Gordon Heaton
Titanium
- Joined
- Feb 19, 2007
- Location
- St. George, Utah
Good Morning.
At my place of employment we fabricate a product that is exposed to all manner of climatic stress. This particular query relates to wind-induced cyclic stress on a solid mild steel/stainless steel shaft. I cannot post a photo or drawing of the actual product, but I can give you a simple and very similar analogy: Think of it as a common weather-station sensor array. In our case, there is a base section made from ordinary sch-40 steel pipe which varies in diameter by application. One end of the pipe is firmly attached to a ground-mount set in concrete, and the other end has a female thread into which the solid steel/stainless steel 'stinger' is screwed. Atop the stinger is the wind-affected package.
Let's say the lower pipe size is 1 1/4" X 72" long, and the solid stinger is 5/8" X 48" long. (All production combinations were contract-engineered for wind load, but not for repetitive 'sway') In a proper installation, the sway is absorbed by the lower and upper sections together. The problem we face now was caused by the municipality installing the array, when they disregarded the instructions and cut the lower section from the specified length to very, very short. Around 12"-18". The stingers are work-hardening and fracturing, not at, but just above the thread where they are mated to the pipe. The wind load is not applied at the tip of the stinger. It is applied along the entire length, more like a distributed load.
The current stingers are 304L solid rounds. These were formerly made from 1018 and powder-coated. We switched to SS because of the added labor involved in fitting bearings where needed over powder coat. In the thread about forming an aluminum mast, DiggerDoug posted this link:
What is Fatigue Limit - Fatigue Strength - Definition | Material Properties
On that web page is a graph (2nd one down) showing relative benefits of various materials. Titanium is not feasible, 4340 would be fine. I've been trying to find a similar comparison showing 304L and 1018 but haven't yet been successful. Like every thing else, there are a hundred variables, most of which are way outside my ability to evaluate, so I'm looking for general tips and suggestions.
Yes, the problem was cause by the installer not following directions but they want it to work the way it is, and we're hoping to find a way to help make it happen. We like to keep our customers happy and our reputation excellent, so... what do you think? -Forgot something: we cannot increase the diameter of the stinger.
At my place of employment we fabricate a product that is exposed to all manner of climatic stress. This particular query relates to wind-induced cyclic stress on a solid mild steel/stainless steel shaft. I cannot post a photo or drawing of the actual product, but I can give you a simple and very similar analogy: Think of it as a common weather-station sensor array. In our case, there is a base section made from ordinary sch-40 steel pipe which varies in diameter by application. One end of the pipe is firmly attached to a ground-mount set in concrete, and the other end has a female thread into which the solid steel/stainless steel 'stinger' is screwed. Atop the stinger is the wind-affected package.
Let's say the lower pipe size is 1 1/4" X 72" long, and the solid stinger is 5/8" X 48" long. (All production combinations were contract-engineered for wind load, but not for repetitive 'sway') In a proper installation, the sway is absorbed by the lower and upper sections together. The problem we face now was caused by the municipality installing the array, when they disregarded the instructions and cut the lower section from the specified length to very, very short. Around 12"-18". The stingers are work-hardening and fracturing, not at, but just above the thread where they are mated to the pipe. The wind load is not applied at the tip of the stinger. It is applied along the entire length, more like a distributed load.
The current stingers are 304L solid rounds. These were formerly made from 1018 and powder-coated. We switched to SS because of the added labor involved in fitting bearings where needed over powder coat. In the thread about forming an aluminum mast, DiggerDoug posted this link:
What is Fatigue Limit - Fatigue Strength - Definition | Material Properties
On that web page is a graph (2nd one down) showing relative benefits of various materials. Titanium is not feasible, 4340 would be fine. I've been trying to find a similar comparison showing 304L and 1018 but haven't yet been successful. Like every thing else, there are a hundred variables, most of which are way outside my ability to evaluate, so I'm looking for general tips and suggestions.
Yes, the problem was cause by the installer not following directions but they want it to work the way it is, and we're hoping to find a way to help make it happen. We like to keep our customers happy and our reputation excellent, so... what do you think? -Forgot something: we cannot increase the diameter of the stinger.