Introduction to boilers and pressure vessels

What are Boilers and Pressure Vessels?

Boilers are closed vessels designed to heat water or produce steam under pressure for industrial applications such as power generation, chemical production, and ship propulsion.

Pressure Vessels are containers designed to hold gases or liquids at a pressure substantially different from ambient pressure. These are widely used in industries such as oil & gas, petrochemical, and food processing.

Key Differences Between Boilers and Pressure Vessels:

Aspect	Boiler	Pressure Vessel
Function	Generates steam or hot water	Stores fluids/gases under pressure
Design Code	ASME Section I	ASME Section VIII Division 1/2/3
Working Medium	Water, Steam	Gases, Liquids
Typical Pressure	15-3000 psi	15-10000 psi
Testing	Hydrostatic + Steam Test	Hydrostatic or Pneumatic

Applicable International Standards

ASME Boiler and Pressure Vessel Code (BPVC):

Section I: Power Boilers

Section IV: Heating Boilers

Section VIII: Pressure Vessels

PED 2014/68/EU: European Pressure Equipment Directive

EN 13445: European standard for unfired pressure vessels

API 510 / API 570: Maintenance & inspection guidelines

Basic Design & Calculation Principles

Thin-Walled Cylinder Stress Formula (When D/t > 20):

• Hoop Stress (σθ): σθ = (P * r) / t
• Longitudinal Stress (σL): σL = (P * r) / (2t)

Where:

• P = Internal pressure
• r = Internal radius
• t = Wall thickness

Thick-Walled Cylinder (When D/t ≤ 20):

Apply Lamé equations considering radial stress gradients.

Material Selection

Material Type	Example Grades	Applications
Carbon Steel	SA-516 Gr.70, SA-285	Low/medium pressure vessels
Stainless Steel	304/316/321/347	Corrosive fluids, food-grade vessels
Duplex Steel	S31803, S32750	Offshore, sour gas environments