|
For base metal with carbon content ≥ 0.18 %: The combined percentage of Cu + Ni must be ≤ 0.15 %.
For base metal with carbon content < 0.18 % or unknown carbon content : the combined percentage of Cu + Ni + Cr must be ≤ 0.15 %.
For weld metal : the combined percentage of Cu + Ni + Cr must also be ≤ 0.15 %.
These limits are in place to prevent the formation of iron fluorides , which can build up in the system and cause material degradation . These requirements ensure that even after prolonged exposure to HF , the material integrity is more likely to remain uncompromised , reducing the risk of leaks and failures .
Fastener Requirements
Fasteners play a crucial role in ensuring the mechanical integrity of the valve assembly . Just like the valve bodies and internal components , fasteners used in HF Alkylation service need to meet stringent corrosion resistance requirements to withstand the aggressive HF environment .
External Bolting :
For bolting on pressure-retaining components like valve bodies , the standard material is ASTM A193 Grade B7M studs , paired with ASTM A194 Grade 7M or 2HM nuts . The “ M ” designation indicates these materials are specially processed to reduce hardness and improve toughness , preventing embrittlement from HF exposure . ASTM A320 L7M studs may also be used upon the end user ’ s request , providing similar corrosion resistance .
|
standards . These methods are more effective than X-ray fluorescence for detecting elements like carbon copper , aluminum , etc . at the required precision .
Special Coating for HF Detection
HF valves require a specific HF Acid Detecting Paint , typically yellow , that changes color to red when exposed to HF . This coating provides a critical early warning system for potential leaks , helping operators respond quickly to prevent incidents .
Common Challenges with HF Valves
Leakage and Failures :
Leaks around the bonnet and stem seals are common failure points in HF valves . However , with the right material selection , maintenance program , and regular inspections , these issues can be minimized .
Valves in Hydrogen Service
When it comes to handling hydrogen , valves are critical to keeping everything running smoothly and safely . But as many in the industry know , hydrogen service is no walk in the park . Because of its unique properties — like hydrogen ’ s ability to seep into materials and cause embrittlement — it requires special consideration from start to finish . The following are some key factors to consider when choosing and maintaining valves in hydrogen service .
One of the first steps when working with hydrogen service is understanding the environment in which the valves will operate . Hydrogen is a tricky substance — its molecules are tiny , which means they can sneak into valve materials and cause damage over time , leading to what is known as hydrogen embrittlement . This is particularly a problem in high-pressure applications , where hydrogen can really put materials to the test .
To handle hydrogen safely , it is crucial to evaluate the temperature , pressure , and any contaminants that might be present . This will help operators choose the right valve materials and design features . Documents like ASME B31.12 are great resources for understanding the necessary design and material requirements for hydrogen service .
|
Testing
Leaks in hydrogen systems can be dangerous , and because hydrogen is so small , it is tough to detect . That is why most hydrogen valves undergo helium leak testing . Helium mass spectrometry is often used for this purpose .
Common Challenges : Hydrogen Embrittlement and Leakage
To give a more detailed explanation of Hydrogen embrittlement it is a phenomenon where hydrogen atoms infiltrate a metal , making it brittle and prone to cracking under stress . This is especially problematic in high-pressure hydrogen service , where hydrogen molecules can penetrate valve materials over time . Essentially , hydrogen atoms slip into the metal ’ s structure , reducing ductility and load-bearing capacity , causing fractures that would not normally occur .
In hydrogen service , even materials that are typically strong in other environments — like high-strength steels — can become vulnerable to embrittlement . That is why it is so important to choose materials that can resist this weakening effect .
Hydrogen embrittlement is a slow process , but over time , it can cause catastrophic failure if not properly addressed . Regular inspections and careful material selection are key to avoiding embrittlement-related problems . Following standards like NACE MR0175 / ISO 15156 , and inspecting the valves regularly , can help prevent these issues .
Leakage is another big concern . Because
|
hydrogen molecules are so small , ensuring proper sealing is essential . Using valves with specifically designed for Hydrogen Service and regularly testing them for leaks ( using helium ), can significantly reduce the risk of leaks .
Dealing with hydrogen service means paying attention to the details — whether it is choosing the right materials , verifying fasteners , or testing for leaks . By following the proper standards and staying on top of maintenance , operators can ensure the hydrogen valves stay safe and reliable .
It is recommended for operators to follow guidelines like ASME B31.12 and NACE MR0175 / ISO 15156 and make sure to test everything before it goes into service . When it comes to hydrogen , it is always better to be safe than sorry !
Valves in Chlorine Service
Chlorine is a highly reactive substance that requires careful handling , especially when it comes to valve systems . Industry standards like the Chlorine Institutes Pamphlet 6 outlines the recommended practices for piping systems , including valves used in dry chlorine service , and provides critical guidelines for cleaning , testing , and shipping to ensure safety and longevity .
Choosing the right materials for valves in chlorine service is essential for preventing corrosion and ensuring long-term durability . Dry chlorine is less corrosive than wet chlorine , but even small amounts of moisture can lead to the formation of hydrochloric acid ( HCl ) and hypochlorous acid ( HOCl ), which are highly corrosive to
|
|
Every fastener must be carefully marked and verified for compliance . It is essential to check 100 % of the external bolting for proper identification stamps , ensuring the materials meet industry standards .
Additional Pressure Testing :
|
Choosing the right material is essential to preventing failures . Not every metal can stand up to hydrogen ’ s unique challenges . For example , high-strength steels , which are often great for other environments , can become brittle and crack in hydrogen service . |
||
|
HF valves often undergo extra pressure testing to confirm their durability under operating conditions . This testing helps ensure that the valve will remain leakfree despite the high pressure of an HF environment . Preferred testing methods include the use of a Mass Spectrometer to help find leaks .
Positive Material Identification ( PMI ):
|
Instead , austenitic stainless steels materials ( 316 and 304 ) or nickel-based alloys ( Monel and Hastelloy ) are commonly used because they resist embrittlement . But even here , personnel need to be cautious . Monel , for instance , is typically used in liquid hydrogen service rather than gaseous hydrogen . Industry guidelines like NACE MR0175 / ISO 15156 can help make the best material choices . |
||
PMI is a critical step to ensure that the materials used , particularly Low RE Carbon Steel , meets the specified requirements for HF service . Techniques like Optical Emission Spectroscopy ( OES ) or Laser-Induced Breakdown Spectroscopy ( LIBS ) are preferred for this , as they can detect the low levels of residual elements necessary for compliance with HF valve |
Fasteners Matter Here Too
Do not forget about the bolts ! The fasteners holding the valves together also need to resist hydrogen embrittlement . Materials like ASTM A193 Grade B8M or Alloy 718 are often the go-to choices because of their toughness and resistance to hydrogen .
|