Stress Cracking (SSC) and Stress Corrosion Cracking (SCC) due to the high molybdenum and chromium content, as well as the addition of 3.0-4.5% Tungsten.

Applications where Hastelloy pressure transducers are commonly recommended include:

Oil and Gas production – sour gas (high H2S content)
Seawater – exceptional crevice corrosion resistance
Pollution control – desulfurization systems
Wet chloride gas
Chemical processing plants
Hypochlorite

Hastelloy C-276 is a NACE MR0175/ISO 15156 compliant material for use in the oil and gas production industry.

Hastelloy C-276 Chemical Composition (%)

Nickel (Ni)	Balance
Molybdenum (Mo)	15.0-17.0
Chromium (Cr)	14.5 to 16.5
Iron (Fe)	4.0 to 7.0
Tungsten (W)	3.0 to 4.5
Cobalt (Co)	2.5 max
Manganese (Mn)	1.0 max
Copper (Cu)	0.5 max
Vanadium (V)	0.35 max
Silicon (Si)	0.08 max
Carbon (C)	0.01 max

Low Pressure Measurement in Corrosive Applications

Monitoring low pressures in corrosive applications is a difficult task due to the availability of corrosion resistant pressure transducers on the market. Two commonly recommended options for low pressure corrosive measurement are:

Diaphragm seals
- The Downside: In order to properly transmit pressure applied to the diaphragm seal, there needs to be enough displacement from the transfer fluid to the diaphragm of the pressure transducer. As a general rule of thumb, the smaller the pressure range, the larger the diaphragm seal needs to be. It is not uncommon to see a 1.5″ diaphragm seal for pressures below 15 PSI.
Ceramic diaphragms
- The Downside: While ceramic is highly corrosion resistant, an elastomer seal is required to attach it to the body of the pressure transducer. This elastomer is commonly overlooked when determining media compatibility. Incorrect compatibility with the elastomer seal can result in swelling, cracking and/or leaking of the process media.

Core Sensors’ Solution:

In an effort to simplify low pressure measurements in corrosive environments, Core Sensors offers Hastelloy C-276 material in a media isolated package. An oil filled sensor element is precision welded to the process connection threads without the use of O-rings or other sealing materials. This ensures that the corrosive media is only making contact with the materials used for the sensing element and threads. With this sensing method, Core Sensors is able to offer pressure ranges down to 1 PSI and up to 30 PSI in a small package; most commonly with 1/4″ Male NPT threads.

Core Sensors offers two types of material construction in low pressure designs:

Hastelloy C-276 diaphragm + 316L SS process connection threads
- With a thickness of 1 to 1.5 mils, the diaphragm is the thinnest component of the transducer. As a result, it is most susceptible to corroding in harsh environments. When working with medias that cause minor corrosion to standard austenitic stainless steels, selecting a Hastelloy C-276 diaphragm with 316L SS threads is an economical choice. The Hastelloy C-276 material will prevent the thin diaphragm from corroding and, while the 316L SS threads will show signs of surface corrosion, the structural integrity will remain intact.
- For applications where both corrosive media and clogging is a concern, Core Sensors offers a Hastelloy C-276 flush diaphragm with 1/2″ Male NPT threads in 316L SS.
All Hastelloy C-276 wetted material (diaphragm + process connection threads)
- When working with medias that are extremely corrosive to standard austenitic stainless steels, Core Sensors offers an all Hastelloy C-276 solution.

Process connection thread (left) and media isolated diaphragm (right).
Both available in 316L SS or Hastelloy C-276.

Single piece of Hastelloy C-276.
No oil filled diaphragms, O-rings or weld joints.

Medium to High Pressure Measurement in Corrosive Applications

For medium to high pressure applications, Core Sensors utilizes a high strength solid piece of Hastelloy C-276 which is free of fluid filled cavities, sealing materials such as o-rings, and weld joints. This solid piece of Hastelloy contains the corrosive media within the pressure port and reduces or completely eliminates the corrosion that is commonly seen when using standard austenitic stainless steels. For applications where standard tapered threads and Teflon tape are not desired, Core Sensors can offer straight threads (i.e. SAE 4) with a flare, creating a metal-to-metal seal and eliminating the need for an elastomer seal. Pressure ranges from 50 PSI up to 10,000 PSI are available.

Disclaimer: Core Sensors makes all reasonable efforts to ensure the accuracy of the information listed on this page. The above is for information only and should not be used as a sole source for application design. It is the responsibility of the end user to ensure that the intended material is the correct choice for that particular application. Conditions such as pressure, temperature, corrosiveness, environment (such as sour gas and concentration levels) and location around the world must be considered by the end user as part of the material selection.

For more information or to request a quote, please call us at 862-245-2673 or email [email protected].

*Hastelloy® is a registered trademark of Haynes International, Inc.

About Core Sensors:
Core Sensors designs, manufactures and distributes high quality sensors for measuring pressure and temperature properties for industrial and hazardous applications worldwide. Core offers solutions for industrial, submersible, differential and hazardous applications in both standard and custom packaging. In-house design and manufacturing capabilities along with strategic manufacturing partners allows Core to create solutions to some of the most complex sensor requirements.