Nominal Thickness for Clad Material Plate

[azmirosman]

Dear All,

Good Day,

I have question regarding nominal thickness definition for cladded plate.

For example ,the plate thickness of CS is 36mm and clad thickness is 3mm.

The nominal thickness of the plate will be 36mm (exclude clad portion) or 39mm (include clad portion)?

Thank you in advance

 

[GD2]

Which code you will use?

GDD
Canada

 

[azmirosman]

Hi GD2,

I'm using ASME Sec VIII Div.1.

 

[Christine74]

Be careful with this as there is no set definition, but the term "nominal thickness" generally refers the ordered plate thickness inclusive of the corrosion allowance (if any) and clad thickness (if any). It's used for things like calculating the vessel weight and as a baseline for subsequent UT thickness readings

In your case 36 mm would typically be called the "base metal thickness."


-Christine

 

[SnTMan]

Then there is whether base metal and clad thicknesses are ordered / supplied as "nom" or "min".

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[GD2]

azmirosman,
The minimum design thickness for cladded plate(integral or weld metal overlay) shall be the base plate thickness plus the cladding thickness. The ordered plate thickness, which is nominal thickness, shouldn't be thinner than the design thickness.
In your case, the nominal thickness should be 39 mm.

GDD
Canada

 

[Geoff13]

It will depend just what you are trying to decide based on the "nominal thickness".

My experience is that the cladding is only for corrosion allowance, and thus UCL-23(b) applies. This paragraph recognizes that if you order 39 mm composite thickness with 3 mm of cladding the actual clad may exist within the 36 mm base metal thickness, but this is permitted for a "reasonable" amount of cladding without any reduction in the base metal allowable stress even when the cladding material is weaker.

For selecting the PWHT, UCL-34(a) only requires the ordered base metal thickness to be considered. For deciding if the base metal requires impact testing UCL-27 only requires considering the ordered base metal thickness.

The mills will supply and price the material very differently depending on how you specify your thicknesses. For instance, SA-263 para 11.4 permits much larger overruns on clad plate than SA-20 para 14.2. This may not matter on a single small vessel, but can have significant impact on multiple shop built vessels or a large, field erected vessel (extra welding, shipping and lift weight, etc). You can specify nominal thickness (underrun permitted as per the standard Code rules) or minimum thickness (extra $ and weight) for either the base, clad or composite thicknesses. You can specify base thickness plus clad thickness, or composite thickness including clad thickness.

Weld procedure selection for the base metal will only depend on the base metal thickness, but my Code knowledge can't point you at the applicable paragraphs.

Part UCL will be your guide on most items.

Good luck
Geoff

 

[azmirosman]

Dear All,

Thank you very much for the explanation.

Dear Geoff,

I am trying to decide to use ASME Div.1 or Div.2.

In my company specification,any 'nominal thickness' of the plate more than 38mm,that vessel shall be designed using Div.2 instead of Div.1.

Since the supply plate thickness is 36mm for CS part,it will not require to design to Div.2.

However,after adding 3mm of clad material,the overall thickness plate became 39mm which is more than 38mm.

Therefore,currently i am evaluating several proposal from fabricator and some of them proposed Div .1 and there is several proposed Div.2.

I need to confirm if clad thickness shall be considered in nominal thickness since if corrosion allowance thickness need to be included in nominal
thickness.

Thanks

 

[Geoff13]

Since the specification is unclear you'll have to ask the writer what was intended for clad plates.

I could tell you my guess, but a guess from a stranger on the internet about what the writer might intend in a specification that only you have wouldn't be a very useful guess.

Geoff

 

[GD2]

azmirosman,
Just make sure that the clad material satisfies requirement of Para UCL-11 to be considered in the design thickness.

GDD
Canada