Boiler and Pressure Vessel (BPV) Services Information
Boiler and pressure vessel (BPV) service providers specialize in the repair, rebuilding, maintenance, installation, and on- site construction of boilers, pressure vessels, piping, and safety valves. They may additionally provide cleaning, calibration, failure analysis, component testing, and part replacement services.
Boiler and Pressure Vessel Basics
Boilers are common devices for industrial heating and humidification applications. They consist of a fuel- or electric-powered energy source which heats water and/or generates steam. Hot water boilers are common in commercial applications such as comfort heating, dishwashing, and clothes laundering, while steam boilers are more often used to drive turbines for power generation as well as for industrial heating applications. Pressure vessels are typically defined as boilers or tanks designed to operate at pressures much higher than ambient pressure, typically delineated as greater than 15 psig.
All boilers are designed to include a heat source (furnace) and a heat exchanger — typically a system of tubes or piping — which allows water to be heated above its boiling point. They may use three separate designs to accomplish water heating:
Fire-tube boilers feed hot gases through tubes connected to the furnace. The tubes pass through a water-filled drum in order to transfer heat to the water.
Water-tube boilers feed water through a system of tubing. The tubing is surrounded by a boiler drum filled with hot gases from the furnace; the heat in the drum is transferred to the water tubing to generate steam.
Sectional boilers are constructed of several cast iron sections which are bolted together. Simple sectional boilers consist of a firebox which directly heats a corresponding water chamber.
A fire-tube (left) and water-tube boiler. Image credits: Citizendium | Energy Efficiency Guide for Industry in Asia
Boilers may also use one of several different combustion materials, including coal, biomass fuels, wood, gas, and oil. Other boilers may be heated by electric or hydronic (steam) methods. BPV service providers may indicate that they specialize in a particular type of boiler or heating method.
When water is boiled into steam, it expands rapidly and can travel through tubes or pipes at over 60 miles/hr (100 km/hr). While this results in an efficient means to transfer energy, it can also easily cause corrosion or scaling due to improper boiler operation or poor construction. This condition causes reduced steam quality, poor efficiency and, under worst-case circumstances, catastrophic boiler failure. Failure is also caused by overpressurization and insufficient water levels, the latter of which causes overheating and vessel failure.
When a boiler explodes, it rapidly releases large quantities of steam and scalding water that can cause extensive damage to nearby equipment or personnel. The failure of a large steam boiler with a water capacity of 10,000 kg would release the energy equivalent to 1,160 kg of TNT. Explosions have been a threat since boilers came into common use in the mid-19th century, with the deadliest boiler explosion in history — caused by multiple boiler failures and the resulting fires on the US steamboat SS Sultana in 1865 — claiming close to 1,800 lives.
Modern boiler manufacturers mitigate this risk by fitting their products with various safety measures, including:
Safety valves, which automatically activate under an excess pressure condition. They prevent overpressure by venting steam and other pressurized gases.
Various means of preventing low water conditions. These can include water columns, water gauges, low water alarms, and low water fuel cut-out.
Precise pressure measurement and management.
Blowdown valves to forcibly blow small amounts of water out of the boiler. This prevents high concentrations of water impurities that can cause scale deposits and corrosion within the steam generation system.
Diagram showing various boiler safety measures, including valves and pressure measurement devices. Image credit: Allied Heating and AC
The ASME Boiler and Pressure Vessel Code (BPVC) is the largest and most comprehensive standard published by the American Society of Mechanical Engineers (ASME). This standard provides guidelines for the design, fabrication, and inspection of boilers and pressure vessels to ensure that said products have long, safe service lives. The BPVC allows service providers to be certified in the fabrication and maintenance of specific boiler and pressure vessel types, and classifies such providers by letter. The standard defines the following boiler categories:
- A - power boiler assemblies
- E - electric boilers
- H -- heating boilers
- HLW - potable water heaters
- N - nuclear applications
- PP - pressure piping / fittings
- RP - composite / fiber reinforced pressure vessels
- S - power boilers
- T - transport tanks
- TD - pressure relief devices on transport tanks
- U/U2/U3 - pressure vessels (U) / specialized pressure vessels (U2) / high pressure vessels (U3)
- UD - pressure vessel rupture discs
- UM - miniature pressure vessels
- V/NV/UV/UV3 - safety valves for nuclear (NV), pressure vessels (UV), high pressure vessels (UV3), etc.
Until 2013, ASME issued individual stamps for each certification type; the organization now uses a universal stamp with a specific certification designator based on the categories above. An example of the new certification is shown below.
Image credit: ASME
BPV service providers may advertise specific services, specialties, or capabilities. Many of these services can be combined; for example, a service provider may provide on-site welding services.
Code welding - any welding services that comply with applicable BPV codes.
Compliance/certification - assessments for compliance and certification of new or upgraded boilers, repaired equipment, and safety devices. Many service providers provide assistance with ASME compliance, while others may concern codes such as OSHA and EPA.
Field/on-site - service providers have the capabilities, personnel, and/or equipment for on-site fabrication or repair. Some companies specialize in the installment/start-up work of new or repaired boilers; some also provide on-site training and testing with this service.
Material specification - the capability to specify and select materials compliant with ASME BPVC Section II - Materials. Service providers may have the ability to test and analyze materials to ensure compliance and material quality.
Off-site - work is primarily completed in the service provider's shop. New boilers are typically fabricated and packaged on a skid to be transported to an intended site. Equipment to be repaired must be disconnected and shipped to the designated repair shop.
Overhaul/rebuild - the capability to completely overhaul boilers and components, which is often an effective alternative to purchasing a new unit. Companies specializing in this service may be granted an 'R' (repair) certification from the National Board of Boiler and Pressure Vessel Inspectors (NBBI).
Training/interpretation - suppliers provide training services related to operation, maintenance, and compliance.
The location of a BPV service provider is important to consider. For overhauls or new builds, plants that contract with BPV companies must be prepared to incur shipping, transportation, and/or travel costs, which may vary depending on the location of the service provider and the plant. Likewise, repairs contracted to off-site companies must be disassembled and shipped. Due to the size and complexity of many industrial boilers, selecting a company within reasonable proximity is often advantageous.
Boilers may be fabricated, tested, and repaired according to many different standards in addition to ASME's BPVC described above. The American Petroleum Institute (API), British Standards Institution (BSI), and the Pressure Equipment Directive (PED) are responsible for other common boiler and pressure vessel standards. Some well-known examples include:
- AP I RP 573 - Inspection of fired boilers and heaters
- API 510 - Pressure vessel inspection code
- BS PD 5500 - Unfired fusion welded pressure vessels
- EEC/97/23 - Pressure Vessel Directive
Citizendium | Energy Efficiency Guide for Industry in Asia | Allied Heating and AC | ASME