?? Have you ever contemplated ASME Section VIII Div. 1 Subsection B, UW-2, which addresses Service Limitations? ??

In this article, we will look into the details about the service restrictions for :

• UW-2(a) Lethal services
• UW-2(c) Unfired Steam Boilers with Design Pressure exceeding 343 kPa (50 psi)
• UW-2(d) Pressure Vessels or parts subjected to Direct Firing

Let's get started,

UW-2(a): Lethal Service

Lethal service refers to substances that are poisonous gases or liquids of nature that a very small amount of the gas or of the vapor of the liquid mixed or unmixed with air is dangerous to life when inhaled. Either the client or its designated agent should provide the requirement if the service is Lethal or not.

In Designing pressure vessels for Lethal service, there are additional requirements that must be followed to ensure safety. In this, we will cover the additional requirements related to Lethal service in pressure vessels.

• All butt-welded joints shall be fully Radiographed

If the service is mentioned as Lethal, all but welded joints shall be fully radiographed. This is a requirement that must be mentioned in the drawing because it will be the final output. 100% radiography is required to ensure safety.

• ERW pipe or tube is not permitted to be used as a shell or nozzle

The code prohibits the use of ERW pipes or tubes for Lethal service. This is an important restriction that must be remembered.

• PWHT for Carbon or Low Alloy Steel becomes mandatory with few exemptions:

For every thickness of carbon or low alloy steel, PWHT becomes mandatory. PWHT stands for Post Weld Heat Treatment. This is a crucial requirement because it ensures the material's toughness and ductility after welding, which is essential for safety. There are exemptions to this requirement, but they must be checked if there is a specific requirement.

• Weld Joints of various category shall be as follows:

(-a) for lethal service, Category A type joints shall be of Type No. 1 which are essentially full penetration welds.

(-b) All Category B and C joints shall be Type No. (1) or No. (2)

(-c) Category C joints shall be made with stubs like shown below:

(-d) Category D joints shall be made with full penetration welds

UW-2(c): Unfired Steam Boilers

When it comes to unfired steam Boilers with a design pressure of over 50 psi, there are certain restrictions that must be followed.

• Category, A joints, Type No. 1 must be used
• Category B joints, either Type No. 1 or Type No. 2 shall be used.
• Butt-weld joint is used, it must be fully radiographed with some exceptions
• Additionally, if carbon and low alloy steel are used as the material, Post-Weld Heat Treatment (PWHT) is mandatory.

UW-2(d): Direct Firing

For vessels with direct firing, following conditions shall be met:

1.????? Category A , Type No.1 is Applicable.

2.????? Category B Type No.1 or (2) is applicable.

3.????? Vessels made of carbon steel with a thickness greater than 16 mm and material with P-No. 1, Post-Weld Heat Treatment (PWHT) is mandatory.

In conclusion, service restrictions are important considerations in design to ensure the reliability and safety of the welded joints.

Thank You…….

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