How to go about Setting the Most Economic Steam Trap Maintenance Inspection Frequency in a Chemical Process Plant

If you wait for months to spot a passing steam trap it means you will have a lot of wasted steam and lost money. This is where the cost of wasted steam estimate lets you chose the better maintenance strategy for the business.

 


 

Hi Mike.

I am student on a mechanical engineering placement year on a chemical plant. I have been given the duty of setting up a routine for maintenance of steam traps. I just wondered if you have ever heard of any company that extends their policy on steam traps beyond surveying them now and then and replacing/repairing failed ones. If so then what do they do?

 


 

Hello Friend,

Thank you for your question on steam trap inspection and maintenance scheduling.

Can I suggest that the first task you must do is to learn what are the causes of steam trap failures in the operation. You need a good feel for why steam traps fail in that business. While doing the investigation you should segregate the analysis by steam use in a process and area of plant—it might show up some sort of currently hidden correlation while still permitting you to do a business-wide analysis.

You can look for information on why the steams traps failed and the dates they failed in the maintenance work order records and the operations daily shift records. If you cannot find the failure dates then use the date the work requests/ work orders were raised—they will not be the true failure dates but it is all that you have which is certain. If there is insufficient description to identify a failure cause for each steam trap failure then the analysis loses much of its value. You also need to talk to the fitters and operators who have worked in the operation a long time and find out what steam trap problems they have seen over the years, where they happened and their frequency. Talk to the operations and maintenance supervisors as well, since they are often long serving employees and they also have the desire to minimise production problems and will support any initiative that does that.

Using the work request/work order dates you can plot a timeline of the steam trap failures and replacement in each process/area across the years and look for patterns and frequency of failures/replacements. Look for evidence of early life failure which implies bad installation practices, or bad manufacturing, or wrong trap/material selection, or high contamination in the steam circuit, etc. Early life failure shows up as unbelievably short times between replacement/repair and the next failure. Steam trap designs have typical design lives which the manufacturer can tell you. If steam traps fail too often too quickly after installation it makes you suspect infant mortality failure causes.

Secondly you need to work out the cost of steam loss through a passing steam trap. What quantum of moneys does a day of wasted steam through a passing steam trap cost the company? That is a very important question to answer because it will drive economically sensible decision making. Until you can talk about how much money a maintenance strategy can save a company you can never be sure that you have chosen the right maintenance solution for the business.

Thirdly you need to identify if steam trap failures in each process/area are age related or occur randomly. Steam traps can fail from designed use in service as the stresses of usage accumulate, i.e. they failed through fair wear and tear as was intended by the designer. If most steam traps suffer age and usage related causes then replace all steam traps in a process/area on a fixed time interval based on the period that failures start to happen. When you plot the distribution of steam trap failures in a process/area you will see if there is a regular ‘age’ at which failures tend to start.

You can see an example of this failure analysis approach used for mining truck tyres at Do a Timeline Before Weibull Analysis article.

Steam traps can also fail randomly due to sporadic process problems and other random causes like debris in the steam system, water hammer, pipe stress, etc. If the causes of steam trap failure are mostly random then detection of individually passing traps by observation is used. This is a condition monitoring activity where replacement is done once there is evidence of failure. Usually the condition monitoring method is acoustic headsets listening for passing steam. A steam sight glass can also be inserted in the pipeline downstream of the trap and when continuous passing is observed a work request is raised. It is also possible to mount sensors that monitor continuously and alarm when the trap passes.

You could also do a Weibull analysis if you can model individual failure modes for the steam traps in each process/area and you have a minimum of eight to ten data points for each failure mode.

Setting the inspection frequency to check for randomly passing steam traps will be based on the historic information you have collected. If the inspection frequency is daily then you will find a passing steam trap quickly. Hence why it is best if operators inspect steam traps on a daily round and do not leave it to maintenance fitters on a three monthly route. If you wait for months to spot a passing steam trap that means you will have a lot of wasted steam and lost money. This is where your cost of wasted steam estimate lets you chose the better maintenance strategy for the business.

It would be easy to develop a spreadsheet cost model of your inspection options and price up the cost of wasted steam for each one based on the range of viable scenarios that can happen in the business. If the daily cost of wasted steam from a passing steam trap is expensive it might even be financially sensible to subcontract the steam trap inspection to someone who comes in every day for half a day to find passing steam traps. It is the economics of the situation that drives the steam trap inspection strategy. What everyone else in the industry does has got nothing to do with what is right for your company.

If you go immediately into setting up a preventive maintenance route where people observe every steam trap on a set frequency you cannot be sure that it is an optimal solution. By doing the above level of analysis before choosing the maintenance strategy for the process/area you will be confident that you deeply understand the situation and its complexities so that the choices you make are economically optimal for the business.

If you have further questions on the analysis please feel free to ask me.

 

My best regards to you,

Mike Sondalini
Managing Director
Lifetime Reliability Solutions HQ

 

PS. If you require advice on industrial asset management, industrial equipment maintenance strategy, defect elimination and failure prevention or plant and equipment maintenance and reliability, please feel free to contact me by email at info@lifetime-reliability.com

 

The CEO, Executive, Manager, and Engineer Who Wants Their Enterprise Asset Management and Maintenance Systems to Get World Class Reliability and New Profits

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