Pipe pressure temperature rating (Pound rating / lb rating)

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Monitor the Situation

Do not leave the pipes unattended. Continue to watch the flow of water until things return to normal, then remove whatever heating device you have on the pipes. If you've been trying for hours and it's not working, it may be time to call in a professional.

Shut Water Off

If you're planning on being gone for an extended period of time, you should shut the main water off and open the faucets. This will decrease the likelihood that you will find frozen or even burst pipes when you return in case of a sudden cold snap. This is something you can do yourself by accessing the home's main water valve.

How to Tell Brass Water Pipes from Copper Piping

Watch outWatch out: on older buildings brass water supply piping may have been used, and may be at or near the end of its useful life

. It can be tricky to tell the difference between brass water supply piping and copper water supply piping if you are not experienced with these materials, as their colors are similar, especially when both types of piping have become an oxidized brownish color with age.

Both brass and copper are non-magnetic, so they won’t respond to a "magnet" test to look for iron or steel.

Brass water supply piping, unlike copper, is a thicker material that is usually joined by threaded fittings of the same size and pipe thread specifications (NPT) as iron and galvanized iron piping.

Usually, brass piping is also so rigid that it is not bendable. Or not very bendable anyway.

So in our photograph (left) of water supply piping at a bath tub in an older home, the larger-diameter left-hand pipe is surely brass, connected to a galvanized iron fitting at its bottom end.

The right-hand vertical pipe may be copper tubing as is the darker copper pipe at left behind our brass one.

Don’t worry about that odd little machine in bottom center of the photo – we were collecting an air sample in this wall cavity.

Flare Fittings Used for Flexible Copper Tubing Connections

Flare fittings used on flexible copper piping and their leaks and defects are discussed



Using a special flaring tool the soft copper tubing or piping is actually spread open or flared at its end in order to mate with the female end of the flare fitting connector shown in our photograph.

Watch out: defects in flare fittings used on flexible copper tubing can result in gas leaks out of gas piping, and in the case of oil piping such as for oil-fired heaters, flare fitting defects result in both oil leaks out of the system and air leaks into the system.

Air leaks into oil piping in turn lead to improper oil burner operation and even potentially dangerous conditions. Flare fitting defects include:

  • Improperly made tubing flares that are too small
  • Improperly made copper tubing flares that are cracked
  • Scratches or gouges on the copper tubing flare or on the brass flare fitting (shown in our photo, above left)

Seat and flare fittings are permitted on K and L copper. LP gas tubing. These fittings are not used on refrigeration equipment.

The Math

The analytical model for copper tube heat loss in circumstances not meeting the above criteria is given as Equations 2 and 3. Equation 2 is the solution to a differential equation describing the heat loss of an infinitesimal length of bare copper tubing of a given size surrounded by air, as shown in Figure 2.

The model was calibrated using the previously mentioned ASHRAE data fit to the function (see Equations 1, 2 and 3.)

Equation 1

Equation 1

In Equation 1:

q’ = heat output of a unit length of tubing (Btu/hr/ft)

Tw = temperature of fluid in pipe (degrees F)

Tair = temperature of air surrounding pipe (degrees F)

a, b = constants determined from a curve fitting procedure

Equation 2

Equation 2

In Equation 2 and Equation 3:

Tout = temperature of fluid leaving the tube (degrees F)

Tin = temperature of the fluid entering the tube (degrees F)

Tair = air temperature surrounding the tube degrees F)

L = length of tube (feet)

f = flow rate (gpm)

Q = heat output of tube (Btu/hr)

c = specific heat of the fluid (Btu/lb/degrees F)*

d = density of the fluid (lb/ft3)*

C1, C2 = constants based on tube size given in Table 1.

* Fluid properties evaluated at the inlet temperature.

Equation 3

Equation 3

Table 1

Copper Tube Size C1 Value C2 Value

3/8″ -0.236326 0.02286

1/2″ -0.238285 0.02665

3/4″ -0.237721 0.03695

1″ -0.236284 0.04595

1.25″ -0.235350 0.05475

1.5″ -0.235693 0.06325

2″ -0.235996 0.07985

2.5″ -0.234942 0.096079

3″ -0.234822 0.11189

Equation 2 tracks the continuous drop in fluid temperature along the tube as heat is dissipated. Equation 3 uses the outlet temperature calculated in Equation 2 to determine the total heat output.

Due to the limited significant figures in the values of C1 and C2, this method should only be used when the length of the tube in feet divided by the flow rate in gallons per minute is OVER 20. When the length/flow ratio is under 20, the total heat loss can be accurately determined using Figure 1.

Equation 2a

Equation 2a

Here’s an example: A 250-foot length of 2-inch bare copper tube operates with water entering at 180 degrees F and 5 gpm. The air around the tubing is at 55 degrees F. Determine the outlet temperature and total heat released from this tube.

The length in feet divided by the flow rate in gpm is 250/5 = 50, thus the analytical model can be used.

The specific heat and density of 180 degrees F water are approximately 1.002 Btu/lb/degree F, and 60.4 lb/ft3, respectively. Substituting this along with the other data into Equation 2, you will find the results achieved in Equation 2a.

Equation 3a

Equation 3a

The total heat output can then be found using Equation 3 (see Equation 3a).

If total heat loss were estimated from Figure 1, the result would be 130 Btu/hr/ft x 250 feet = 32,500 Btu/hr. This is about 5% higher than the result obtained using Equations 2 and 3. Although the difference is small, the analytical model does offer improved accuracy, especially for long piping runs operating at low flow rates.

Manual calculations involving these equations and data are possible, but the overall method begs for software implementation. Equations 2 and 3 and their associated data could be easily integrated into a spreadsheet. The curves in Figure 1 could be described by Equation 1 with the values a and b determined by curve fitting. The software routine could test the length/flow ratio to determine which method to use in finding the overall heat loss.

One thought on “Pressure Temperature Rating and Flange rating of ASME Flanges (With PDF) ”

  1. ZAID ZAID says:

    January 27, 2021 at 12:42 pm

    hi good blog very informative wana know from where 8750 comes in formula as well as need the table for the values s1=133Mpa for c1=10


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Types of Flange Pressure-Temperature ratings

Normally two types of pressure-temperature ratings are used for piping/pipeline flanges. They are

  • Pressure-Temperature rating for API flanges and
  • Pressure-Temperature rating for ASME or ANSI Flanges.

For oil drilling and wellhead system applications API flanges are used which are based on API 6A standard. The pressure-temperature rating for API flanges range from 2000 psi to 20,000 psi.

For all other applications, ASME or ANSI flanges are used which is based on ASME B 16.5 for sizes upto 24″ and ASME B 16.47 for larger sizes.

What is Grade of Copper Nickel Pipe for Heat Exchanger?

When it comes for grades of copper nickel pipes for heat exchanger, you should consider ASTM B111 UNS C70600 or ASTM B111 UNS C71640.