Yield strength reduction factor NS-EN 13445

[blckwtr]

Hi, I am currently designing a pressure vessel for inhouse testing of some equipment, and just wanted to know the influence temperature have on the steel. Currently designing the vessel to 10.000psi and 150°C, I see that strength reduces by a factor of between 28% to 34%, which I think is very high. The vessel consist of a pipe API 5,5in casing, with a 23ppf weight class. The wall thickness is by far enough when analyzing it included threads for the endcaps, but the allowable stress does not allow me to use it for this purpose. 13445 is a concervative standard, since the pressure vessel is supposed to stand in a populated area, this on the other hand is not, it is enclosed in a blast proof area. So I am designing it conservative, with my own considerations.

But anyway, I just wanted to know if the steel is regarded "weaker" on such low temperature, and I find it strange that the reduction factors is so low as specified in 13445...

 

[XL83NL]

How did you derive these recued strength values? Where did you took strength values for API 5? I assume you mean API 5L pipe?

 

[blckwtr]

Table 4.2.1 - Yield strength reduction factors for low temperature steel. Interpolating between 100°C and 200°C gave me the avlues for normalized and quenched steel, since end lid and pipe is two different materials. API pipe is casing for downhole, and it is 5,5in outer diameter. 23ppf gives the wall thickness...

 

[XL83NL]

I guess you meant EN 13445-2 table 4.2-1. Does EN 13445 allow the use of this material? If so, what makes you think that API casing falls under this paragraph?

Im still a bit confused on what it is youre actually doing (and im unfamiliar with some things like ppf - what does that mean?); however, from how I know EN 13445, you use a listed material, and determine the allowable pressure based on that materials stremngth allowables that are published in the respective material specification, like e.g. EN 10216-5 for seamless SS pipe. I believe what youre doing is slightly different, but then again I dont really understand what it is youre doing.
Also note that table 4.2-1 kicks in when para 4.2.2.2 is applicable.

 

[blckwtr]

I guess you meant EN 13445-2 table 4.2-1. Does EN 13445 allow the use of this material? If so, what makes you think that API casing falls under this paragraph?

Im still a bit confused on what it is youre actually doing (and im unfamiliar with some things like ppf - what does that mean?); however, from how I know EN 13445, you use a listed material, and determine the allowable pressure based on that materials stremngth allowables that are published in the respective material specification, like e.g. EN 10216-5 for seamless SS pipe. I believe what youre doing is slightly different, but then again I dont really understand what it is youre doing.
Also note that table 4.2-1 kicks in when para 4.2.2.2 is applicable.

- EN 13445 allow for use when elongation is over 12%
- API does not "fall in" under this paragraph, but you can use it as long as it meets certain requirements
- I am designing a pressure wessel consisting of a pipe with two end caps, for pressuring up "well-equipment" in that specific pipe, hardness and ID
- ppf = pounds per foot (e.g. wall thickness)

You don't really need to understand what I am doing, but I was just interested in on particular field of material science...

 

[XL83NL]

if I dont understand what youre doing (which could very well say something about me rather than you), then how would I be able to help you?

Furthermore, acc. para 4.1.4 of part 2 the minimum elongation shall be greater than or equal to 14%, with a few exceptions where it may be lower (but there's not mention of 12%).

Going to part 3, the maximum allowed values of the nominal design stress for pressure parts other than bolts is based on the materials Rp0.2 and Rm values. The yield you refer to is not in there.