For manholes made of stainless steel, can standard manholes with butt-welded flanges be used?
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For manholes made of stainless steel, can standard manholes with butt-welded flanges be used? It might be difficult to explain clearly; as an example, take HG/T21521-2014 – vertical lidded flanges with radial butt-welded manholes. The material details are shown in the figure below: It can be seen from this table that there is no category for stainless steel materials, and the same is true for the maximum allowable pressure values. However, the example markings show cases where stainless steel is used. I have been puzzled by this issue for a long time. The leader believes that this material is not listed in the material details, so the standard cannot be applied; instead, it is necessary to follow guidelines on a \"referential\" basis. In my opinion, the material only needs to meet the requirements specified in HG/T 20514, and it can be used directly as shown in the marking examples. For queries regarding cases where there is no maximum allowable operating pressure, this is actually easy to resolve – one simply needs to adopt the maximum allowable operating pressure corresponding to pressure-temperature conditions for flanges as specified in HG/T 20592-2009. But it is also puzzling why, among the various standards for manholes, materials are distinguished from one another Completely baffled
1. Personally, it is feasible to use them as a reference – that is, stainless steel flanges that can withstand the permitted operating pressure, with the rest being based on swivels of corresponding grades； 2. For butt welding, stainless steel is not used; instead, a standard for manholes lined with stainless steel has been established ； 3. The main consideration is still cost-effectiveness – as stated in the relevant explanations in the compilation guidelines for HG/T 21514~21535-2005 ；
I agree with the opinion above; the reason why stainless steel wafer-type butt-weld flange manholes are not included in the standards is mainly due to economic considerations. In cases where stainless steel must be used, it can be designed as a custom solution.
For reference only – it implies that it can’t be used directly in the form of a \"standard component\", right?
Yes, the standard number should include a reference. As specified in HG/T21518-2014 (for reference), when using standard components directly, it is not possible to indicate the material and other details, which can lead to misunderstandings.
Marking examples can be used; simply use the material code according to HG/T20514.
That material code itself is also used as a reference.
The section on standard materials for manholes specifies stainless steel, but it is not listed.
Following the standard component structure directly is feasible
The material code can be determined in accordance with HG/T21514-2014; the design shall refer to HG/T21518-2014 or be designed as a non-standard manhole.