Shaft service Life according to Standards 1

[Jugaado Engineer]

Hello Everyone,

I hope you are doing well. I am currently doing RCA regarding a shaft failure which was continuously in use for the past 10 years without any proper inspection maintenance plans followed regarding it. The last proper maintenance plan regarding shaft inspection was carried out in 2014 and in 2019 it was supposed to be inspected again but the plan was not followed. Now in 2024, this shaft broke resulting in a incident in our company. I was just wondering what is the normal service life of a shaft especially for a motor shaft. If anybody knows about any resources telling about the average service life kindly share those resources and your thoughts on it as well. Moreover if anybody knows about any ASME/API codes that specifically tell us about the average service life of a shaft?

I would really appreciate it if you guys can help me in this issue.

 

[Gr8blu]

The service life is a direct result of the torsional and radial loading on the shaft. Small perturbations at high frequency can result in damage over a shorter period than large perturbations at low frequency.

Case 1: Generator manufactured in 1892. Has run continuously (yes that's what I said) until INTENTIONALLY taken out of service in 2019. Shaft life in excess of 125 years.
Case 2: small misalignment to the driven resulted in abnormally high radial load applied with high frequency oscillatory torque to the motor shaft. Shaft lasted exactly 67 minutes after installation and commissioning was completed.
Case 3: large motor in metal rolling application. Had been in service for 38 years at the point in question. Jackshaft support between motor and driven equipment started to have excessive wear in a single "slipper" support (there were three on the jackshaft). Result was induced torsional strain at very high frequency. Once the high-frequency response started, the shaft lasted 97 seconds. The shear plane was across a point midway between the rotor core iron and the bearing - where the diameter was 1320 mm (52 inches).

Postscript: Fatigue life is affected by cyclic stresses, residual stresses, material properties, internal defects, grain size, temperature, design geometry, surface quality, oxidation, corrosion, etc. The fatigue life of a component under the following different fatigue mechanisms can be ranked from low to high as: thermal shock, high temperature low-cycle fatigue (LCF), low temperature LCF, and high-cycle fatigue (HCF). In the assessment of the risk of fatigue failure, it may be assumed that the component is safe for an infinite number of cycles if it does not show failures after more than ten million cycles.

The total fatigue life is equal to the life of crack formation and crack propagation. Fatigue life is dependent on the cycle history of the loading magnitude since crack initiation requires a larger stress than crack propagation.

The fatigue life of the component can be determined by the strain, stress, or energy approach. Fatigue is a very complex process affected by many factors. It is usually more effective to use a macro phenomenological method to model the effects of fatigue mechanisms on fatigue life rather than using a microscopic approach.

Converting energy to motion for more than half a century

 

[shvet]

for info

Appendix C
Some tips for accident investigators
Be prepared. When a process incident occurs, you should be ready to hit the ground running. Activating your investigation team and commencing established investigation protocols should be second nature.
Don’t set a target for dangerous incidents. If you do, people will find reasonswhy some should not be counted and the target will always be met.
Don’t look for culprits to blame. Today everybody says they don’t, but after an accident many revert to old ways of thinking. It will be nigh on impossible to convince your employees to report incidents if they know the modus operandi of management is to immediately seek the “guilty party” (see Chapter 28).
Try for an indulgent attitude to non-compliance. This is usually a price worth paying to find out what really happened. Remember that many violations occur because people are trying to help; they think they have found a better way of carrying out a task.
[Note: The two items immediately above are both important in developing a just culture that will facilitate a reporting culture (see Section 1.2.2). We acknowledge that progressive discipline can play a role in dealing with issues such as habitual, reckless behavior. Just be sure to ask why such behavior was tolerated to the extent that it became habitual.]
Keep your eyes and ears open and “lunch around.” To find out what has not been reported, don’t lunch with the same people every day (literally and figuratively).
If you are asked to approve claims for damaged clothing or overtime for cleaning up spillages, ask if the incident has been reported and investigated.
(See the quote by John Timpson near the end of Section 26.11.)
Always visit the site of accidents. Look where others do not, behind and underneath equipment. Look at neighboring areas for comparison.
Photograph the scene. Pictures will be helpful for inclusion in the report and for future use in safety courses and publications. A photograph may tell us more than a thousand words.

Taken from

https://a.co/d/iSj1TYZ

also maybe useful

https://www.hse.gov.uk/pubns/books/hsg245.htm

https://www.hsestudyguide.com/how-to-investigate-an-incident/#14_Common_Pitfalls_to_Avoid

chapers "Pump Failure Analysis" and "Failure Statistics and Component Uptime" in

https://a.co/d/elyPCaY

 

[NRP99]

Check thread404-469754.

ASME - ANSI B106.1M - Design of Transmission Shafting was used for shaft design earlier but is now withdrawn. But you can anyway use for reference purpose.

 

[geesaman.d]

Shaft life is notoriously difficult to estimate accurately when you have a dataset of 1.

B106.1 gives some very good methodology but it requires many inputs. Even simple things like exact surface finish, exact internal corner radii, actual material yield and ultimate strength, and corrosion keep this answer to only an estimate. Then there is the possibility of missing data such as high speed coupling misalignment. Hopefully when you've run your calculations, you get some useful information.

It usually comes down to common causes: preload, misalignment, misuse, inaccurate maintenance, corrosion, or simply specified incorrectly for the service.