1. I understand that Factor of safety on UTS as per div 1 changed with times as below:
Proior to 1980 = UTS / 5
After 1980 = UTS / 4
After 1999 = UTS / 3.5
Please correct me if I am wrong.
2. Similarly I wish to know what is the change with respect to ASME Sc VIII Div 2?
The Design Margin against UTS has been 3.0 from when Div 2 was originally released until 2007. Then it was reduced to 2.4. In 2017, Div 2 was split into Class 1 with a Design Margin against UTS of 3.0 and Class 2 with a Design Margin against UTS of 2.4.
And the Design Margin on Yield has always been 1.5. You'd need to consult the appropriate Appendices in Section II, Part D for the margins in the creep regime.
Thank you DriveMeNuts.
Yes interested in Div 3 please.
In similar lines of Div 1 and 2, what is the change record of allowable stress criteria in terms of UTS and YS since this code section introduction.
"1. I understand that Factor of safety on UTS as per div 1 changed with times as below:
Proior to 1980 = UTS / 5"
You are off by several decades. If I recall correctly the design margin in Section VIII (there was no Div 1/Div 2 at the time) based on tensile strength changed from 5:1 to 4:1 sometime around 1950.
The first change dates back to the Second World War with the publication of Code Case 979, which permitted a reduction in the design factor on tensile strength from 5 to 4, provided additional requirements were met. This was primarily motivated by the need to conserve material, but also drew on successful experience with some boilers in the 1930s, which were permitted to use a design factor of 4 if they were required to be inspected annually. This change was subsequently incorporated into the Code after WWII, bearing in mind that most vessels were designed to Sections I/VIII back then (Secs. III and VIII-2 were not published until 1963 and 1968, respectively).
Further useful information can be found in 'Companion Guide to the ASME Boiler and Pressure Vessel Code, Chapter 40' and the Section III and VIII-2 criteria documents.
The change from uts/4 to uts/3.5 was made to make asme viii-1 more in line with European codes. Due to uts/4 requirement asme vessels were much thicker than comparable European ones.
European codes are typically UTS/2.4.
It was ASME VIII-2 which also adapted to compete with European codes.
The Inspection and NDT of European codes are similar to VIII-2, however the certification of a European vessel design (i.e. CE marking) is less arduous than Div 2 U2 Stamp. For CE marking, an independent engineer needs to sign off the design, however is not liable if something bad happens. I understand that VIII-2 requires an independent engineer to endorse the design as though it was their own, and hense is liable upon failure.
An ASME VIII-1 vessel with its UTS/3.5 margin is built like a brick outhouse. There is no equivalent in Europe.
Regardless of category, no independent engineer needs to sign off on anything. The nobo usually verifies if the required steps under the applicable module have been taken appropriately. That’s a different story.
Huub
- You never get what you expect, you only get what you inspect.
Sperko's claim that the design margin "stayed at 5 until 1943 when is was changed to 4 largely to conserve materials during WWII" sounds very plausible but it just isn't true. Here's a link to the 1943 edition of ASME Section VIII which shows several materials with an allowable stress set to 1/5th of their tensile strength, not 1/4th:
The 4:1 design margin actually came from the API-ASME code published in 1934. The API-ASME and ASME codes merged in the early 1950s and ASME adopted API-ASME's less conservative allowable stresses.
