When KW Designed Solutions were asked by TWI to supply three high pressure testing systems for simulating downhole sour gas environments to be used in their new National Structural Integrity Research Centre (NSIRC), one of the key design challenges was how to safely monitor the operating pressure of the extremely corrosive media (hydrogen sulphide) within the autoclaves.

A good safe system of working will usually require dual diverse methods of pressure monitoring. This typically involves having both a mechanical (bourdon tube) pressure gauge and an electronic pressure transmitter/ transducer with a digital readout. While pressure transmitters can be sourced with suitable diaphragm materials for the environment, the same is not the case for pressure gauges.

To incorporate standard instrumentation in systems with aggressive media, the normal procedure would be to fit a media separator or chemical seal between the aggressive media and the delicate and often incompatible instrumentation. However, after an extensive product search, there does not appear to be any commercially available seals for operating conditions of 1700 bar up to 300°C with hastelloy wetted parts.

The only option was to use our in-house experience of incorporating media separation into pressure systems and design a special-purpose chemical seal. Standard chemical seals use a diaphragm to isolate aggressive media from the closed pressure monitoring environment, however, the size of the diaphragm required for a design pressure of 2000 bar would need a large housing to contain the pressure loading. To make a more compact unit, a bellows arrangement was designed into a much smaller unit with sufficient volume displacement for both the gauge and transmitter.

The completed assembly was proof tested to 3000 bar and certified in accordance with the PED and CE marked for compliance. The final chemical seal unit is extremely compact and can be easily incorporated into any high pressure system and comes calibrated with an integral gauge and transmitter.

Our skilled engineers successfully designed and produced a clean high pressure, high temperature testing environment, whilst using aggressive and dirty test media, simulating downhole sour gas environments, and delivering accurate and reliable test results.

Please follow the link below to see examples of our high pressure, high temperature autoclaves with integrated mechanical strain along with automated programmable pressure and temperature control systems, designed, manufactured, installed and commissioned at TWI’s Aggressive Environment Testing Facility.


High pressure, high temperature chemical seal


  • 1700 bar, maximum working pressure
  • 63mm or 100mm pressure gauge and integral pressure transmitter
  • Hydrogen Sulphide (H2S) – corrosive media separation
  • Media temperature up to 300°C
  • Standard high pressure autoclave connections
  • Wetted components manufactured from hastelloy C276


  • Fully certified and approved
  • Separation of corrosive media provides a clean and adequate interface for installation of standard components, e.g. pressure gauge, pressure transmitters
  • Separation provides a clean pressure control system for robust operation
  • HPHT autoclave systems for accurate downhole sour gas environment simulation (other autoclave system examples)
  • Accurate and reliable test data