Dollar Plate 2

[PPVE]

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

 

[doct9960]

PPVE,

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?

 

[vesselguy]

Another word for an insert plate which is much thicker than the local shell that it is being inserted in and butt welded to.
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.

 

[chaulklate]

I agree with vesselguy's definition. They are used to thicken the shell locally, very often around nozzle necks when sufficient reinforcement can't be achieved by a repad, whether it's for area replacement of the nozzle or to help counter other mechanical loads such as pipe loads.

 

[PPVE]

Thanks very much for your comments, guys. In the context of the Vendor's offer, the locally thickened plate for nozzle reinforcement is the answer I need, although it's interesting that another explanation exists within vessel engineering for a similar but different application.

Something for my spongy grey data bank (memory).

Thanks again.

 

[doct9960]

PPVE,

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.

 

[JStephen]

We use the term "dollar plate" to refer to any large round plate, in several different applications, without reference to any particular weld detail. Ask if it's not clear. (Maybe it's called a Pound Plate or a Euro Plate elsewhere?)

FYI- the old silver dollars were our largest coin- minted up until 1935, then for a few years in the 1970's.

 

[jte]

I've seen insert plates used on new construction typically for large nozzles with large loads. Most of the time a forging conforming to Fig. UW-16.1 (f1-4) will be cost prohibitive in large diameters, and the OD of the forging at the shell attachment will not be sufficient to handle the piping loads. Actually, I've seen very few such forgings in any size…

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

 

[unclesyd]

We use insert plates and insert nozzles essentially interchangeably on all new equipment. We trend to use insert plates on tanks and relatively thin wall PV's while insert nozzles are used on higher pressure PV's.
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.

 

[rhg]

Use insert plate por pressure vessels in lethal, corrosive or nucler service.
100% NDE inservice inspection is one of the reasons

rhg

 

[doct9960]

For nozzles in heavy wall vessels(greater than 2" thick) or for nozzles in high-temperature hydrogen service, would you recommend a locally thick insert plate to meet reinforcement requirements?

 

[Shofa]

As mentioned above the insert plate shall be used for reinforcing the nozzle for thin vessels and the thickness of the plate shall be thicker than the actual vessel thickness.

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).

 

[ukinam]

Shofa,
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

 

[Shofa]

Ukinam,

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."

 

[ukinam]

doct9960,

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.

 

[Shofa]

I agree with ukinam. Using locally thick inset plate for heavy wall vessels may create more local stress coming from thermal cyclic conditions due to the thermal differential between the materials.

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.

 

[doct9960]

ukinam,

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.

 

[unclesyd]

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.