Dollar Plate
Dollar Plate
(OP)
Can anybody give me a definition of a 'dollar-plate' as used for nozzle reinforcement, please?
This was offered by a Vendor with no further explanation, as if I was supposed to understand his defintion - I don't want to ask him and thus appear ignorant, especially if this is a common term in some parts of the world (not common in UK).
TIA
This was offered by a Vendor with no further explanation, as if I was supposed to understand his defintion - I don't want to ask him and thus appear ignorant, especially if this is a common term in some parts of the world (not common in UK).
TIA





RE: Dollar Plate
Vessel heads are usually formed with one plate section. But when the head diameter becomes too large and you cannot use just one plate section, the head is fabricated in orange peel sections. The orange peel sections meet at a "circular plate" at the center of the head. That circular plate is referred by others as the "dollar plate".
Is the nozzle that needs reinforcement located at the center of the head?
RE: Dollar Plate
Never hurt to ask. 99% of the engineering people at a vendor shop won't hesitate to answer your question, no matter how stupid it may seem to you and I. Those are usually the most enlightening questions.
RE: Dollar Plate
RE: Dollar Plate
Something for my spongy grey data bank (memory).
Thanks again.
RE: Dollar Plate
For a new vessel, I would rather prefer an insert nozzle like those in ASME VIII-1 Fig. UW-16.1 sketches (f-1) through (f-4) than a locally thick insert plate to compensate for nozzle reinforcement. I have only seen insert plates used in patching up holes in incorrectly located nozzles or in modifying nozzles in existing vessels. I am not saying insert plates (as nozzle reinforcement) cannot be used in new construction. It is just that in my few years of experience, I have not seen it done on a new vessel.
RE: Dollar Plate
FYI- the old silver dollars were our largest coin- minted up until 1935, then for a few years in the 1970's.
RE: Dollar Plate
Given a choice between an insert plate (the ones I've seen are typically rectangular, not circular) and a repad, I'll take an insert plate any day for a variety of reasons including strength/integrity (especially on a large repad one has to question whether the shell and pad are acting together) and inspectability (an external inspection using UT cannot "see" the shell thickness under a repad).
jt
RE: Dollar Plate
Our use of inserts is driven by our processes, one is extremely corrosive and the other is high temperature cycle driven.
The corrosive process likes crevices and will preferentially corrode nozzles by end grain attack. To mitigate the end grain attack we seal weld all penetrations to slow the corrosion and preventive the penetration of the space between the shell and the doubler plate. Another advantage of the insert plate is that is that the nature of our corrosion is intergranular. The product of IGC is a plethora of little notches in the shell that greatly enhances the the affect of any motion in nozzle. The additional thickness of the insert plate slows the process.
In the high thermal cycle process the doubler plate acts as a heat sink causing a higher differential between the shell and the doubler plate and the plate and the nozzle proper.
RE: Dollar Plate
100% NDE inservice inspection is one of the reasons
rhg
RE: Dollar Plate
RE: Dollar Plate
The inset nozzles or self-reinforcement nozzles shall be used for thick vessels (more than 2"), especially if it is under thermal cyclic conditions (Like Reactor).
RE: Dollar Plate
You seem to imply that some of our experienced colleagues above are the authoritative body in vessel design & construction.
Would you be kind enough to tell me the specific paragraph in ASME VIII (Div. 1 or Div. 2) where it is mandatory use insert plates or self-reinforcing nozzles. Your use of the word "shall" makes it seem mandatory. Let's assume the vessel is not in cyclic service.
doct9960,
I have seen project or client specifications where integrally forged nozzles (like those heavy forged butt-welded nozzles) are explicitly required on thick vessels or vessels in high temp hydrogen service. I don't have the ASME code handy, and maybe it is not really required by ASME, but I will try to give an opinion. For thick walled vessels, I think the reason is for NDE reasons. It would be difficult to perform NDE on a thick vessel with full penetration corner weld nozzles. For vessels in hydrogen service, I think it is because of hydrogen embrittlement or hydrogen induced cracking
RE: Dollar Plate
You could referee to ASME VIII DIV 1, Para UW-16C. The last paragraph is saying, "If additional reinforcement is required, it shall be provided as integral reinforcement as described in (1) below, or by the addition of separate reinforcement elements (plates) attached by welding as described in (2) below."
RE: Dollar Plate
Sorry I did not really answer your question. My answer is NO. I do not recommend a locally thick insert plate for heavy wall vessels(greater than 2" thick) or for nozzles in high-temperature hydrogen service.
RE: Dollar Plate
Also, using integral nozzles in accordance with UW-16.1 (f1-4) is required in case the radiography test will be implement. That is why this type is called ridoghraphable type.
RE: Dollar Plate
Thanks for the reply. I was trying to get some opinion or experiences from other experienced forum members, if they have actually used locally thick insert plates (for nozzle reinforcement purposes) on thick vessels or vessels in hydrogen service for new construction. My reasoning is why would you design a NEW vessel with insert plates when you could have thickened the entire cylinder/head section or have used an integrally reinforced nozzles. I believe that ECONOMICS is one of the reasons, perhaps the only reason, why some vessel manufacturers use insert plates (for nozzle reinforcent) on new vessels.
RE: Dollar Plate
As I posted above integral components we used were for elimination of a corrosion path and mitigation of the effects of extremely rapid thermal cycling. Enabling radiography was secondary. This fact that integral reinforcement enable radiography was not lost to us it was not paramount in our decision to use integral reinforcing in the design and fabrication of our vessels. In our case the ability to radiograph the resultant weld joint from the use of an insert plate or integral nozzle is just an added positive benefit. These designs are used are used for all new construction in these 2 areas along with several others where the problem isn't as severe.
In the corrosive process areas design criteria is based on elimination of flanges, welds, crevices and rigorous metal chemistry.
In the high thermal cycle process areas the whole design is based on minimizing all metal section changes. No doubler plates, going back to lap joint flanges, insert support pads, minimizing the section change in the shell. Every component uses the smoothest transition possible. All welds a planished. Eliminating penetrations of the vessel.
My involvement in the problems with process equipment started in the early 60's. I had many battles on which direction to proceed as most approaches I suggested profaned conventional wisdom of the era. The recognition by the code and pundits of it that problems will occur when you impose high thermal cycles on Austenitic SS Vessels sure made my job easier.
It addition to thermal cycling problems we encountered a pressure cycling problem in the H2 plant's purification system. We had a through wall seam failure in which I was able to get the cracked area for metallurgical evaluation. The failure mechanism was H2 assisted fatigue emanating from the toe of perfectly acceptable weld. Though this type of failure had occurred several times around the world there had been no metallurgical examination of any of the previous failures. This type of failure hadn't been considered in the design of other PSA vessels as we had just installed another train on a new second unit that had identical design as the failed one. We replaced the entire train with vessels designed based on thing we had learned in minimizing thermal fatigue.