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Using older edition for replacement part 1

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shamrock138

Mechanical
Oct 15, 2007
13
Hello all,
Does anyone know if it is permissible, or an interpretation exists, for constructing a new part, a tube bundle for example, using an older edition of Section VIII Div. 1 for design? More or less for limited dimensions that would have to be met. If permissible, or such a code case exists, I would imaging that the material would have to use the properties and values of the older Section II. My gut tells me this is a long shot, but I am still posting it. Thank you in advance.
 
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shamrock138, tube bundles are often replaced "in kind" without worrying about Editions, etc. especially if drawings of the existing bundle are available.

Regards,

Mike
 
shamrock138;
Why would you consider using an older Edition of the ASME Code to manufacture a replacment part? The latest Edition of the Code, approved by your Juridsiction, is usually the route to go for most replacement parts. Why? Because as the Code committes gain expierence with newer and existing materials and designs, these enhancements soon become revisions, which improves the Code.
 
SnTMan, thank you for your reply. The whole tube side including the channel would be replaced, excluding the tubes and tubesheet. The bundle, only used as an example, would be the least of my problems. This is a large unit and body flanges and channel covers would increase in thickness, therefore increasing the length of the exchanger, in which I am very limited with dimensions.
 
metengr, thank you for your reply as well. I completely understand where you are coming from and totally agree. Unfortunately in my position I have people above me that want proof that I can not do it. That is why I brought up interpretations. I thought that would be my best bet.
 
shamrock138;
This type of work (replacement part fabrication and installation) should fall under the NBIC or API, and is not addressed in ASME B&PV Code directly. ASME B&PV Code is a construction code for new boilers and pressure vessels. It can be used to manufacture replacement parts in-kind or under an alteration using an in-service inspection, repair and alteration Code like the NBIC or API.

For either case, there is no requirement to use the original edition of the code of construction for fabrication of replacement parts. There is an interpretation for this in the NBIC (I can't recall at the moment what the interpretation number is for this). Original code of construction does NOT imply edition and addenda, it simply refers to the code of construction used for the item.
 
The NBIC Interpretation is NBI 95-19 and it also states that "Repairs and alterations may be performed to the edition/addenda used for the original construction or a later edition/addenda most applicable to the work." I suspect your problem may be related to the flange rigidity calculation, which became mandatory in 2007. If the exchanger was constructed to the 2007 code, I do not think you can utilize a code prior to 2007 for fabrication of the replacement parts.
 
You may have non-engineering reasons like liability. Yes, the original part built to an older code might have lasted X number of years so theorhetically the replacement would, but if the replacement ever let go and... well imagine the worst, you might be in for all kinds of liability especially if the newer code would have called for stronger components.

I did a project where a high pressure Hx with a 24" tubesheet designed and built in the '60's became a 27" thick tubesheet when it was replaced. That surprised me, but I took note. And to think, I had walked by that original unit many times in my life.

rmw
 
rmw;
I also have seen the opposite where components that were engineered to earlier editions of the Code had such large design margins that they still remain in service to this day!

This is not to say that current Code rules are less safe. What seems to have occurred over time is that fewer and fewer unknowns have been squeezed out and more FEA and other forms of analysis have allowed designers to sharp-shoot designs to the point where items can be predicted to be replaced. I myself appreciated the added margins used by our Code forefathers. However, in today's climate every penny counts and that means designs are to the ragged edge.

Bottom-line for replacement parts the designer needs to look at current rules and compare with past rules to decide what will be safe for service.
 
metengr, I strongly second your opinion on added margins. There is no cheaper insurance than a little extra steel.

Amazing advances in analysis, however our ignorance of actual field conditions is little changed.

Regards,

Mike
 
Metengr,

That is what surprised me about this top point heater in a supercritical plant at ~750 MW. When it was being designed and built, I was still designing and building stuff with a slide rule so I know its designers were too. I fully expected everything to shrink somewhat and even asked the engineers who did the calcs on the replacement (kitted it - reused only the shell and the channel and replaced everything else in between, tubes, tubesheets, zones, skirts, etc.) and as stated it went from a 24 inch TS to a 27 inch thick. That cost me 6" of surface on ~1500 tubes. The zones got larger, too. I was taken by surprise.

I have been involved in rerating stuff because when it was designed it had so much extra meat in it that with modern codes and calc methods, all that extra meat allowed a rerate.

So go figure.

rmw
 
rmw, I wonder if Part UHX contributed to your TS thickness increase. Applying it to existing equipment is troublesome.

Regards,

Mike
 
It has been several years ago that I had all that fun and if the designers told me the specifics I don't remember them, but it was a code calculation issue that drove the increased TS thickness.

rmw
 
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