What is the difference between the Chinese version of ASME B31.1-2007 for power piping and ASME B31.3 for process piping? What are the two...

Power pipelines are mainly used in power plant systems...

What are the differences between B31.1 and B31.3 pipes? _ Baidu Wenku http://wenku.baidu.com/link?url=UR-Nx_Ai6BMNsp-2JOdlXqnAo-eHYKhP_NWDM_nig7LDkSjWoZxHAL0ZaQ4uciDzxcZrTRaIsSN8bIHy-kHaKtA6B2izdpd6PkisGx9J30a The first difference is that the formulas for calculating the wall thickness of pipes under these two standards are not identical. The second difference is that the allowable stress specified in ASME B31.1 is stricter than that in ASME B31.3. The allowable stress for pipeline materials under ASME B31.1 is approximately 1/3.5 of the tensile strength of steel; in earlier versions, the allowable stress for pipelines was set at 1/4 of the steel’s tensile strength. The latest version from 2007 introduced the biggest change to this value since the inception of B31.1, changing it from 1/4 to 1/3.5. In contrast, the allowable stress for pipeline materials under B31.3 is approximately 1/3 of the steel’s tensile strength. For example, the allowable stress for A106B at room temperature is approximately 117 MPa according to B31.1, while it is around 135 MPa according to B31.3. Although the allowable stresses in version 2007 of B31.1 have been relaxed, as a precaution, version 2007 of ASME B31.1 has raised the requirements for welding. The third one is different; the stress calculation formulas are different. AMSE B31.1 provides relatively clear stress calculation formulas, whereas ASME B31.3 only includes some conceptual aspects related to stress calculations. The stress calculations for B31.3 in CAESARii reflect the spirit of stress calculation as outlined in this standard; however, there is no standard answer regarding the formulas used for such calculations. Furthermore, in the stress calculation formula of B31.1, the effect of torsion is not taken into account, whereas in B31.3, the effect of torsion must be considered (hehe, it seems this is the only aspect in B31.3 that is more stringent than in B31.1). The fourth difference relates to pipe deflection. ASME B31.1 specifies a clear limit for deflection, which is 2.5 MM. ASME B31.3 does not provide such a specification; in practice, 3 MM is generally adopted. Correspondingly, B31.1 has clear rules regarding the spacing between pipe supports and hangers, while B31.3 lacks any regulations on this aspect. The fifth difference is that the scope of application of the two standards is different. Due to the strict requirements, B31.1 involves the use of large amounts of steel; for economic reasons, it is generally only applicable to the external pipes of power station boilers. B31.3 has a much wider range of applications, including in the oil, chemical, and pharmaceutical industries. Furthermore, ASME B31.3 states that \"this standard does not apply to pipes outside the boiler; for standards related to pipes outside the boiler, please refer to ASME B31.1.\" The sixth difference relates to fittings. Flange connections are commonly used in B31.3 pipes. In pipes of type B31.1, flanges are used less frequently (but not at all never), and instead welding is employed directly. This is mainly because power pipelines are generally at high temperatures (550 degrees is common, and 600 degrees is also frequent) and high pressures (the pressure in some pipelines can reach 47 MPa); as a result, flanges find it difficult to resist the effects of temperature and pressure without allowing fluid leakage. b31.3 Pipelines involve issues such as jacketed pipes, expansion joints, and direct burial of pipelines ； Section b31.1 explicitly prohibits the use of expansion joints on the external pipes of boilers, and direct burial is also not allowed. As for the jacket, it is not needed at all because there is no such process flow in the power plant. The seventh difference is the issue of dynamic load shock. When performing stress analysis on B31.3 pipelines, impact loads such as water hammer and steam hammer are rarely considered. For the external pipes of subcritical power plant boilers within the B31.1 range (especially units below 300MW), water hammer and steam hammer impact loads can also be disregarded. However, impact loads such as water hammer and steam hammer in the supercritical and ultra-supercritical units of power plants have a significant effect on the stability of pipelines (especially steam hammer), and these factors need to be carefully considered. The eighth difference is the stress increase factor during stress analysis (also known as the stress concentration factor, stress enhancement factor, or stress increase coefficient – well, there’s no consistency in the translations used in China). In B31.3, the stress amplification factor is divided into an in-plane stress amplification factor and an out-of-plane stress amplification factor. Generally speaking, the stress amplification factor out of the plane is smaller than that within the plane; this makes it easier to conduct stress analysis on pipes. In B31.1, instead of distinguishing between the in-plane stress amplification factor and the out-of-plane stress amplification factor, the concept of stress amplification factor is used. The stress amplification factor in B31.1 is essentially the same as the in-plane stress amplification factor in B31.3. In other words, the stress increase factor for B31.1 is more conservative.

I have a question: why does the flange used here jump directly from class 25 to 150 lbs, without any intermediate grade? Are there Classes 75 or Classes 100? There’s no entry for this in ASME B16

I don’t know that. It was half a year ago – how could one still remember it? :L

Conversion between American Standard Class pressure ratings and MPa values: 1 pound per square inch = 6894.8 Pa. Therefore, Class 150 corresponds to 6894.8 x 150 = 1.034 MPa. The standard value is 2.0 MPa; what’s the reason for this? It turns out that the reason for the difference in the domestic application of standards related to the American standard in HG20592-20635 lies in this: the allowable stress for materials according to the American standard is determined based on the average allowable stress of materials at 450 degrees Celsius, while in domestic applications, 120 degrees Celsius is used as the basis for calculations; as a result, the allowable stress for materials differs. Therefore, the conversion is as follows: 1.034 × allowable stress at 120 degrees / allowable stress at 450 degrees is greater than 2, so it is rounded to 2.0 MPa. That is, Class150 2.0MPa; the values for the others are also obtained through similar calculations and rounding!