The MSS SP-160 standard, published by the Manufacturers Standardization Society of the Valve and Fittings Industry, specifies design, testing, and quality requirements for a variety of valves, including Hydrogen Fluoride (HF) Alkylation Service. The standard aims to improve the safety and reliability of valves throughout the industry.
By Paul Heald – Vice President of Product Engineering, Specialties & China Operations – Bonney Forge
In September 2024, a new standard, MSS SP-160, was published by the Manufacturers Standardization Society (MSS). It was developed by a Task Group committee within MSS Technical Committee 410, which focuses on severe and special service valves.
The committee was comprised of end users, valve manufacturers, distributors, and valve modification services. However, it was the end user’s participation that had a significant impact on reducing the amount of publishing time for this standard.
Why was MSS SP-160 Published?
The MSS SP-160 standard was created due to a number of challenges. Small valve leaks not detected by industry standard test methods indicated a need for more stringent methods.
Additionally, previous approvals of specific industry standard specifications for manufacturers were no longer available and various specifications utilized by end users needed to be harmonized.
Since typical pressure decay test methods were deemed incapable of detecting small leaks and/or defects, comparative non-destructive examinations (NDE) on known defective valves were performed.
Even though NDE radiographic testing (RT) can potentially detect defects, it is not 100% effective. However, a Helium Mass Spectrometry Test – Accumulation Technique was found to be the most result oriented.
An Overview of The MSS SP-160 Standard
*The MSS SP-160 document provides several sections outlining specific and current stipulations.
*Author’s Note: These are generalized excerpts from the overall MSS SP-160 document. There are too many additional requirements to provide details adequately without the actual MSS SP-160 report.
These include:
- Scope
- Valve Design
- Materials
- Definitions
- Foundry Requirements
- Welding
- Weld Repairs
- PWHT and NDE Testing.
- Marking and Tagging
- Preparation for Shipping and Documentation
The MSS SP-160 document also includes an annex, appendix, tables, and figures for documentation and trim configurations. Revisions in the document remove the minimum regulations for upgraded valves manufactured prior to the first publication.
Listed below are more detailed outlines of these sections in The MSS SP-160 Standard:
Scope, Valve Design, Materials, and Definitions
Scope applies to gate, globe, check, butterfly, and plug valves. It does not apply to valves used in hydrogen fluoride acid production.
Valve design includes many key standards, such as low emissions performance and compliance with industry design standards. For gate, globe, and check valves, the seat pocket is Alloy 400, and seats are installed into low RE carbon steel using a nickel butter pass layer. The seats are press-fitted and seal-welded to ensure a secure and leak-tight connection.
There are options for grease injectors, nickel-lined packing stuffing boxes, check seal welded hinge pin plugs, and PTFE soft seats. Plug valve (cap/ stem) designs, for instance, are to be implemented to prevent water accumulation. Gear operator options are outlined in this section as well.
Materials to the American Society for Testing and Materials (ASTM) standards for cast and forged bodies, bonnets, and covers are low RE carbon steel, Alloy 400 and C276. Cast and forged materials of components are to ASTM standards (with some specific components to different materials). Bolting, lubricants and anti-seize directives are also included in the document.
Foundry Requirements, Welding, Welding Repairs, and PWHT
Foundry requirements must be documented to foundry qualifications and 1st articles. Therefore, casting simulations are needed to determine discontinuities and pattern/rigging according to the simulation results.
Shrinkage or microporosity are not allowed through ¼” wall thickness based on simulation or final NDE on machined surfaces. Any foundry changes must go through a new casting simulation, and partial furnace changes are not permitted.
All welds shall be made to weld procedures, set and qualified by welders to the American Society of Mechanical Engineers (ASME), ISO, and the National Association of Corrosion Engineers (NACE). Heat affected zone hardness surveys for weld procedure qualifications need to be in accordance with NACE. Weld repairs must be applicable to ASME and ASTM standards. Through-wall repairs on any castings are not permitted without prior written approval from the end user.
Post Weld Heat Treatment (PWHT) stipulations will be based on specific material as well as applied to weld repairs and nickel butter passes using the specified heat treatment temperatures. Post Weld Heat Treatment is not necessary for C276. Qualified welding procedures to NACE for a nickel butter pass may not be applicable to PWHT.
Radiographic Testing (RT) of carbon steel body and bonnets (cover) shall be modified to critical areas. For Alloy 400 and C276 components, 100% volume RT is required and must be approved to Level III standards. Positive Material Identification (PMI) using XRF or OES needs to be conducted according to the applicable API standards.
Testing first with helium is recommended. During the comparative testing, it was found that testing water first blocks or plugs a small through-wall leak from being detected. In the event of water being used for initial testing, the valve needs to be dried to the temperature and minimum length of time requirements.
Helium Mass Spectrometry – Accumulation Method is Preferred
The accumulation method is the recommended approach for helium mass spectrometry leak testing. Other methods may be used but they must involve a bubble test and a helium detector probe. Comparative testing revealed these two methods are less effective when used individually. When combined, they can reliably detect small leaks.
Marking and Tagging
Marking and tagging a tag is necessary with specific details. Preparation for shipping must entail an acid-indicating painting to the figures of the areas of that must be coated on valves.
Following the publication of the MSS SP-160 Standards, an erratum was published that added a sub paragraph specifically for plug valves to be “Certified Low-Leaking Valves.” A manufacturer shall provide a written guarantee that the valve will not leak above 100ppm for five years.
The MSS SP-160 is recommended for inclusion in future editions of industry design standards publications.
About the Expert
Paul’s career began more than 40 years ago as a Valve Design Engineer. He has participated in various industry standards committees and is an active voting member of API, ASME, MSS, and the MSS Board of Directors. He joined Bonney Forge in 2009 as Vice President of Product Engineering and is responsible for Specialties and China Operations, working closely with both domestic and international operations and sales.