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Welding of Pressure Vessels

The document discusses the economic considerations of welding pressure vessels. There are three main factors that determine the choice of welding method: 1) the circumstances of welding, such as accessibility of the joint, 2) requirements of welding codes which specify allowable joint types and stress values, and 3) economic aspects. Economically, V-edge preparations are cheaper than J or U preparations, double V joints use half as much weld metal as single V joints, and thicker plate with lower quality welds may be more cost effective than thinner plate with higher quality welds depending on the vessel size. Proper cost accounting considers factors like weld seam weight, filler metal, gas and electricity costs, labor costs, and duty cycle.

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343 views2 pages

Welding of Pressure Vessels

The document discusses the economic considerations of welding pressure vessels. There are three main factors that determine the choice of welding method: 1) the circumstances of welding, such as accessibility of the joint, 2) requirements of welding codes which specify allowable joint types and stress values, and 3) economic aspects. Economically, V-edge preparations are cheaper than J or U preparations, double V joints use half as much weld metal as single V joints, and thicker plate with lower quality welds may be more cost effective than thinner plate with higher quality welds depending on the vessel size. Proper cost accounting considers factors like weld seam weight, filler metal, gas and electricity costs, labor costs, and duty cycle.

Uploaded by

Dvida Pleasure
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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WELDING OF PRESSURE VESSELS – ECONOMIC CONSIDERATION

There are several methods to make welded joints. In a particular case the
choice of a type from the numerous alternatives depend on:

I. The circumstances of welding


II. The requirements of the Code
III. The aspect of economy

1. THE CIRCUMSTANCES OF WELDING


 In many cases the accessibility of the joint determines the type of
welding. In a small diameter vessel (under 18 - 24 inches) from the
inside, no manual welding can be applied. Using backing strip it must
remain in place. In larger diameter vessels if a man way is not used,
the last (closing) joint can be welded from outside only.
 The type of welding may be determined also by the equipment of
the manufacturer

2. CODE REQUIREMENTS
 Regarding the type of joint the Code establishes requirements based
on service, material and location of the welding.
 The welding processes that may be used in the construction of
vessels are also restricted by the Code as described in paragraph
UW-27
 The Code regulations are tabulated on the following pages under
the titles:
a. Types of Welded Joints
(Joints permitted by the Code. their efficiency and limitations of their
applications.) Table UW-12
b. Design of Welded Joints
(Types of Joints to be used for vessels in various services and under
certain design conditions.) UW-2, UW-3
c. Joint Efficiencies and Stress Reductions
(Efficiencies of joints at certain locations and reduced allowable
stress to be used in calculations of vessel components)
 The data of the table are based on the following Code-regulations:
full, spot, partial radiographic examination or no radiography of
A.B. and C joints UW-II
 For Longitudinal stress (calculation the efficiency of partially
radiographed joint is the same as for spot radiographed joints.
 Seamless vessel sections and heads with Category B, C or D butt
joints that are spot radiographed shall be designed for
circumferential Stress using a stress value equal to 80% of the
allowable stress value of materials UW-12(b)
 When the joints are not radiographed and for joint efficiency, E the
value, in column c of table "Types of Welded Join” arc used. In all
other design calculation stress value equal to 80% of the allowable
stress value of material shall be used except for un-stayed flat
heads, etc. UW-12(c)

3. THE ECONOMY OF WELDING


If the two preceding factors allow free choice, then the aspect of
economy must be the deciding factor.

Some considerations concerning the economy of welding:

 V-edge preparation which can be made by torch cutting, is always


more economical than the use of J or U preparation.
 Double V preparation requires only half the deposited weld metal
requited for single V preparation,
 Increasing the size of a fillet weld, its strength increases in direct
proportion, while the deposited weld metal increases with the
square of its size.
 Lower quality welding makes necessary the use of thicker plate for
the vessel.
 Whether using stronger welding and thinner plate or the opposite is
more economical, depends on the size of vessel, welding
equipment, etc, This must be decided in each particular case.

COST ACCOUNTING FOR WELDING WORK:


 Weight of welding seam,
 Costs of filler metal,
 Gas Costs,
 Fusion efficiency and welding speed,
 Labour Costs,
 Duty Cycle,
 Electricity Costs,
 Machine Costs,
 Standard Values.

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