Does the machining of the gasket surface (without welding) of a 12x16 steam drum boiler closure

[jeevesme]

Does the machining of the gasket surface (without welding) of a 12x16 steam drum boiler closure require an R-stamp?
We have a steam drum atop our #2 boiler the is leaking during the hydro. There is some corrosion on the closure that is causing it to get an inadequate seal.
The company that will be machiining the surface says that as long as they do not need to do any welding, there is no need for an R-Stamp.
I disagree. The NBIC states a Repair as: "The work necessary to restore pressure-retaining items to a safe and satisfactory operating condition.".
And a Mechanical Repair Method as: "A method of repair, which restores a pressure retaining boundary to a safe and satisfactory operating condition, where the pressure retaining boundary is established by a method other than welding or brazing, as defined under the rules of the NBIC.".

 

[metengr]

No, this particular case does not require an R-Stamp. Why? Because the 2013 Edition of the NBIC Part 3, Form R-1 Report of Repair (5.13.1)does not have a box for mechanical repairs. You can certainly describe a repair on a Form R-1 but it must have one of the repair options listed; welded, graphite pressure equipment (this is for mechanical repairs by the way), and FRP equipment. We on the NBIC have not decided on how to deal with mechanical repairs in lieu of welded repairs.

 

[GenB]

Machining is the same as you grinding the surface to make it flat. Taking just a little bit of metal won't hurt. If you take a big PC. You may have to check on required internal projection minimums. Else noR stamp required... Ask your local inspector.

 

[jeevesme]

Isn't it the intent of the code to make sure that any work done to a Code Stamped pressure vessel is adequate for service? Why wouldn't they address machining of a manway closure? If the machine shop took off too much material, there is a possibility of a catastrophic failure.

 

[racookpe1978]

Well, it would. If you were cutting off massive amounts from the strength-giving walls of a flange 2 inch thick, rather than machining off 0.060 off of the front face of a 3 inch thick flange to make the flange seal correctly. If the wall were lost, yes, the boiler would fail.

You need to understand the real world here, as well as the "code world" that is trying to safeguard innocents and bystanders from catastrophic internal boiler pressures. The "code" cannot prevent all errors, but rather can only write down ("codify" literally) a few absolutes.

 

[Duwe6]

It is hard to take off too much material on a typical oval manway ring - their thru-thickness is measured in inches. One round of machining for clean-up of moderate pitting or minor steam cut is known to not infringe on minimum thickness, thus no spot on an R-1. However, it does require documentation in the boiler file; at the second or third machining of the same M/W, thickness needs to be measured and calculation performed.

NOTE: unless PWHT will be required, replacing the M/W ring is typically cheaper than machineing an oval item, and leaving it with the necessary RA-125 to 250 'phonograph' finish after getting a clean-up of the defects.

 

[jeevesme]

I measured the thickness before and after machining and documented it in the file. I'm just baffled as to why the NBIC would not require the necessary calculations and R-Stamp for this.

 

[metengr]

Why? If you machine off too much material welding will be required to restore the sealing surface. The NBIC began with welded repairs because this ultimately affects the material properties of the item and, as such, must be done in a controlled and consistent manner.

Other types of repairs which do not alter the mechanical properties but affect performance are matters between the repair organization and user to decide.