How to calculate Tmin for steel chimney in service for 40 years?

[sxz]

Hi, Steel Chimney Experts,
I like to know what conditions should be considered to calculate the minimum required wall thickness (Tmin).
1) Original wind code
2) Original nominal wall thickness, instead of actual wall thickness measured.
3) Original allowable tensile stress
4) Original allowable compressive stress

Thanks in advance for any advice.

SXZ

 

[PSSC]

This answer will not be very helpful I am afraid.
I can't give you a how-to but maybe some places to start reading.

Is this being compared to API560 or STS-1?
There are plenty of older articles written on the design of steel stacks out there for you to read if neither of these are being considered. I believe Bednar's book has some good examples of how things were done in that era.
I would not use API560's method of determining the natural frequency, it is overly simple in my opinion. ASCE has two books about petrochemical equipment, one for wind, one for seismic. Both use a good method to find the natural frequency of the stack/vertical vessel.
Your main concern will be the it's natural frequency and it's reaction to certain wind speeds in regard to vortex shedding.
But again, if it's still standing after 40 years it's probably good regardless if it passes some nice equations we use to approximate the stresses it will see.

It all really depends on what the customer is looking to find out.


1) I am not sure what wind code you would use, that would have to be agreed to by the customer.
ASCE7 first was published in 1988 so it was probably done to the internal specs from the original engineering company. But I don't know how you would find that. Many companies had their own wind calcs back then. Again Bednar has a section on this.

2) I would use the current wall thickness if you have it. It should have a corrosion allowance, based on whether or not it is internally lined.

3)/4) Tensile strength is usually not the main concern but should be checked. The compressive allowable stress on a thin wall cylinder is almost always the limiting factor.


I would start with API560 and ASME STS-1, read those and you will have more questions than answers but at least better questions.

 

[sxz]

PSSC, Thanks for your time for response.
I applied Compress to check it with original nominal thickness, Tmin is less than the measured wall thickness, it passed.
If input of measured wall thickness, a thicker Tmin is more than the measured, it failed.
This is different from the evaluation on the old pressure vessel, which has NBIC and rules from local authority. For steel stack, is there any rules to evaluate the stack's Tmin in service.

 

[WARose]

Hi, Steel Chimney Experts,
I like to know what conditions should be considered to calculate the minimum required wall thickness (Tmin).
1) Original wind code
2) Original nominal wall thickness, instead of actual wall thickness measured.
3) Original allowable tensile stress
4) Original allowable compressive stress

I'm not sure I follow your question(s). Are you looking at a stack based on a modification to it? If so, I can't imagine why you would (for example) really care about the "original" thickness vs. the measured thickness. (Unless you think the measured thickness is off.)

In any case, in addition to the resources recommended......let me also add 'Tubular Steel Structures: Theory and Design', 2nd ed, by: M.S. Troitsky. I bought it at The James F. Lincoln Arc Welding Foundation back in the day.

It has a Chapter on self-supporting stacks. (Including a check procedure on vortex shedding.)

For external loads.....the combined stresses should probably be checked by Bednar's book on pressure vessels and/or the Bergman paper. (I.e. 'The Design of Vertical Pressure Vessels Subjected to Applied Forces'. From what I understand: a fairly well known paper in mechanical engineering circles.)

 

[sxz]

Thank you, WARose, I have the book, Tubular Steel Structure. It gave a critical allowable stress, about 40%Fy. In Compress, I use chart of CS-3, if the input thickness is thicker as nominal, Compressive stress (B) is higher (22% Fy), then Tmin is smaller. If input of thickness is actual one, B will be smaller (17% Fy), Tmin will be thicker than that calculated with nominal thk input.

 

[StructEngBrah]

It's hard for us to know exactly what COMPRESS is doing without seeing the output. I think it's important for you to go through the detailed calculations that COMPRESS is doing to get a better understanding. I have some limited experience with COMPRESS, but I always found the output and calculations to be very easy to follow. They provide code references back to exactly what it is doing. It's a good idea to always understand the input and output of any software, but COMPRESS is extra black boxy to me compared to other software. Be careful with it and make sure you understand what it is actually doing.