ASCO Solenoid Valves & Sour Gas Environments
Published 01 Mar 2017
This article has been written to provide information and guidance on the problems and risks associated when using some types of alloys in sour gas environments and the selection and specification of ASCO solenoid valves.
The article focuses on selection of materials for solenoid valves in the Oil & Gas industry where sour gas environments are common due to the very nature of the processes involved in the extraction of natural gas and crude oil.
This article also provides information on the problems sour gas causes to equipment including hydrogen embrittlement and sulphide stress cracking.
We discuss NACE (National Association of Corrosion Engineers) and the standards that have been specifically written for the Oil & Gas industry.
Finally, a case study is included showing how ASCO Numatics have developed NACE compliant solenoid valves for flow control in harsh industrial and offshore environments.
But first things first, what is a solenoid valve?
asco Solenoid Valves
ASCO solenoid valves are used for the fluid control of air, water, oil or gas normally consisting of an operator and valve body – the operator includes the coil, core, core tube, shading coil and spring. The solenoid valve body is made up of orifices where a disc, piston or diaphragm is positioned. When an electrical current passes through the solenoid valvea magnetic field is created which pulls the core into the open or closed position.
What Is Sour Gas?
Simply, it is natural gas which contains hydrogen sulphide, H2S (the rotten egg smell).
To be precise, if the H2S concentration is >4PPM (parts per million) then natural gas is considered to be sour.
I should say at this point that different countries/agencies have different opinions on the thresholds of what defines sour gas. Hydrogen sulphide is extremely toxic and is also extremely corrosive to pipework and fluid handling equipment when in the presence of water. This type of corrosion is often referred to as Hydrogen Embrittlement.
Hydrogen Embrittlement & Sulphide Stress Cracking
I should say at this point, I am not a chemistry or physics teacher, nor do I confess to being an expert on this topic. There have been lots of papers written about hydrogen embrittlement and there is genuine confusion and disagreement between leading scientists regarding cause, diagnosis and prevention.
However, I will try to provide a basic overview. If there are any experts reading this, feel free to contribute your thoughts on this article. Perhaps, you can give our readers a better explanation and we can feature your contributions on a comment box below.
Hydrogen embrittlement is caused when hydrogen reacts with metals reducing their tensile strength resulting in a weaker structure. It does not affect all metals equally, with the most susceptible being high strength steels, aluminium and titanium alloys. To try and explain the process, hydrogen ions force their way into the grain boundaries of the alloy.
This reaction creates molecular hydrogen which effectively takes up more space between the grain boundaries and weakens the bonds between the grain. This reduces ductility, toughness and tensile strength to a point whereby the alloy cracks.
A major issue with this type of metal failure is that hydrogen embrittlement is difficult to identify. Cracks can be extremely small and only seen under a microscope.
However the end result is likely to be a sudden catastrophic failure. In the onshore and offshore oil and gas industry such failures can lead to major disasters.
Video: Animation of Explosion at Tesoro’s Anacortes Refinery
An explosion and fire led to the fatal injury of seven employees when a nearly forty-year-old heat exchanger catastrophically failed on April 2, 2010 as a result of high temperature hydrogen attack.
This form of corrosion is slightly different to hydrogen embrittlement but the principals remain the same and the unfortunate accident emphasises why it is so important to minimise the risks of such catastrophic metal failures.
There are many manufacturing processes which can cause hydrogen embrittlement such as cathodic protection, electroplating, phosphating and pickling. In the oil and gas industry, particular concern is reactions between alloys, acids and chemicals which brings us nicely onto the topic of sulphide stress cracking.
Sulphide Stress Cracking
Sulphide stress cracking is a form of hydrogen embrittlement. Natural gas and crude oil often contain large amounts of hydrogen sulphide. A reaction between the alloys and hydrogen sulphide create metal sulphides and atomic hydrogen. Atomic hydrogen then either combines to make H2 at the surface of the metal or it diffuses into the metal.
This inevitably results in reduced ductility of the alloy and causes stress cracking.
In the oil and gas industry where sour gas environments are common place, the selection of materials for such environments is critical.
NACE MR0175/ISO 15156
NACE MR0175/ISO 15156 is an internationally recognised standard that details requirements and recommendations for selection of alloys.
I’m sure most people reading this will know who NACE are and what they do but for those who don’t:-
NACE was established in 1943 and its mission is to “protect people, assets and the environment from corrosion.” It has over 35,000 members and is recognised globally as the “premier authority for corrosion control solutions.”
NACE MR 0175 / ISO 15156 describes general principles and gives requirements and recommendations for the selection and qualification of metallic materials for service in equipment used in oil and gas production and in natural gas sweetening plants in H2S -containing environments, where the failure of such equipment could pose a risk to the health and safety of the public and personnel or to the environment.
It can be applied to help to avoid costly corrosion damage to the equipment itself – supplementing, but not replacing, the material requirements given in the appropriate design codes, standards or regulations.
(Extract taken from ISO Materials For Use In H2S-Containing Environments In Oil & Gas Production http://www.iso.org/iso/catalogue_detail.htm?csnumber=66640)
Solenoid Valves – A Case Study By ASCO
ASCO Solenoid Valves Series 327
Solenoid valves are widely used throughout the oil and gas industry.
Applications can include actuator piloting, compressor unloading, redundant control systems and utilities control. Conditions in upstream offshore environments can be extremely harsh as well as being certified as explosive atmospheres.
As already discussed, sour gas is a major problem in such environments meaning there is a requirement for hazardous area solenoid valves that are not only explosion proof but also highly resistant to corrosion.
ASCO Numatics are part of the Emerson group and are a global leader in the design and development of solenoid valves. ASCO were asked to develop a direct acting solenoid valve specifically for sour gas environments.
The design brief was fairly simple:-
- High corrosion resistant explosion proof solenoid valve suitable for upstream offshore conditions
- NACE compliance to prove suitability for sour gas (H2S) environment including solenoid enclosure internals
- High efficiency; reliable operation at lower power levels
The brief may have been simple but ASCO spent a large amount of time, money and resource developing a solenoid valve to meet the above requirements.
ASCO WSCR327 Solenoid Valves
Firstly, the new solenoid valve is constructed of corrosion-resistant materials to meet NACE MRO175/ISO15156 standards.
All parts that may come into contact with sour gas are NACE compliant but furthermore, so too are the internal components which may be exposed to sour gas during installation and routine maintenance.
The solenoid valve can be supplied as a 3/2 direct operated solenoid in either ¼” or ½”.
Flow rates up to 1.8m3/h are possible and a non breathing design means contaminated air from the environment will not pass through the valve eliminating the potential for corrosion.
The valve is a member of the ASCO 327 solenoid valves range and is based on the principle of a balanced poppet type construction. It can be mounted in any orientation and is available with low powered solenoid operators (1.8w). The low power consumption helps to reduce the running costs and increase service life.
ASCO solenoid valves can also be supplied in explosion proof and intrinsically safe options and are also EXIDA & TUV certified (IEC 61508 Functional Safety) so can be used in safety applications up to SIL-3.
ASCO 327 Valves (Offshore/NACE) Design
ASCO WSCR solenoid valves have been tested for 50ppm sour gas concentration both externally and inside the solenoid housing.
ASCO Solenoid Valves – 327 Range Benefits
- Corrosion resistant and NACE compliant valve for the ambient including the solenoid internals
- Direct acting; functioning on very low electrical power without the need for piloting
- Same solenoids for different ATEX/IECEx protection methods covering most common zones: Ex d – Ex emb – Ex ia
- Compact, low weight with good connectivity
- Latest ATEX/IECEx explosion safety classifications for highest safety
- Low power consumption – minimum of 1.8 watt for Ex d & e mb and 0.5 watt for “ia
- Suitable for safety systems; Exida certified; SIL 3 capable
T&D are an Authorised Distributor for ASCO Numatics and work in close partnership with their engineering team to help develop solenoid valves that meet our clients flow control requirements.
Our combined extensive knowledge of the oil and gas industry enables us to design value engineered solutions that meet strict industry guidelines.
ASCO solenoid valves are a quality and reliable solution that provide real benefits to installation engineers and end users throughout the whole lifecycle of the product – they are the most specified valves for critical and safety related applications.
- ATEX Solenoid Valves – ASCO Valves for International Hazardous Area Installations
- ASCO Valves – Selecting & Ordering The Correct Valve
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