The issue of corrosion margin in pressure vessel design
Thread Content
During the design process of pressure vessels, it is generally required by regulations to specify the \"design life\" of the equipment. This serves to protect the design agency by preventing the equipment from being used beyond its intended lifespan, and it also acts as a reminder to the users of the equipment to carry out more frequent inspections and shorten the inspection intervals, thereby avoiding safety accidents. In fact, many design firms also indicate the \"design life\" in their design drawings, but they do not specify the basis for this value in the design documents; as a result, it is impossible to determine the value of the corrosion allowance. This poses a problem for many designers and also results in incomplete design documents. I asked some veteran comrades, and their answers were rather vague and lacked any basis. The key issue, in my opinion, is that there is no basis for determining the annual corrosion rate of materials caused by certain media (it seems that **there are no standards in this regard; I asked experts from the Standards Committee about this as well, and they laughed and said it depends on the designer’s skill level... leaving it up to the designers to use their discretion). If anything exists, it are just some reference manuals, but none of them can be used as standards! I wonder what everyone thinks, or if an authoritative standard can be found. First, thank you all, gentlemen!
This has been discussed many times; you can check the relevant links.
http://bbs.hcbbs.com/thread-400023-1-1.html
The specification for indicating the design life is a general guideline, not mandatory, mainly because there are no exact figures available for the annual corrosion allowance. At the same time, sometimes users request a very long design life and are unable to provide actual corrosion rates, which puts design firms in a difficult position, though there is nothing they can do about it ； In fact, the indicated service life of the equipment is not the most important factor; what matters more is the inspection of the equipment after it is delivered to the user. As long as the wall thickness meets the specified requirements, the equipment can be used safely. Equipment that is supposed to last 20 years is specified in the drawings as having a lifespan of 15 years – does that mean it can no longer be used after 15 years? If it is put into use, it will return to the path of operational inspection.
The corrosion rate can be found in the manual! No problem.
It’s a well-known issue, but it still hasn’t been effectively resolved. What I’m asking is this: there is no basis for determining the annual corrosion rate of materials caused by certain media (it seems that **there are no standards in this regard; designers are left to use their discretion). If anything does exist, it’s just some reference manuals, but those cannot be used as standards! ”Basically, it’s just the designer who picks a value based on intuition.
:Lol, if even the evaluation committee can’t give you an answer, it means this question isn’t easy to answer clearly. It’s all up to the designer to decide. As mentioned on the 4th floor, the focus is on in-service inspection. Although the corrosion allowance is related to the service life, it is itself an estimate, as the corrosion rate is not accurate.
What is indicated on the drawings is the designed service life (this value takes into account the considerations of the design team; it’s meant to prevent people from being trapped in a fixed timeframe, leaving some room for flexibility). It is a recommended value, and it can only be determined whether the equipment is still usable after measurements and evaluations are carried out in conjunction with the local pressure vessel inspection agency – it’s not the case that the indicated number of years means the equipment will definitely last that long. This post was last edited by zhjun on 2009-3-3 10:50.]
There are three ways to determine the corrosion margin: (1) provided by the customer; (2) by consulting corrosion manuals, such as the \"Corrosion Data Handbook\" published by the Chemical Industry Press and the \"Metal Corrosion Handbook\" compiled by the Chinese Society for Corrosion and Protection; (3) based on experience. It is also possible to conduct coupon testing on equipment to provide a basis for future design work. These were topics discussed by the instructor during pressure vessel training. I hope this helps you.
Open Article 32 on page 19 of the Code of Regulations – the clause that stipulates in black and white the required \"design life\" for containers; how dare you wretches fail to comply! To the second floor: Firstly, it is to protect the design firm (by preventing equipment from being used beyond its intended lifespan); Secondly, it serves as a reminder to the entities that use the equipment (to carry out more frequent inspections and shorten the inspection intervals, thereby avoiding safety accidents). However, to date, no authoritative and unified explanation has been provided for this matter, whether it is from the \"Corrosion Handbook\" or by the veteran experts of the Standards Committee; \"it is impossible to determine the appropriate value for the corrosion margin, which poses a problem for many designers.\" The “Acceptance Criteria” really make things difficult for us!
The margins we design are generally determined by senior engineers, with values set based on their experience. It is generally around 1-3 mm. Hehehe
The book on process equipment design provides a detailed explanation; the corrosion rate can be found in metal corrosion handbooks, with different values for the allowable corrosion allowance depending on the material used.