Stem sealing technology has evolved fast over the last 20 years. In the past methane emissions under 10,000 ppm were not recognised as potential leaks. Nowadays, methane emission levels lower than 100 ppm must be achieved to qualify as a low-emission solution.
Article By Ralf Vogel
This rapid change has been driven by legislation. Due to the climate change agreement, methane emissions (see box text, Dark horse,) from plants are regulated in the US and the EU is working on a program to reduce these emissions to lower levels before 2030. Also, legislation like the Industrial Emissions Directive 2010/75/EU helps to improve plant emissions further.
Beside legislation, industry standards work to regulate and qualify valves or valve stem solutions.
Here standards like ISO 15848-1 for valve classification or API 622 for the qualification of valve packings are important to drive developments further. This has been achieved by improving valve stem sealing technology as well as the design of valves.
Combined with better training for installers and maintenance personnel at end-users, emission levels and operational performance of valves have improved. Also, the safety and longevity of the solutions i.e., by life loading the gland, have been increased.
Another challenge for valves and valve stem sealing solutions are new developments regarding alternative energy generation. Hydrogen comes to mind, an energy carrier which requires ultra-low temperatures. There are also improvements in the energy efficiency of power stations where the steam temperatures are raised further up to 750 °C. For these extremes new materials and solutions must be developed. Expanded graphite with oxidation inhibitors or spacer discs for oxidation protecting of graphite packings, made from vermiculite or boron nitride, are some of them.
In the following articles different aspects of these valve seal developments are covered. From special polymer spring-energised seals for critical valve applications to the use of graphite packing at low temperatures in contact with liquid hydrogen. Also, factors that can negatively influence the packing performance like valve stem corrosion. The last paper reflects on valve stem sealing standards and discusses their advantages and disadvantages.
Valve stem technology
Two of the four articles in this series have been writ ten by ESA (European Sealing Association) members.
The ESA represents most European sealing manufacturers and aims to provide training and documentation about sealing solutions. Documents like “Sealing devices reduction of fugitive emissions document – Best available techniques” are used by the European Commission as a reference document for the update of BREF-documents.
Valve stem technology has evolved over the last years, driven by legislation and industry standards as well as a need to minimise emissions from plants further to reduce the effects of climate change. Still, efforts are made to improve a mature technology like packings even further to make valve applications better not only regarding emissions but also improving functionality by reducing friction and stress relaxation.