Codes for boiler control systems and pressure vessels

The end user is ultimately responsible to use the correct code for pressure sensors and transmitters for boiler controls and pressurized vessels.

02/13/2014


Figure 1: AST 4600 Pressure Transmitters from American Sensor Technologies are explosion-proof transmitters with a 1/4-in. male NPT port, a very popular fitting used in boiler tubing and piping systems. Courtesy: www.astsensors.comPressure sensors and transmitters are extensively used in pressure vessels and boiler systems to monitor fuel, steam, water, and air pressure. These sensors perform safety and control functions within the plant to maintain a safe environment with maximum performance.

Sensors in these applications are typically connected to the process via a threaded connection that allows liquid or gas to be measured in a leak-free condition. To retain the pressure at operating and overload conditions, the pressure port must be able to handle the operating pressure and temperature conditions.

See Figure 1 for a typical pressure sensor with ¼-in. male national pipe thread (NPT) port, a very popular fitting used in boiler tubing and piping systems.

ASME B31 code

The ASME B31 code for pressure piping is a very popular boiler code; it covers power piping, fuel gas piping, process piping, pipeline transportation systems for liquid hydrocarbons and other liquids, and refrigeration piping, as well as heat transfer components and building services piping. Prior to ASME B31, this code was known as ANSI B31.

Within the B31 code are many subcodes that define the exact application and use of pressure sensor fittings and ports that are allowable under the code. The widely used codes include:

  • B31.1- Power Piping for industrial plants and marine applications. This code prescribes minimum requirements for the design, materials, fabrication, erection, test, and inspection of power and auxiliary service piping systems for electric generation stations, industrial institutional plants, and central and district heating plants. It also covers boiler external piping for power boilers and high-temperature and high-pressure water boilers in which steam or vapor is generated at a pressure of more than 15 psig.
  • B31.3 - Process Piping for use in chemical & petroleum plants, refineries processing chemicals and hydrocarbons, water and steam. The code contains rules for piping found in petroleum refineries; chemical, pharmaceutical, textile, paper, semiconductor, and cryogenic plants; and related processing plants and terminals. The code covers requirements for materials and components, design, fabrication, assembly, erection, examination, inspection, and testing of piping handling fluids, gases, steam, and air. Pressure sensors with either male or female process ports are covered under this code whenever the pressure is more than 15 psig.

Pressure port design considerations under B31.3

The B31.3 code is intended for manufacturers, users, constructors, designers, and others concerned with the design, fabrication, assembly, erection, examination, inspection, and testing of piping, plus all other potential governing entities.

All pressure sensors employ some form of a diaphragm that is either machined from one piece of metal or welded or O-ring clamped as a two-piece assembly. This section of the pressure sensor is the thinnest and most sensitive of all components.

Figure 2(a) shows a one-piece thick 0.022-in. diaphragm while Figure 2(b) depicts a welded thin 0.001-in. thick diaphragm. Together, with the thickness and the type of metal, the operating pressure and operating temperature range dictate the safety conditions under which the pressure sensor can operate.

Figures 2a and 2b: Figure 2a shows a one-piece-thick 0.022-in. diaphragm while 2b shows a welded thin 0.001-in. thick diaphragm; both are used in the construction of a pressure transmitter. This section of the pressure sensor is the thinnest and most sensFigures 2a and 2b: Figure 2a shows a one-piece-thick 0.022-in. diaphragm while 2b shows a welded thin 0.001-in. thick diaphragm; both are used in the construction of a pressure transmitter. This section of the pressure sensor is the thinnest and most sens

Stresses and quality factors (for welded diaphragms only) are other important design considerations taken into account under B31. Metals such as strain hardened A-479-316L stainless steel level 2 need to be impact tested when used below -20 F. The impact tests must conform to B31.3 Table 323.2.2.

When sensors are constructed from metals such as N07718 (Inconel 718) and N10276 (Hastelloy C276) that offer temperature resistance from -325 F to +300 F, no impact testing is required.

Based on the calculations and thermal limits for the metals as required by B31.3 code, below are samples of calculations needed to determine the correct diaphragm thickness for a one-piece pressure sensor designed free of welds. Each sensor material has different containment capabilities based on the material properties and exposure to temperature.


<< First < Previous 1 2 Next > Last >>

No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
2016 Engineering Leaders Under 40; Future vision: Where is manufacturing headed?; Electrical distribution, redefined
Strategic outsourcing delivers efficiency; Sleeve bearing clearance; Causes of water hammer; Improve air quality; Maintenance safety; GAMS preview
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Flexible offshore fire protection; Big Data's impact on operations; Bridging the skills gap; Identifying security risks
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Applying network redundancy; Overcoming loop tuning challenges; PID control and networks
Driving motor efficiency; Preventing arc flash in mission critical facilities; Integrating alternative power and existing electrical systems
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me