Difficulty with clad header boxes

[kevlar49]

I have tried specifying alloy clad header boxes for air coolers, but have received resistance to doing that. I have asked why this cannot be done, but have not understood the constraints. Can someone with fabrication experience explain why would it be so difficult to weld clad plate to form a clad header box? I always thought that the root pass could be easily made with enough alloy filler to avoid dilution with subsequent passes made with carbon steel.

Being able to use clad plate instead of carbon steel would greatly reduce the cost of the exchanger.

 

[metengr]

kevlar49;
Your suggestion is quite valid and is done routinely. Roll or explosive bond, sheet or weld cladding applications on plate material is done to reduce material costs by providing the same corrosion resistance results as if using a solid plate of the corrosion resistant alloy (CRA). The only possible exception I could think of to shy away from cladding are physical or geometrical constraints of the object.

 

[SnTMan]

kevlar49, the issue may be with closing out the header. It would be preferred to have access to both sides of the welded joint to 1) make the base metal weld, and 2) gouge and restore the clad. Difficult to do properly from one side only, although it can be done. How to NDE?

Also do you have a plugsheet? What do you do with it, overlay inside the holes before tapping?

Having recently checked clad plate prices, it is not necessarily cheaper than solid 304 for example, although you don't say what your alloy is. Lead times are forever.

Maybe further question your vendors to see what the concerns are?

Regards,

Mike

 

[ElfEiken]

If you only have access to the carbon steel side, you have to weld the cladding first, with suitable stainless steel. However, since you cannot weld using carbon steel electrodes on stainless, the whole weld would have to be with stainless steel.

Clad plate was also hard to get in small quantities when I worked for a fabricator. Only exception was when a large clad vessel was being constructed, you could order more by increasing the size or number of plates on the larger order.

Main justification for clad is the stability (valve slide plates, where solid stainless would distort on final grinding) or vessels where the higher allowable stresses of the carbon steel backing allow a thinner wall tha solid SS.

 

[deanc]

Depending on your base metal/cladding/dimensions and thickness the fab shop may be limited on forming capablity.

How many nozzles do you have? Lots of little sensor couplings?

Some materials require "clean" forming equipment,if it is a "steel shop" this will be a problem.

I have also seen clad material separate when formed. Cost?
Have not had the problem with the explosive bonded. But sometimes size limited and you need to trim away the outside edges after the blast.

So this along with the welding is a problem.

How much do you wish to pay?

 

[thermmech]

I feel that SnTMan's comments are right on the money. Tipically, aerial cooler header boxes (I am making an assumption here now that we are talking about them) are very hard to weld / assemble if plates are clad.

The only way to properly do welding of these header boxes is if their construction is not plug box but cover plate type.

Manufacturers will resist doing clad construction and quote only solid SS boxes for plug type headers.