23 Dec

Temperature Considerations for Pressure Relief Valve Application

temperature-considerations-for-pressure-relief-valve-application
The process of selecting or evaluating correct set pressure for pressure relief valve application is relatively straightforward – the set pressure of the pressure relief valve is compared to the pressure vessel maximum allowable working pressure (MAWP). The correct set pressure can be determined by using ASME Code rules and the general principle that at least one valve must be set at or below the MAWP.
The Code does not thoroughly explain temperature considerations, and application concerns related to temperature are just as important as proper selection of the correct set pressure. The purpose of this article is to examine some of these concerns when applying pressure relief valves in pressure vessel service.
One concern is selecting correct material for pressure relief valve construction. For pressure vessels, service temperature is considered part of the vessel design conditions, and the maximum temperature is used to select allowable stress limits for the chosen vessel material. Design temperature is recorded on the pressure vessel’s data report and nameplate (Section VIII, UG-119). Additionally, minimum design metal temperature (MDMT) is also considered in material selection and marked on the nameplate.
Pressure relief valve stamping rules do not require temperature marking on the nameplate; therefore, the valve manufacturer’s literature must be consulted to determine appropriate temperature limits for valve design. The valve must be applied using this data since it represents the mechanical limits of the design. When low temperatures may be encountered, materials appropriate for this application must be selected. Particular attention is called out for application of carbon and low alloy steels when used below -20° F. Impact testing of valve body materials may be required, and alternative materials with better impact resistance characteristics are often selected for low-temperature applications.
Once proper material for a valve is identified, temperature effects on valve operation and capacity must also be considered.
Valves are required to be tested with test fluid similar to the application fluid [UG-136(d)(4)]. Steam valves are tested with saturated steam by the manufacturer; if they are used in saturated steam service, performance inservice should be very similar to how the valve was set.
Valves for gas applications are set using ambient temperature air. Liquid service valves are set using water. The Code makes provisions for use of a cold set pressure which compensates for the difference between test medium temperature during the manufacturer’s original test and the valve’s actual temperature encountered inservice. Temperature of the system fluid, and possibly ambient operating temperature, should both be considered in application of the cold set pressure.
Cold set pressure is typically within several percentage points of the specified valve set pressure. For example, a Dresser 1900 series valve specified for 400° F service will have a multiplier of 1.013 applied to the required set pressure to achieve the desired set pressure inservice. (Reference: Dresser maintenance manual 1900-MM, dated 2009.) For most designs in elevated temperature applications, set pressure on the test stand will be higher than the set pressure inservice. This is because of thermal expansion of the valve’s bonnet (where the spring is located), and relaxation of the spring when it is heated above ambient temperature.
Both final set pressure (set pressure desired inservice), and cold set pressure are listed on the valve nameplate. Cold set pressure is listed as CDTP (Cold Differential Test Pressure). CDTP also includes a differential value to compensate for the effect of back pressure on a conventional type design (no bellows), with the back pressure compensation first considered.
Example using the aforementioned Dresser 1900 series valve:
A valve is required to open at 500 psig inservice where the service temperature is 400° F, and back pressure = 25 psig.
Differential set pressure = 500 psig – 25 psig = 475 psig
Temperature multiplier: 1.013
Cold differential test pressure = 475 psig x 1.013 = 481 psig
This valve would have a stamped set pressure of 500 psig and a CDTP of 481 psig. Back pressure of 25 psig would also be marked. Once the valve is inservice with specified back pressure applied at service temperature of 400° F, it should open at the desired set pressure of 500 psig.
When inservice inspections are performed, stamped set pressure value is compared to the vessel’s MAWP to determine whether set pressure was correctly specified. However, when this valve is tested on a test stand to verify inservice condition, measured set pressure should be compared to the CDTP to evaluate performance.
Interestingly, cold set pressure is usually not specified for valves inservice where temperatures are below ambient. The maintenance manual referenced above did not include a multiplier value for cold temperatures. Another manufacturer of valves for cryogenic services reported it did not use a cold set factor for valves in low temperatures. The reason: the pressure relief valve is normally installed in a location where the valve body is at ambient conditions, and the valves are not normally insulated. Therefore, the valve will operate at a temperature not much different than ambient.
Valves used in superheated steam service will also require a temperature correction, even though tested with saturated steam. Superheated steam is steam with energy added so the temperature is above saturation temperature for the given pressure. Under those conditions, a temperature correction is also applied to test set pressure, based upon the difference between saturated steam temperature and the superheat steam temperature. Manufacturer’s literature should always be consulted to determine the proper use of correction factors.
Valve capacity is also affected by temperature. Valve capacity markings are reported in standard units of pounds per hour of steam, standard cubic feet per minute of air at 60° F, or gallons per minute of water at 70° F. Service fluid temperature may often be different from standard conditions for capacity marked on the nameplate. A conversion from capacity on the valve nameplate to service fluid must be performed to determine whether valve capacity is correctly sized at service temperature conditions.
This calculation can be done using the guidance of ASME Code Section VIII, Appendix 11. Paragraph UG-125(a)(2) of ASME Code Section VIII indicates it is the pressure vessel user’s responsibility to select required pressure relief devices for a pressure vessel prior to initial service. Calculations used to select the pressure relief device should reflect sufficient capacity. When necessary, these calculations must be made available to the inspection organization.
Pressure relief valves are provided for the purpose of plant and personnel safety, and consideration of temperature effects on valve set pressure and capacity are some important aspects to be reviewed during selection and inservice inspection of pressure relief valves for pressure vessel applications.
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29 Nov

Installation Guidelines for a Check Valve

installation-guidelines-for-a-check-valve   Check valves are simple devices that allow fluid media (gas, liquid or solids such as sand or slurry) to flow only one way. Typical check valve installations are found in industrial plants, automobiles, plumbing and ventilation systems. Usually, check valve are relatively inexpensive, compared to more accurate control valves. For a given application, the valve body must be able to contain the media and pressure, and the gate action must have a durable service life. Installing check valves is a matter of determining the correct flow direction for the media and ensuring proper fittings for the inlet and outlet port.

Materials
Installing the correct check valve for a particular process means knowing the media the valve will control. Caustic or abrasive media (lime slurries, acids, cement mixes, etc.) require a check valve resistant to severe corrosion; stainless steel or ceramic check valves work well for such applications. A check valve installed to control hot water flow in a plumbing installation can be made from PVC plastic, brass or steel. As long as the valve can handle the heat and pressure of a standard water line, it will work well.

Installation
Installing a check valve is similar in procedure to installing any other valve with one important distinction: direction. The valve must be installed in the media’s flow direction–nothing can move against a closed check valve gate. Check valve manufacturers include on the valve body an arrow indicating proper flow direction.

Incoming and outgoing lines can be connected using clamps, swage fittings (fittings using a collar around the line, with the fitting and the valve stem hydraulically compressed together) or threaded fittings.

Access
Check valves work automatically to eliminate back flow in a process line. There’s no need for manual operation–the valve can be installed in relatively inaccessible locations. Although other valve installations may require clearance for actuators, access to a manual valve shut off or other features, check valves require little maintenance.

If installed as a diversion valve to relieve excess pressure or heat, the check valve gate can be adjusted to respond to specific pressure settings. For example, a check valve can prevent a steam boiler from building up too much pressure or a car’s radiator from rupturing when the coolant fails: the check valve will divert the high pressure media away from the process and avoid catastrophic failure. When pressure and heat amounts remain within operating limits, the check valve will stay closed.

 

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03 Nov

What is a Plug Valve?

what-is-a-plug-valve

A plug valve is a simple type of valve that allows or blocks the flow of a liquid through a pipe. The plug itself is often shaped like an upside-down ice cream cone or a cylinder. A handle on top allows the user to turn the plug valve so it rotates and stops or starts the flow of liquid. A minimum of two holes, known as ports, must exist in the plug for liquid to flow. The ports are located on opposite sides of the plug, and when the plug is turned to the open position it creates a passage for the liquid to flow through.

This arrangement of two ports is known as a 2-port valve. The pipe in which the plug valve is installed has an area for liquid to flow in and another for liquid to flow out. When the 2-port plug valve is turned on, the ports line up with the holes in the pipe and the liquid flows straight through as if the plug valve was not there. Other, more complex plug valves known as 3-way valves allow liquid to flow to a combination of different ports. One port may connect to either of the opposite two ports, or all three may connect at once.

Two major categories of vales exist: stop valves and check valves. Stop valves follow a basic design structure to turn the flow of liquid on and off, or allow partial flow. Check valves, in contrast, allow liquid to travel only one way and often do not have a handle. Plug valves fall into the stop valve category.

Other stop valve types include gate valves and ball valves. Though similar to plug valves, the shape of the parts and how they work to stop the flow of liquid typically determines the specific group they belong to. Regardless of group, stop valves typically control liquid through the use of a handle.

Operation of a plug valve is simple, making it a common valve choice. The user twists the handle and the ports are moved away from the opening in the pipe. In certain valves, a full turn is not required. Quarter-turn valves, for example, only require the user to make a short, quarter turn to stop the flow of liquid. Often, plug valves can lessen the flow without turning off completely if the user turns the valve half-closed but leaves it open wide enough for some liquid to make it through the ports.

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27 Oct

How Does a Water Check Valve Work?

  how-does-a-water-check-valve-work

    Check Valves

  • Check valves are devices that are installed in pipelines in order to stop the backflow of material. In many cases, the material flowing through the pipe is water, and the check valve keeps the water from flowing backwards in the pipe. They do not require any outside activation, but are rather designed with mechanisms that block the water from reversing direction at a certain point.

     Uses

  • Water check valves are used in several different devices, and they are advantageous for several reasons. For example, they stop flooding or overflowing in sump pumps and water heaters. They protect equipment in control valves, strainers and flowmeters. They also save power, because the backwards-flowing water would use up electricity even when the device was off.

     Types

  • There are several types of check valves that are installed in water-using devices, but they are all based on the same underlying principle. A ball check valve consists of a ball held in place by a spring. When the water flows forward, the spring contracts and the ball is pushed away from the opening of the valve. Therefore, the water can flow through the valve. When the water stops flowing, the spring pushes the ball back into the opening in the valve and stops the water from flowing backwards.Swing valves work in a similar way. Instead of a ball, swing valves contain a small door on hinges. When the water flows by the door, the door swings back on its hinges and allows the water through. When the water stops flowing, the door slams shut and stops any backflow from forming.Similarly, a split-disk check valve contains a metal plate that folds in half as the water flows past it. When the water stops flowing, the plate springs open and blocks the entrance of the valve.

 

 

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17 Oct

Instrumentation Valves And Fittings Market to Reach $5.63 billion with 5.5% CAGR

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  According to researcher, the Global Instrumentation Valves and Fittings market is expected to grow from $3.86
billion in 2015 to reach $5.63 billion by 2022 with a CAGR of 5.5%. Huge requirement for valves and fittings in in
dustrial automation in fumes, fluid, and gas control applications is the major factor driving the market growth. In
addition, growth in usage of instrumentation valves on account of increasing growth rate of hyperbaric oxygen
therapy devices is also favouring the market growth.

Ultraclean valves market is anticipated to grow at a higher CAGR during the forecast period. It is attributed to exte
nsive usage in pharmaceutical sector for ultra-hygienic applications. The oil & gas application is leading the glob
al market. It is led by increasing market demand for valves in the instrumentation valves & fittings market. North
America and Europe are projected to be the leading markets in terms of market size, during the forecast period. A
sia Pacific and Latin America are expected to witness high growth rate during the forecast period.
Some of the key players in global instrumentation valves and fittings market include Fujikin., Dwyer Instruments,
Fitok, Bray International Inc., Braeco., Hoke., Hex Valve, Ham-Let, Astectubelok, As-Schneider, Hy-Lok, Ssp Fitt
ing, Oliver Valves, Safelok, Swagelok, and Parker Hannifin.

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09 Sep

Ball Valves Segment Will Continue to Dominate the Global Valves and Manifolds Market Until 2020, Predicts Technavio

ball valvesAccording to the latest market study released by Technavio, the global valves and manifolds market is expected to grow at a CAGR of 6.56% during the forecast period.

This research report titled ‘Global Valves and Manifolds Market 2016-2020’ provides an in-depth analysis of the market in terms of revenue and emerging market trends. This market research report also includes up to date analysis and forecasts for various market segments and all geographical region

Based on product, the report categorizes the global valves and manifolds market into the following segments: ball valves, needle valves, check and relief valves, manifolds, and others. The top three revenue contributors are illustrated below:

Global ball valves market

Technavio predicts the global ball valves market to reach USD 432.9 million by 2020, an increase from USD 320.8 million in 2015.

Ball valves are capable of withstanding corrosive substances flowing through them. Operating temperatures range from as low as -328°F to 932°F. These valves can endure the high pressure of compressor stations that are used to keep the movement of natural gas smooth through pipelines. Ball valves find extensive application in the oil and gas industry, specifically for FPSO, pipelines, offshore production platforms, gas storage applications, tank farms, specialized LNG applications, and emergency shut down situations.

According to Anju Ajaykumar, a lead analyst at Technavio for research on tools and components, “Increase in the construction of new industrial plants, especially in the oil and gas and process industries, and the capacity expansion of existing plants have led to a growing demand for ball valves. Industries worldwide are upgrading their existing plants to increase production efficiency and reduce labor costs, which has led to the increased installation of such valves. Also, the availability of new and innovative quarter-turn valves has enabled end-users to carry out production more efficiently.”

Global needle valves market

Technavio predicts the global needle valves market to grow at a CAGR of 6.31% to reach USD 288.4 million by 2020.

The global needle valves market is seeing increased demand from the food and beverages and pharmaceutical industries. In these industries, needle valves are used for filtration purposes. The development of new products and the constant upgrading of existing lines will create demand for needle valves in these industries. “The presence of several food and beverages and pharmaceutical industries in APAC has contributed to the growth of the market in the region. APAC has the largest number of consumers of multi-turn valves,” adds Anju.

Global check and relief valves market

The global check and relief valves market was worth USD 221.3 million in 2015. Technavio predicts the market to reach USD 312.1 million by 2020.

The major end-users of check and relief valves are oil and gas production, petrochemicals, steel/primary metals, pulp and paper, marine, and food processing industries. Check and relief valves offer leak-free and secure connections and incur low cost. The increased adoption of these valves in many other end-user applications will drive the market. For instance, these valves are used extensively in medical facilities; they have their own special requirements such as reliability, safety, cleanliness, quiet operation, and need to replace components quickly is especially critical for life support systems. The valves that are used in medical facilities are medical gas ball valves, medical gas check valves, and vacuum and pressure relief valves for vacuum.

The top vendors highlighted by Technavio’s research analysts in this report are:

  • Circor Instrumentation
  • DK-Lok
  • Ham-let
  • SSP
  • Swagelok

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