Fabricators and repair contractors working within industrial settings are becoming more exposed to P91 steel with each passing year. Where only a few decades ago—in the 1960s and 1970s—P22 steel was standard for most industrial valves, P91 has since bucked the trend and become the go-to material for design, installation and fabrication.
It’s not hard to see why P91 is rapidly antiquating P22. Aptly named for its 9Cr-1Mo-V composition, P91 comes with higher operating temperature capabilities, extreme durability, lightweight installations and quicker repairs. It’s simply an all-around improvement over P22.
All of these benefits are optimal for industrial settings, but they can present a few challenges to an inexperienced industrial valve repair service in Utah. Welders and repair technicians have to thoroughly understand the properties of P91 in their own right, as well as how they stack up against P22, to deliver repairs that are thorough and lasting.
Heat’s role in properly repairing P91
Fabrication of P91 can be incredibly challenging. Instead of approaching something like valve repair from a basic SMAW or GTAW welding standpoint, preparation and finishing must first be considered. Specifically, welders must remember the importance of preheat and post-weld heat treatments to ensure repairs are thorough and the integrity of the alloy is maintained.
P91 valves and pipes are typically preheated to the 400- to 500-degree range, to reduce overall hydrogen levels. This is the control temperature for any welding repairs being made. Fabricators are advised to stay below 600 degrees, however—above this point, the weld puddle can become messier and more difficult to work with, thus raising the potential for sloppy or ineffective welds.
To relieve stress in heavier P91 pipe and valve applications (those several inches thick), a high hold temperature is required—often 1,400 degrees for one hour per inch of thickness, with a minimum of two hours of total soak time. Induction heating adequately softens the metal so it better accepts welds.
Finally, in order to ensure welds hold and the stability of P91 steel isn’t interrupted, controlled cooling is critical. Rapid cooling will stress the metal and can cause microfracturing. The typically recognized safe rate of P91 controlled cooling is 400 degrees per hour.
Welding to the D10 standard
Every industrial valve repair service in Utah that provides welding repair for P91 piping and valves needs to be familiar with the D10 standards and guidelines for piping and tubing welds. Not only do these guidelines establish proper preheating and cooling guidelines for chromium-molybdenum steels, they also cover proper current settings, weld appearances and more, across GTAW and SMAW welding modalities.
Get familiar with P91
Many welding companies and valve repair technicians have been in the trade since P22 was a standard. Transitioning to more P91-based work has been unavoidable and will continue to be the standard in any welder’s repertoire of work for the future.
For welders, identifying P91 projects and approaching them correctly is imperative. For industrial plant managers and operators, choosing an industrial valve repair service in Utah that’s intimately familiar with P91 welding projects is equally as important. To learn more about our capabilities, contact Intermountain Valve Services Inc. today.
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