Questions regarding the selection of material for pipe fittings in gas stations
Thread Content
I have a question for the experts in this field and am seeking guidance. Currently, seamless steel pipes are commonly used for pipelines in gas stations, with seamless fittings also being used in conjunction with them. The choice of pipe material generally depends on the requirements; L245N PSL2 is typically used. However, some manufacturers opt to use L245M instead when supplying these pipes. According to the specifications in 9711, the acceptable delivery condition for seamless steel pipes does not include M, but the manufacturers insist that this delivery condition has no impact on performance or welding processes. So the question is, are there really seamless pipes and fittings of L245M? It should be incorrect to use steel pipes that meet the 9711 standard as the base material for such fittings. Or, in other words, fittings labeled as L245M are actually not seamless; in that case, is there a significant difference in their pressure-bearing capacity compared to seamless ones? Could this lead to a situation where the required design pressure capacity cannot be met?
This post was last edited by lijie2007521 on 2022-6-4 at 14:48. Currently, in China, the steel used for domestic Sino-Russian pipelines and newly built gas pipelines is mostly material specified in standard GB9711 for pipelines used in petrochemical fluid transport; N and M represent the delivery conditions of the steel pipes. Different delivery conditions also result in varying usage conditions for the materials. The coefficient for seamless steel pipes is generally taken as 1, while that for welded pipes is lower than 1. In the calculation of steel pipe strength, seamless pipes are thinner and offer higher safety levels compared to welded ones. Pipelines are generally designed using equal-strength calculations; for steels of the same grade, the calculated wall thicknesses are similar (such as in the case of straight pipes and elbows). The operability and safety of welding were also considered. Conventional design gives priority to seamless integration. Generally, most large-diameter steel pipes are welded, which is related to factors such as the manufacturing process of steel pipes. Small-diameter ones are basically seamless.
Thank you very much; I’ve truly learned a lot. However, what I really want to know is whether the M delivery condition can be used for station piping or seamless pipe fittings along the pipeline. According to 9711, under PSL2, the M delivery condition applies only to welded pipes; only N, R, and Q are designated for use with seamless pipes. Yet, in earlier designs of station piping, PSL1 was utilized without any specified delivery condition. Can this be interpreted as meaning that there are indeed seamless pipes and fittings corresponding to the L245M condition available for use? To be honest, I still don’t quite understand 9711. I’m looking for a suitable explanation for the situation where pipe manufacturers produce L245M seamless pipes and fittings as alternatives to those made from L245N – for example, the impact on medium and low-pressure piping systems with pressures not exceeding 16 kilograms, or other aspects related to this
This post was last edited by lijie2007521 on 2022-6-4 21:23. To be precise, API 5L, a type of steel used for pipelines, was initially introduced in China as well; later, GB9711 gradually replaced API 5L as the standard. The design standards back then, as well as the processing capabilities for domestic steel, were limited. However, with the construction of large-scale pipelines in the country and the improvement of technical capabilities, many standards and material choices have been upgraded and changed. Including at the present time, many of our new materials and technologies are also in the process of being learned and explored. A significant step was taken toward local production of the products that began to be developed in the first two years (regulating valves, forced-seal ball valves, check valves, gas turbines, compressors, etc.).
CNPC has a uniform regulation: if the steel pipes are to comply with the 9711 standard, seamless steel pipes of grade L360 and below use the letter N, while those of higher grades use the letter Q； All welded steel pipes are M. If the 12459 standard is applied to the fittings, it specifies the condition of delivery; if there are two or more such conditions, they must be selected in the contract. The heat treatment requirements for hot-drawn bent pipes are specified in GB-T 29168.1-2021; SY-T 5257-2012 provides less detailed information.
Thank you, I’ve learned something. Do you think my understanding is correct? For 1.5D elbows, GB12459 is generally used, as 1.5D falls under the category of standard fittings. For small-diameter fittings, seamless pipes are usually used as the base material for manufacturing. According to the fitting specifications, the heat treatment conditions for delivery include grades such as M, N, and Q. Meanwhile, SY5257 applies only to pipeline steel elbows with a radius of not less than 5D, and it is not suitable for the production of 1.5D elbows