Valve material issue

In the ASTM and ASME standards of the United States, the 91 steel series, classified by their intended use, includes: A213 T91 – ferritic and austenitic seamless steel tubes for boiler superheaters and heat exchangers; A182 F91 – forged alloy steel tubes, flanges, forged fittings, valves, and other components for high-temperature applications; A234 WP91 – forged fittings made of carbon steel and alloy steel for moderate to high-temperature use; A200 P91 – ferritic alloy steel seamless tubes for use in the petrochemical industry; A336 F91 – steel forgings and alloy steel components for high-temperature and high-pressure environments; A199 T91 – cold-drawn alloy seamless tubes for use in heat exchangers and condensers; A369 FP91 – forged hollow tubes made of carbon steel and ferritic alloy steel for high-temperature use; A335 P91 – ferritic seamless tubes for high-temperature pipelines. All these steel grades have similar compositions; the differences in their properties arise mainly from their respective applications. For example, T91 has a heat resistance strength of ≥ 585 Mpa, while WP91 has a σb value of 590–760 Mpa. Additionally, forged products are required to have a reduction in cross-sectional area of >40%, whereas this requirement does not apply to fittings. These differences are minor and easy to meet. In fact, all 91 series steels are modified versions of the original 9Cr-1Mo steel grades, with strengthening elements such as V, Nb, and N added to them. It is commonly referred to as martensitic heat-resistant steel, but according to American standards, those with a Cr content of less than 10% are classified in the ferritic series; therefore, the name used in the standards remains ferritic-type (in fact, the microstructural type can vary depending on the heat treatment processes applied, so there is no need to stick strictly to the name). In China’s GB5310-95 standard, the equivalent steel grade is 10Cr9Mo1VNb (seamless steel tubes for high-pressure boilers); compared with another Chinese grade, 1Cr9Mo1VNb, it contains less nitrogen. The heat-resistant steel that is truly equivalent to American 91 steel is 1Cr9Mo1VNb(N). Steel 91 was developed through research at the Oak Ridge National Laboratory in the United States starting in the 1970s; it was included in the ASME standards in 1983 as SA213-T91. Its purpose was primarily to fill the gap in steel materials suitable for use in new steam and water pipelines in the temperature range of 600–650°C, between pearlitic heat-resistant steels and austenitic stainless steels. The Type 91 steel has excellent properties at room temperature, as well as good endurance and creep resistance below 650°C. It features a low linear expansion coefficient, good workability, and a relatively low cost (with an alloy content of 9.5–11.5%). Its superior structural stability over long periods of use has enabled it to gain rapid widespread adoption and development. In our country, pipeline testing of P91 began in the early 1990s and it was included in standards in 1995. By the end of the 1990s, it was gradually adopted for use in valve fittings, tees and other pipe fitting forgings, as well as in industrial components that require high heat resistance and are used in environments below 620°C.

The spectra of different brands may yield varying results when measured. The compositions of F91 and P91 are not very different; therefore, the sensitivity of the spectrometers varies, which may lead to differences in the results obtained. If you’re not confident, you can take a sample for manual testing.

Sometimes it’s not necessary to approach problems from a technical perspective; by focusing strictly on the wording of the contractual agreements, it might be possible to resolve issues more effectively than by worrying about the materials used. Such as terms regarding the guaranteed period of use and the service life. :)

I can learn new poses every day:lol:lol

This post was last edited by elousky on 2019-5-29 at 14:40. P91: the letter P stands for PIPE, while F91: the letter F stands for FORGED. In many cases, P91 is used to indicate the material of valves because the pipes are made of P91; therefore, it is assumed that the valves should also be made of P91. The material used for valves is F91, which falls under A182 – this is the standard practice in the industry. Just like the 20G standard in China, in reality the valves are all 20#. You measured it as P91; it’s likely a problem with your spectroscopy device’s identification. It’s similar to when checking 316 and 316L – some devices show that the elements correspond to 316L, but still label it as 316L.

Thank you. May I ask which element concentrations should be primarily checked to determine whether it is qualified?