Question of the Month: 2014

Question of the Month for December 2014

QUESTION:

In order for a reciprocating pump to be used as a feed water pump, the steam piston must be how many times larger in diameter than the water piston?

ANSWER:

The steam piston must be 2 times to 2 1/2 times larger in diameter than the water piston.  This design allows sufficient pressure to develop on the water side , which will overcome boiler pressure

while using the steam pressure from the boiler to operate the pump.

Recip Fd Pmp

Question of the Month for November 2014

QUESTION:

The pressure at the base of a vertical foot of water is _____psi

A. 0.433

B.8.3

C. 14.7

D. 34.5

ANSWER:

A: 0.433

Since water is essentially a non-compressible liquid it exhibits the unique trait of transferring pressure horizontally when in a confined space. What this means is that water in a pipe (which is a confined space) exhibits the same pressure as it would if the pipe were perfectly vertical, even if the pipe isn’t. This isn’t an easy principle to understand, so be patient and re-read as needed. The best way to demonstrate this is with a picture.

sprinkler11aIn this picture the water pressure in the water tank at the top of the water surface level is 0 feet of head, or you could also say there is 0 PSI. This is because there is no water above it to create pressure. Head is another word that indicates pressure, it is mostly used when measuring pressure created by the depth of water. So 10 feet deep water will create 10 feet of head at the 10′ deep level. So 10 feet of depth = 10 feet of head. Ok? (Yes, I know there would be a small amount of additional water pressure due to the air pressure above the water, but let’s try not to confuse things. This is hard enough to understand! So we’re going to say that there is 0 feet of head at the water surface.)

Looking again at the picture above, we see that the ground level is 40 feet below the water level in the tank. Therefore the water pressure at ground level is 40 feet of head. Again 40 feet of depth = 40 feet of head. Now lets convert that to pressure measured in PSI. As noted earlier, 1 foot of elevation change creates 0.433 PSI of water pressure. So in this case 40 feet of head is going to be about 17 PSI. (40 ft head x 0.433 psi/ft = 17.3 PSI.) Again, the formula is “feet of head x 0.433 = PSI.” So far, pretty straight forward. Read again if you’re confused.

Static Water Pressure

Now the hard to understand part. In the drawing above, the water enters the house at a level 100 feet below the water level in the tank. So the static water pressure at the house is 100 feet of head, or about 43.3 PSI, using the formulas in the previous paragraph. Note that I said this is the “static pressure”. So now you’re likely wondering how this could be? The water level is not just 100 feet above the house there is also easily 180 feet of pipe between the tank and the house! The answer is that the length of a pipe does not matter when the water is static in the pipes. Static means the water is not flowing, it is not moving, it is standing still. This is very important! Because the water is a non-compressible liquid it transfers the pressure horizontally along the pipe route for pretty much any distance without any loss of pressure! Cool, right? You bet it is, it is a principle that is very handy and makes all sorts of neat gadgets used on machines work. This is why a small hose filled with hydraulic fluid can cause the brakes on every wheel of a mile long train to apply when the engineer hits the brakes!

Now on the other hand, if we measured the pressure with the water flowing, then the pressure would be termed “dynamic pressure”. With the water in a dynamic state (flowing in the pipe) the water would loose pressure due to friction on the sides of the pipe and we would get a lower pressure reading at the house shown in our previous diagram. (I’ll deal with dynamic pressure in the next paragraph.) So for now, just understand that static pressure means there is no flow in the system, so there is no friction, and no pressure loss! Read that last sentence again! Think about it for a second, go back look at the picture again if you need to. It makes sense if you think about it. Our professor spent a week drilling this concept into us back in college and a lot of people in the class never did understand it! So if you still don’t get it don’t feel bad and don’t get discouraged! Just accept it on faith (I wouldn’t lie to you) and continue on.

In most cases we use static water pressure values when designing irrigation systems (or any other water piping system for that matter.) Then we can use calculators, spreadsheets, or charts (if you really want to torture yourself you can even use a very complicated manual calculation) to estimate the “friction loss” that will occur in the pipes when the sprinkler system is operating. Then we will subtract the friction loss from the static pressure to arrive at the dynamic pressure. Why not just turn the water on and measure the dynamic pressure with the water flowing? It would seem simpler, then we would not have to prepare a separate calculation for friction loss, right? Well, that is correct, however dynamic pressure is extremely difficult to measure accurately! You have to get the flow just right, and then hold the flow at that level for a minute or two while the pressure stabilizes. This is a real pain in the rear to do and not nearly as easy as it sounds! Plus, it is a bit hard to do if the pipe isn’t installed yet! You can’t measure the dynamic pressure if the pipe isn’t installed! So, the result is that we almost always will work by using static water pressure and then use calculations to determine the dynamic pressure. Its just way easier to do, and who wants to do it the hard way?

Now go back and look at that picture at the top of the tank and house again. As the water flows to the house the water level in the tank will go down (assuming water isn’t flowing into the tank to refill it.) So the elevation of the top of the water in the tank will drop as the tank empties. When the tank is almost empty the difference might be only 95 feet. So since the water depth is less, the water pressure would also be lower. This happens all the time and is normal! If the top of the water elevation varies, then the water pressure will also vary. So if the water level will vary at your water source, the pressure will also vary. I know I keep saying the same things over and over in different ways, but I’m trying to drive home some important, but hard to understand, principles! My apologies if you got it the first time through and are getting bored!

Question of the Month for August 2014

QUESTION:

The term stoker implies?

ANSWER:

The term stoker implies a boiler that automatically feeds (or ” stokes”) the boiler.

 Stoker coal size is typically 1.25 inches maximum with less than 30% under 0.25 inches.

 Question of the Month for July 2014

QUESTION:

Boiler plates and staybolts are subjected to ____ stress?

a. Tensile

b. Compressive

c. Shear

d. None when under pressure

ANSWER:

a, Tensile

Question of the Month for June 2014

QUESTION:

A firetube boiler may be used _____?

a.  only in low pressure plants

b.  only in high pressure plants

c.  in both high or low pressure plants

d.  only for process steam

ANSWER:

Question of the Month for April 2014

QUESTION:

A firetube boiler may be used _____?

a.  only in low pressure plants

b.  only in high pressure plants

c.  in both high or low pressure plants

d.  only for process steam

ANSWER:

c.  in both high or low pressure plants

Description and Overview Firetube boilers may be used in steam or hot water applications within the scope and service restrictions of ASME Section I and Section IV. They may also be used to heat or vaporize liquids other than water, such as an organic or synthetic fluid.

Firetube boilers can be constructed in different configurations. The most common designs are:

  • Horizontal Return Tubular (HRT) – this is an old and very simple design which is still being manufactured. The boiler consists of a shell, a tube sheet on each end of the shell, and tubes connecting the two tube sheets. The boiler is mounted above a steel or masonry furnace. The products of combustion leave the furnace and are directed through the tubes at one end of the boiler. After passing through the tubes, the products of combustion exit the opposite end of the boiler and are directed to the stack or chimney.
  • Firebox – this type of boiler includes locomotive boilers as well as what some have called firetube firebox boilers. The products of combustion pass through a locomotive boiler one time giving it a general classification of a one-pass boiler. Some firetube firebox boilers may be two-pass or three-pass depending upon the arrangement of baffles and tubes. The common characteristic of firebox boilers is that the furnace is at least partially contained within the boiler and is water cooled for a large portion of its surface area. Multi-pass firebox boilers are very common and many older examples will be found in places such as schools where they are used to heat water or produce steam for space heating applications.
  • Scotch – this type of boiler is commonly referred to as a scotch marine boiler. In a scotch boiler, the furnace is a large diameter tube, within the boiler, surrounded by water. Some older, large scotch boilers had two or three furnaces but modern boilers typically have only one. Scotch boilers may be two-pass, three-pass, or four-pass depending upon the arrangement of baffles and tubes. Four passes are generally recognized as the practical maximum when balancing economic heat transfer and condensation induced corrosion. Each pass through the boiler transfers heat from the products of combustion to the water in the boiler. After a number of passes, it becomes more difficult to economically extract heat from the cooling products of combustion. Additionally, if the products of combustion are cooled too much, the combustion gases will condense which can cause corrosion. A further subclassification of scotch boilers describes the end closure opposite the burner end of the boiler. A wet-back means the end closure is water cooled and a dry-back means the end closure is not water cooled and relies on fire brick, refractory, or a combination of both to prevent the end closure from overheating.
  • Vertical – this type of boiler is a one-pass boiler with the furnace at the bottom and tubes running between the lower and upper tube sheets. The furnace can be enclosed on its sides with a water cooled jacket or it may be made up of masonry. The top tube sheet in a steam boiler can be above or below the water line. When it is above, it is called a dry-top and when it is below, it is called a wet-top. A vertical boiler has a small “footprint” and can be installed in boiler rooms with limited space. Vertical boilers are very popular in the dry cleaning industry.

Appurtenances, Settings, and Piping Section IV steam boilers must have at least one safety valve with a set pressure not to exceed 15 psi. The safety valve inlet must not be smaller than NPS ½ nor larger than NPS 4 ½ . Section IV hot water boilers must have at least one safety relief valve with a set pressure at or below the maximum allowable working pressure (MAWP) marked on the boiler. The safety relief valve inlet must not be smaller than NPS ¾ nor larger than NPS 4 ½ . The minimum relieving capacity of safety or safety relief valves on Section IV boilers must equal or exceed the maximum output of the boiler. More information on Section IV safety or safety relief valve requirements can be found in ASME Section IV, HG-400 and HG-701.
Section I boilers must have at least one safety or safety relief valve. If the boiler has more than 500 square feet of bare tube water heating surface, then it must have two or more safety or safety relief valves. One or more safety valves on a Section I steam boiler must have a set pressure at or below the MAWP of the boiler. If more than one valve is used, the highest set pressure cannot exceed MAWP by more than 3%. Additionally, the complete range of safety valve settings cannot exceed 10% of the highest set pressure. Safety relief valve settings on high temperature water boilers are permitted to exceed the 10% range referenced above. The minimum required relieving capacity of the safety or safety relief valves must not be less than the maximum designed output at the MAWP of the boiler as specified by the boiler manufacturer. Details concerning minimum required relieving capacities for organic fluid vaporizers can be found in ASME Section I, PVG-12. More information on Section I safety or safety relief valve requirements can be found in ASME Section I, PG-67 and PG-71.
Safety or safety relief valves must be installed so the spindle is in a vertical position.

Each steam boiler must have:

  • A pressure gage with an internal siphon, a siphon in the gage piping, or equivalent protection (PG-60.6, HG-602).
  • A water level indicator (PG-60.1, HG-603).

Each Section IV steam boiler must have:

  • Two pressure controls (if the boiler is automatically fired); one is considered the operating control and the other is considered the high-limit control (Note: some jurisdictions require the high-limit control be equipped with a manual reset switch) (HG-605).
  • An automatic low-water fuel cutoff – if the boiler is automatically fired (Note: some jurisdictions require an additional low-water fuel cutoff with a manual reset switch) (HG-606).

Although not referenced in Section I, there should be some means of controlling pressure. This will vary with the size and complexity of the boiler.

Each Section I steam boiler with more than 500 square feet of water heating surface must have at least two feedwater methods. If solid fuel, not in suspension, is used to fire the boiler or, if the furnace design can provide enough heat to damage the boiler after the fuel supply is stopped, the two feedwater methods must be independent so as to prevent one method from being affected by the same interruption as the other method (PG-61). Using this type of fuel or furnace design does not lend itself well to relying upon a low-water fuel cutoff. This is the reason for requiring two means of supplying feedwater.

If solid fuel in suspension, liquid or gaseous fuel, or heat from a turbine engine exhaust is used to fire a Section I steam boiler, one source of feedwater supply is acceptable if the heat input can be shut off before the water level reaches its lowest permitted level. This scenario does work well with a low-water fuel cutoff. The inspector should not panic if the typical float-chamber type low-water fuel cutoff is not found on a large Section I boiler. The same results can be achieved with other styles of mechanisms or controls. It is better to simply ask the owner or owner’s representative how the boiler is protected from low-water conditions and then tailor that part of the inspection around the method in use.

Each Section I high-temperature water boiler must have:

  • A pressure gage (PG-60.6).
  • A temperature gage (PG-60.6.4).
  • Although not referenced in Section I, there should be some means of controlling temperature. This will vary with the size and complexity of the boiler.
  • A means of adding water to the boiler while under pressure (PG-61.4). (There is no reference to a low-water fuel cutoff in Section I, but some installations may use such a device.)

Each Section IV hot water boiler must have:

  • A pressure or altitude gage (HG-611).
  • A thermometer (HG-612).
  • Two temperature controls (if the boiler is automatically fired); one is considered the operating control and the other is considered the high-limit control (Note: some jurisdictions require the high-limit control be equipped with a manual reset switch.) (HG-613).
  • An automatic low-water fuel cutoff – if the boiler is automatically fired and has a heat input greater than 400,000 Btu/hr. (Note: some jurisdictions require an additional low-water fuel cutoff with a manual reset switch. )(HG-614).
  • Provisions for thermal expansion (HG-709).

Clearances on the front, rear, sides, and top of all firetube boilers for operation, maintenance, and inspection shall meet jurisdictional requirements. If no jurisdictional requirements exist, then the boiler manufacturer’s requirements shall be met.

All firetube boilers should be installed on foundations or supports suitable for the design and weight of the boiler and its contents. The foundation or support must also be unaffected by the heat of the operating boiler.

Section I boiler external piping is covered by PG-58 which references ASME B31.1.

Some jurisdictions may also regulate the piping which lies beyond the limits imposed by Section I.

Although most jurisdictions do not require inspection of the piping associated with a Section IV boiler, there are some installation requirements in Section IV the inspector should review. Please see HG-703 and HG-705.

Common Observations and Problems Firetube boilers can come in different sizes and configurations; therefore, it is difficult to list a common set of problems.

Water leaks are always a possibility, especially with older boilers where corrosion may have been occurring for several years. The firetubes will be the thinnest material in the entire boiler and if corrosion (either fireside or waterside)is very aggressive, they will show signs of leakage. This is easily detected if the inspector sees water in the furnace or any other fireside space.

Mud legs in locomotive or other firebox type boilers suffer from poor water circulation and many times will exhibit the most waterside corrosion compared to the rest of the boiler. The welded or threaded stays within the mud leg can also be thinned, sometimes to the point of separation.

Scotch boilers sometimes have poor water circulation between the bottom of the furnace tube and the bottom of the boiler shell. In addition, it may be worse at different locations along the length of the furnace tube. When inspecting this area, the inspector should look for accumulations of sludge or sediment within the entire length of the boiler shell. If one area is clean, it must never be assumed the other areas will be clean. The top of the furnace tube (waterside) can also be a location for sludge or sediment to collect. Any sludge or sediment build-up which rests against the furnace tube can adversely affect its ability to transfer heat to the surrounding water. This can cause the furnace to overheat and, in some cases, the furnace will collapse.

If there is poor or no water treatment, sediment can accumulate enough to plug the spaces between the tubes in extreme cases. Just as with the furnace, this condition can lead to overheated and damaged tubes.

The fireside of the tubes can also be subject to scale and deposit build-up when the boiler is fired with oil or solid fuel. This adversely affects boiler efficiency and can cause the tubes to overheat.

Tube ends that are projecting beyond the tube sheet more than the Code allows can overheat and crack. If the tubes are attached to the tube sheet by welding, cracks in the tube ends can propagate to the tube sheet, and possibly run into the ligaments between the tubes. A tube sheet can easily be damaged beyond repair with cracks of this nature, and it can start with a fraction of an inch in excess tube projection. Please see PFT-12.2, HG-360.2, and HW-713.

External – while in operation

Upon entering the boiler room, the inspector should perform a general assessment of the boiler, piping, controls, fuel system, and combustion air supply.

The inspector should then:

  • Review the current operating certificate (if one was issued in the past) and compare the information to the associated boiler and its stamping or nameplate.
  • Compare the safety or safety relief valve(s) nameplate data (set pressure and relieving capacity) with the boiler stamping or nameplate to ensure the safety or safety relief valve(s) is(are) adequate for this installation.
  • Inspect the safety or safety relief valve operation as described in the National Board Inspector Guide for Pressure Relief Devices.
  • Inspect the low-water fuel cutoff and water feeding device (if applicable) as described in the National Board Inspector Guide for Water Level Controls and Devices.
  • Inspect the feedwater supply system (if applicable) to ensure it meets Code and jurisdictional requirements.
  • Inspect the pressure or temperature controls as described in the National Board Inspector Guide for Operating Controls.
  • Check the pressure or altitude gage reading (if there is a reason to question the accuracy of the gage, it should be replaced or recalibrated).
  • Check the temperature gage reading on Section I high-temperature water boilers, or the thermometer reading on Section IV hot water boilers. (If there is a reason to question the accuracy of either, they should be replaced or recalibrated.)
  • Check the water gage glass to ensure it provides a clear indication of the water level in a steam boiler. (Please see the National Board Inspector Guide for Water Level Controls and Devices.)
  • If a steam boiler has a MAWP over 400 psi, ensure that any remote water level indicators are functioning and indicate the same water level as the gage glass (PG-60.1.1).
  • Look closely for leaks at all pipe connections associated with the boiler.
  • Look closely for leaks originating from under the boiler casing and insulation and instruct the owner or owner’s representative to remove the casing and insulation as necessary to pinpoint any leaks.
  • Look for evidence of overheating.
  • Witness any pressure test required by the jurisdiction.
  • Inspect the fuel-burning apparatus as required by the jurisdiction.

Internal

Internal inspections of firetube boilers can range from looking into inspection openings with a mirror and flashlight to actually crawling inside when the boiler and access openings are large enough. Any time the inspector’s head enters the fireside or waterside of the boiler, the atmosphere must first be checked for oxygen content and the presence of flammable, explosive, or hazardous gases. The inspector must comply with all applicable confined space entry rules and procedures.

The inspector should:

  • Look in all inspection openings to check for scale, sludge, and sediment and, instruct the owner or owner’s representative to remove any build-up which prevents a thorough inspection.
  • Look for corrosion, overheating, bulges or blisters, and cracks.
  • Look at the steam/water line area for evidence of corrosion and oxygen pitting on steam boilers.
  • Investigate any appearance of water in the fireside spaces.
  • Check all stays with telltale holes for evidence of leakage through the hole which would indicate a broken stay.
  • All stays should be examined to determine if they are sound and able to support the stayed area.
  • Check for cracks in the tube ends and tube sheet ligaments.
  • Look through the tubes to check for obstructions and sagging of the tubes.
  • Ensure that refractory and/or fire brick is properly placed and secure.
  • Look for flame impingement on any surfaces exposed to the direct flame.
  • Ensure any supporting structure or foundation for the boiler is in good condition.
  • Examine the interior and operating mechanism of float-type low-water fuel cutoffs and water-feeding devices.
  • Ensure that all piping and connections for low-water cutoffs, water columns, and gage glasses are free of obstructions.

Miscellaneous Information Additional information to aid inspections of firetube boilers can be found in the following publications and sources:

  • National Board Inspection Code
  • ASME Section I
  • ASME Section IV
  • ASME Section VI
  • ASME Section VII
  • ASME CSD-1
  • NFPA 85
  • Manufacturer’s Installation, Operation, and Maintenance Documentation
  • Jurisdictional Laws, Rules, and Directives

Question of the Month for April 2014

PROBLEM:

A coal has an ultimate analysis of  78% carbon, 4% hydrogen, 3% oxygen, 6% sulfur, and 9% ash.

Estimate the HHV of the coal.

SOLUTION:

Use the Dulong formula:

HHV 14,600 X 0.78 + 62,000 X (0.04 – 0.03/8) + 4050 X 0.06

HHV 13,900 Btu/lbm

Question of the Month for March 2014

According to the ASME Code, when no boiler water analysis is made the boiler should be blown down at least once ______?

                                                                                                                                                                    a.    every 8 hours

                                                                                                                                                                    b.    every 24 hours

                                                                                                                                                                    c.   a month

                                                                                                                                                                    d.  a week

Answer:     b.  every 24 hours

There are three main factors that affect the Boiler Blowdown rate. These factors are steam consumption, concentration of impurities in the feed water and maximum allowable TDS in the boiler.

The blow down is the water removed from boiler to maintain the solids level in the boiler drum. This can be calculated as follows:

E = Evaporation or steam generation rate.

S = Amount of solids (ppm)

B = Blow down (m3 / hr)

C = Maximum permissible concentration of solid inside the boiler drum

Blowdown

The American Society of Mechanical Engineers (ASME) has developed a best operating practices manual for boiler blowdown. The recommended practices are described in Sections VI and VII of the ASME

Boiler and Pressure Vessel Code. You can identify energy-saving opportunities by comparing your blowdown and makeup water treatment practices with the ASME practices. The ASME Boiler and Pressure Vessel Code can be ordered through the ASME Web site at http://www.asme.org/bpvc/.

Question of the Month for February 2014

A Ringelmann test is used to?

  a.  analyze feedwater

              b.  measure CO2 in flue gas

            c.  measure CO in flue gas

                 d.  determine smoke density

Answer:     d.  determine smoke density 

The Ringelmann Smoke Chart, giving shades of gray by which the density of columns of smoke rising from stacks may be compared, was developed by Professor Maximilian Ringelmann of Paris. Ringelmann, born in 1861, was professor of agricultural engineering at l’Institute National Agronomique and Director de la Station d’Essais de Machines in Paris in 1888, and held those positions for many years thereafter. The chart apparently was introduced into the United States by William Kent in an article published in Engineering News of November 11, 1897, with a comment that he had learned of it in a private communication from a Bryan Donkin of London. It was said to have come into somewhat extensive use in Europe by that time. Kent proposed in 1899 that it be accepted as the standard measure of smoke density in the standard code for power-plant testing that was being formulated by the American Society of Mechanical Engineers. The Ringelmann Chart was used by the engineers of the Technologic Branch of the U.S. Geological Survey (which later formed the nucleus of the present Bureau of Mines) in their studies of smokeless combustion beginning at St. Louis in 1904, and by 1910, it had been recognized officially in the smoke ordinance for Boston passed by the Massachusetts Legislature.

The chart is now used as a device for determining whether emissions of smoke are within limits or standards of permissibility (statutes and ordinances) established and expressed with reference to the chart. It is widely used by law-enforcement or compliance officers in jurisdictions that have adopted standards based upon the chart.

The Ringelmann system is virtually a scheme whereby graduated shades of gray, varying by five equal steps between white and black, may be accurately reproduced by means of a rectangular grill of black lines of definite width and spacing on a white background. The rule given by Professor Ringelmann by which the charts may be reproduced is as follows:

Card 0—All white.

Card 1—Black lines 1 mm thick, 10 mm apart, leaving white spaces 9 mm square.

Card 2—Lines 2.3 mm thick, spaces 7.7 mm square.

Card 3—Lines 3.7 mm thick, spaces 6.3 mm square.

Card 4—Lines 5.5 mm thick, spaces 4.5 mm square.

Card 5—All black.

Question of the Month for January 2014

To start a turbine pump, the discharge valve should be?

  a.  Closed

b.  Open

                                     c.  There is no dicharge Valve

   d.  Primed

Answer:     B. Opened

A turbine pump is a  centrifugal pump that is mainly used to pump water from deep wells or other underground and man-made bodes of water to water distrribution systems. A centrifugal pump consists of a pump shaft, a rotating device known as an impeller, and a motor or an engine. A turbine pump may consist of multiple semi-open or enclosed impellers, also known as “stages.” A metal plate called shroud supports the vanes of the impeller in an open or semi-open impeller, whereas in an enclosed impeller, the shroud encloses the impeller vanes. The pump also has a water intake point and a water discharge point.

The motor on this type of pump is usually placed above the water level, but submersible types are available depending on the requirement of the application. The total energy taken by the pump to move water from the resource — i.e., the supply tank — to the point of discharge is known as total head. The total head of a powerful pump can exceed several hundred feet (over 70 meters).

turbine pump 1