Multilayer Vessels

Multilayer vessels Multilind Multiload-375 Multiload Mark II Multilure... 

Because of the possibility of voids between layers, it is preferable not to use multilayer vessels in applications where they will be sub-jec ted to fatigue. Inward thermal gradients (inside temperature lower than outside temperature) are also undesirable. 

Multilayer vessels are made by wrapping several layers of relatively thin plate round a central tube. The plates are heated, tightened and welded, and this gives the desired stress distribution in the compound wall. The vessel is closed with forged heads. A typical... 

The term solid-wall or monobloc vessel is applied to all components where the cylindrical wall consists of a single layer. Solid-wall vessels are suitable for all types of pressure vessels, in particular for those operated under high temperatures. Thermal stresses arising during heating or cooling are smaller than in multilayer vessels because of the good thermal conduction across the wall. Therefore solid-wall vessels are especially suitable for batchwise operation. 

Only vessels for small units are completley made of corrosion- resistant material. This protection method is to expensive for large vessels. They can be more economically protected by a liner of corrosion-resistant material containing Mo, Cr, Ni and V. Multilayer vessels require corrosion-resistant steel only for the innner layer. They are often equipped with venting channels, so-called Bosch-holes to ensure that for example hydrogen diffusing through the inner layer is drained and could be analysed. 

Fig. 4.3-19. Different kinds of flanges of multilayer high pressure vessels [34]. a, forged flange shrunk onto the multilayer vessel body b, forged thinner flange ring shrunk onto the multilayer vessel body c, flange made out of the same material as vessel body d, forged flange ring welded directly to the inner liner of the multilayer vessel.

Multilayer vessels Mul blind Mulbload-375 Multiload Mark II Mulblure... 

Typical U.S. materials for solid-wall ammonia converter shells have been A516 Gr. 70, A212 Gr. B and A302 Gr. C (Mn-Mo-Ni) and nickel-vanadium steel for multilayer vessels. For similar conditions, most European fabricators have selected alloy material WSB 62, 24-CrMo 10 and Ducol W30, for example. 

A multi-layer vessel is a vessel in which the cyhndrical portion is made up of two or more contacting bands or layers. The inner shell is the innermost band of a multilayer vessel and is made in the same manner as any solid wall vessel. The inner shell can be of any suitable material to resist corrosion by the contents. This is one of the unique advantages of a multi-layer vessel. Subsequent layers are added on top of this inner layer by a variety of techniques to achieve the ultimate wall thickness required. 

In total, it is entirely probable that over 20,000 multilayer vessels have been fabricated over the past 80 years, many of which are still in operation. 

High residual stresses from welding cannot develop across the multiple thin layers in multilayered vessel shells. Any through thickness welds such as girth seams and nozzle welds do not develop high residual stresses because there is little shear transfer between tbe layers. As such, PWHT is seldom used and not desirable. 

Nozzle attachments to high pressure vessels are almost always made through the heads, or end closures, rather than through the shell as is done in common pressure vessels. This is primarily due to the thickness of the shells and the fact that multilayered vessels are common in high pressure systems. Nozzles through multilayer vessels, while not impossible, are discouraged. 

MULTILAYER VESSELS WITH SHRINK-FITTED SHELLS... 

Multilayer Vessels with Shrink-fitted Shells 297... 

Multilayer Vessels with S rink-fttted Shells 299... 

Example Co IculoHon 15.5. The interferences for the multilay vessel d ribed in Example Calculation 15.1 will be determined. The nominal diniensions of the three-layer vessel from Example Calculaticm li.l are ... 

Design the shell of a two-shell shrlnk-a mbled multilayer vessel nsing this st I. 4 he vessel is to have an inside diameter of 24 in. and is to operate at a pn ssure of 20,000 j i. The service temperature is to be under 600° F, and an allowable tensile strips of. 30,000 psi is to be used. 

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