Regarding the proportion of non-destructive testing for pipelines
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Hello, sea friends! Regarding the requirements for non-destructive testing of pipelines: Standard 50184 requires 100% testing at temperatures below -20°C, while standard 50316 mandates 100% testing at temperatures below -29°C. Standard 20801 does not specify any requirements based on the design temperature. To this end, I specifically consulted the explanatory texts of various standards; the explanatory text for standard 50316 states that it is consistent with standard 50235. I noticed that the latest version of 50316 dates back to 2008, while 50235 was updated in 2011, with an earlier version from 1997. Upon reviewing version 50235 from 1997, it was found that this version also covered construction and inspection procedures, and it specified that a 100% flaw detection rate was required at a design temperature of -29°C. It is confirmed that the requirements and provisions of 50316 are accurate. My question is: are the new versions of 50235 and 50184 derived from the old versions of 50235 through updates? Is the requirement of -20°C for 50184 a mistake, or has the requirement been changed? If it has been changed, then 50316 should also be updated accordingly. Logically, the three standards 50316, 50235, and 50184 are all national standards; they are all applicable to industrial metal pipes and have the same scope of application. There should be consistency in design, construction, and acceptance – it seems rather careless! In my opinion, fluids that are non-toxic and harmless at -20°C are not dangerous at all, and 100% flaw detection seems unnecessary from a safety perspective. Just follow it strictly, right? What do the sailors think about this?
There are many standards for this, and sometimes I get really stressed too
For medium pipelines that comply with the \"Code for Design and Construction Acceptance of Pipelines for Toxic and Flammable Media in Petrochemical Industries\" SH3501‑2002, non-destructive testing can be carried out in accordance with this standard. 1. The non-destructive testing of pipeline welding joints shall be carried out in accordance with JB4730 for the evaluation of weld defect grades, and shall meet the following requirements: a) For radiographic testing, the radiographic quality grade shall not be lower than grade AB, and the qualified grade of the welding joint after radiographic testing shall comply with the provisions in the table below ； Percentage of welded joint radiographic inspection and acceptable grade, pipeline class, transported medium, design pressure p in MPa (gauge pressure), design temperature t in °C, inspection percentage %, acceptable grade: SHA – Media with extremely hazardous toxicity (except benzene) and acrylonitrile, phosgene, carbon disulfide, and hydrogen fluoride with highly hazardous toxicity; any value, any value, 100, II. Toxic and flammable media with p≥10.0; any value, 100, II. SHB – Toxic and flammable media with 4.0≤p<10.0 and T≥400: 100, II. Benzene with extremely hazardous toxicity, media with highly hazardous toxicity (except acrylonitrile, phosgene, carbon disulfide, and hydrogen fluoride), and Class A liquefied hydrocarbons with p<10.0 and -29≤T<400: 20, II; p<4.0 and T≥400: 20, II. Class A and B flammable gases, as well as Class B and C flammable liquids with p<10.0 and -29≤T<400: 10, II; p<4.0 and T≥400: 10, II. SHC – Media with moderate or mild toxicity, as well as Class B and C flammable media with 4.0≤p<10.0 and T≥400: 100, II; p<10.0 and -29≤T<400: 5, III; p<4.0 and T≥400: 5, III. SHD – Toxic and flammable media; any value, T<-29: 100, II. b) For ultrasonic inspection, the acceptance criteria for pipeline welded joints after inspection are as follows ； 1) Weld joints requiring 100% ultrasonic testing are considered qualified at grade I ； 2) Weld joints subjected to local ultrasonic testing met Grade II requirements ； C) Welded joints passed Grade I inspection for magnetic particle testing and penetrant testing. 2. The percentage of radiographic inspections for butt weld joints welded by each welder shall comply with the provisions in the table above. Among the weld joints inspected, the proportion of fixed weld joints shall be no less than 40% of the total number of inspected joints, and shall be at least 1 weld joint. Will this addition meet the requirements? Radiographic or ultrasonic testing of welded joints shall be selected in accordance with the following provisions: (1) For steam and water pipes with a thickness of 20 mm or less, when ultrasonic testing is used, radiographic testing covering at least 20% of the total testing area shall also be carried out. ? (2) For pipes and welded parts with a thickness greater than 20 mm and less than 70 mm, either radiographic inspection or ultrasonic testing may be used. ? (3) For pipes with a thickness of 70 mm or more, 100% radiographic testing is carried out when welding has progressed to about 20 mm, and 100% ultrasonic testing is performed after the welding is completed. ? (4) For boiler heating surface tubes with weld joints of Class I, in addition to undergoing radiographic inspection on at least 25% of them, ultrasonic testing shall also be carried out on another 25%.
When standards conflict, we enforce them strictly
Standard specifications are merely for reference; ultimately, verification should be carried out in accordance with the requirements specified in the design documents.
But it must not be below the requirements of the standard specifications
If the designer has specified a flaw detection ratio, that ratio should be followed; if not, the specifications applicable to the project’s execution shall take precedence. The confusion in domestic standards is not limited to just a few areas
The last edit to this post was made by flute6 on 2018-3-21 at 10:50. The standards in use are quite chaotic; it’s similar to the situation with published books, as there is no **designated standard-setting body to oversee them. For safety’s sake, the strictest of all these standards should be followed