Steam Piping Best Practices | (2024)

Steam Piping Best Practices | (1)Introduction

Just because it’s ‘been that way’ for a long time, don’t assume it’s right. In many cases steam systems were designed long before there was any concern about energy efficiency. Systems may have not been installed according to design because of some problem in the field – either something didn’t fit, got changed or an installer thought they had a better idea. Systems are often modified over the years; equipment, pipes and valves are moved so that they no longer perform in the way they were originally intended. All of these factors and more are reasons to expect that steam piping systems could be improved when the objective is better function and energy efficiency.

Problems with steam systems are not always obvious as equipment may continue to function, although impaired. Some problems lead to premature failure of equipment, but it may not be obvious what the cause of the failure was.

If a facility has not had a thorough review of its steam distribution system by a competent expert, then there are likely many things that an audit would reveal. The following examples are common problems discovered in the course of steam system audits by Duane Hagen of Merlo Steam (see links below). These are real facilities that in many cases were in improper operation for a number of years prior to the audit.

Problems and Fixes

Steam Piping Best Practices | (2)Steam Trap Installed Wrong

It is clear from the picture that this trap has been here a long time. What is not so obvious to the untrained eye, is that this trap is installed wrong.

Steam Piping Best Practices | (3)

This trap is a ‘Float and Thermostatic type. It must be installed so that the bolted-on flat plate is in a vertical position. When it is horizontal as in this installation, the float is not a float but a pendulum (See the sectional illustration to the right).

When steam traps are improperly installed, they cannot function properly and therefore either do not remove the condensate, let steam blow through, or both.

Steam Piping Best Practices | (4)Other Components Installed Wrong

It is common to find many types of steam system components installed incorrectly. In this example, a mechanical check valve that requires gravity to operate properly is installed upside down. It is impossible for this check valve to function when installed this way.

However, it is probably a good thing that it is upside down, as it is also installed backwards. If it were installed upright, it would block flow in the wrong direction.

Steam Piping Best Practices | (5)Failed Valves

This valve is obviously stuck partly open. However, often valves are installed with pipe on the down-stream side. As in the picture, steam still blows past the valve, but since its inside of pipe, it’s not obvious.

Valves fail due to wear, corrosion and dirt/contaminates stuck in the valve seat.

Steam Piping Best Practices | (6)High and Low Pressure Systems Interconnected

In facilities with high and low steam operating pressure systems, all steam and condensate lines should be properly identified and checked. Be sure that high and low pressure systems are not interconnected at any location, even on condensate systems.

High pressure condensate can flash to steam in low pressure condensate systems causing problems with their operation and wasting steam. Use aflash steam recovery system to flash high pressure condensate to steam and then inject the steam into the low pressure steam system.

Steam Piping Best Practices | (7)Supply Lines and Condensate

Long steam supply lines should be trapped to remove condensate and keep the steam dry. In the photo to the right, there is a steam trap off the steam main, and condensate is returned to the to the top of the condensate pipe. However, the steam trap is piped off the TOP of the Steam Main. Because condensate is on the bottom of the pipe, this trap is doing nothing to help keep the line dry.

Worse, not only is it not removing condensate, it is actually wasting energy. Steam comes off the top of the Steam Main, comes down to the trap along the vertical pipe in the left of the photo, as it is cooled by heat loss from the pipe. This steam trap is therefore acting mostly as a “steam cooler” wasting steam from the Steam Main.

Note the nice insulation job however; this is probably keeping the problem from being much worse.

Condensate should always be drained from the BOTTOM of the steam line in low sections of pipe and at changes in direction, such as a 90 Degree turn. Condensate from steam traps should always be returned to the TOP of condensate lines; the maximum height of rise above the steam trap to the condensate line is a function of steam pressure and the type of trap. A general rule of thumb is that 1 psi of steam will raise water about 2 feet. For example, a 5 psi system should not have condensate lines higher than 10 feet above the steam trap.

Steam Piping Best Practices | (8)Properly Size Steam Trap Drip Leg Lines

Not only must steam traps be piped off the bottom of the steam lines, the pipe must be properly sized. If the condensate drip legs are too small, the condensate will simply blow past the drain line.

Condensate drip legs should be sized according to the line they are draining. See the Chart for suggested sizes.

Steam Piping Best Practices | (9)

Steam Piping Best Practices | (10)

Source: Armstrong International

See also Condensate Return

Steam Piping Best Practices | (11)Control Systems

In order for steam system controls to function properly, they must be installed properly.

In the photo to the right, a green-headed PRV (Pressure Reducing Valve) has been installed to reduce the higher pressure steam from the main steam header, to a lower pressure for use in a low pressure application – such as space heating.

This type of PRV requires a down-stream sensor line to monitor the pressure and supply a check pressure back to the PRV.

The problem is that the control line is installed vertically higher than the PRV, resulting in the line going downhill back to the PRV. There is no place for the condensate to drain through the PRV, so it will fill/flood with condensate. When this happens, the PRV cannot accurately control the low pressure and premature failure of the PRV will likely result as it constantly chatters attempting to control the pressure.

Steam Piping Best Practices | (12)

The correct way to install a PRV is shown in the above diagram. There must be a minimum distance between the PRV and sensing point, and the control line must slope down to the pipe – NOT the PRV, so that condensate will drain back to the steam line where it will be removed by a steam trap.

NOTE: There are also internally monitored PRV valves that do NOT require an external sensing / control line. Therefore, do not be alarmed if the PRV has no sensing line; but if it has a line, be sure that it is installed correctly.

Steam Piping Best Practices | (13)Water Hammer

Water hammer is the result of condensate not being removed from long runs of steam lines. Steam moving through a line at high speeds picks up condensate in the bottom of the pipes, much like wind blowing across a lake forms waves. When the high speed steam and condensate come to a bend, such as a ‘Tee’ or 90 Degree turn, the steam makes the transition, but the water slams into the side wall of the pipe. A pulsing action results in a hammer-like action called ‘water hammer’. Water Hammer can destroy controls, insulation, pipe, break fittings, and cause a lot of undesirable noise.

This photo shows evidence of water hammer at a ‘Tee’. Note that the insulation is gapping from the pipe – evidence that the pipe has been moving against the insulation, compressing it. The grey patches show an attempt to repair the insulation. There probably needs to be a steam trap installed on this line, or if there is a steam trap, it may not be working correctly.

Steam Piping Best Practices | (14)“Missing” Steam Traps

On the other side of this wall there is a long run of steam pipe; it then makes 2 sharp 90 Degree bends. The second bend, the lower one in the photo, would be a good spot for steam trap to drain condensate from the line.

Steam Piping Best Practices | (15)Leaking Equipment

Leaking steam coils, especially in equipment less than 30 years old, can be an indicator of improper seasonal shut-down, steam trap problems, or water hammer damage.

A closer inspection of this unit heater revealed that there was no way for the condensate to be drained out at the end of the heating season. Stagnate condensate can form a mild carbonic acid when CO2 comes in contact with water. This accelerates corrosion faster than water alone.

Steam systems should be piped to allow gravity drain-down when not in use, or should be blown out with compressed air at the end of each heating season.

Source: Thanks to Duane Hagen of Merlo Steam for providing these photos and an explanation of what the problem is and the best way to fix it. Duane and Merlo Steam conduct customized in-house training on steam system operation and perform steam distribution system audits. For information about an audit or training program, contact Duane at Steam Piping Best Practices | (16)269-833-7129, or see their web site

Merlo Steam
35745 Beattie Drive
Sterling Heights, MI 48312

Telephone: Steam Piping Best Practices | (17)1-800-969-9779 FREE

Steam Piping Best Practices | (2024)


Steam Piping Best Practices | ›

A general rule of thumb is that 1 psi of steam will raise water about 2 feet. For example, a 5 psi system should not have condensate lines higher than 10 feet above the steam trap. Not only must steam traps be piped off the bottom of the steam lines, the pipe must be properly sized.

What is the proper steam boiler piping? ›

Proper near-boiler piping ensures that dry steam is delivered to the system, reduces water hammer and increases overall system efficiency. Steam piping should be pitched at a rate of a quarter to half inch for every 10 feet away from the boiler. Any angle less than this may allow condensate to pool inside of piping.

Should steam pipe be schedule 40 or 80? ›

There are eleven Schedules ranging from the lowest at 5 through 10, 20, 30, 40, 60, 80, 100, 120, 140 to schedule No. 160. For nominal size piping 150 mm and smaller, Schedule 40 (sometimes called 'standard weight') is the lightest that would be specified for steam applications.

What is the recommended slope for steam piping? ›

Good practice is to size the pipe on a low steam velocity of not more than 15 m/s, to run the line at a slope of no less than 1:40, and install the drain points at not more than 15 metre intervals (see Figure 10.3. 11).

What is the acceptable steam velocity in a pipe? ›

Steam velocity of 45 to 50 m/sec is preferred. Temperature drop of 8-10 deg at the landing point is to be considered. Pressure drop should not exceed 1-2 bar. You have to keep these figures and arrive the line size and superheat required at the supply point.

What schedule pipe should be used for steam lines? ›

1. Pipe 2 inches and smaller: Carbon steel, ASTM A53, Grade B seamless, Schedule 40 for steam, Schedule 80 for condensate.

What pressure are steam boiler pipes? ›

A steam boiler operates at a very low pressure of 2 to 4 psi. Steam travels best at low pressures, whereas hot water is driven by a pump. Regardless of the type of system, a pressure-reducing valve should be installed at the main water inlet.

What is the best pipe for a steam line? ›

So, Alloy steel is used as the steam piping material for temperatures above 427°C as it has better material properties at elevated temperatures. Carbon steel pipes are suitable for steam at a temperature below 427°C. The piping standard used for saturated steam according to IBR is: A106 Grade B Seamless Schedule 40.

What is the pressure rating for steam pipes? ›

1. Steam Piping Ratings of Boiler Systems. In most states and jurisdictions, steam piping is classified as high pressure piping when it exceeds 15 PSIG.

How thick is a Schedule 40 steam pipe? ›

Sch40 on a pipe means that it can hold 40 kg of pressure. It's shown by a standard thickness of 4 mm.

Which way should a steam pipe slope? ›

Steam pipe lines should be designed with a slope of about 2-3 mm/meter in the direction of the steam flow. This facilitates smooth flow of condensate formed to the next Drain Trap and thus plays an important role in avoiding Water Hammer.

What is the allowable pressure drop in a steam pipe? ›

Two principal factors determine pipe sizing in a steam system: 1. The initial pressure at the boiler and the allowable pressure drop of the total system. The total pressure drop in the system should not exceed 20% of the total maximum pressure at the boiler. This includes all drops — line loss, elbows, valves, etc.

How should a steam pipe be supported? ›

Best Ways To Anchor and Support Steam Pipes
  1. Get the Proper Anchors. One of the best ways to anchor steam pipes is to do it with anchors that are strong enough for your application. ...
  2. Allow the Right Movement. ...
  3. Choose the Right Number of Supports.
Sep 8, 2023

What pipe velocity is too high? ›

Many engineers then apply a rule of thumb that says to use a velocity of 1.5 to4 m/s. Higher velocities mean higher pumping cost and possibly damage to the piping due to erosion or water hammer.

What is the rule of thumb for pipe flow velocity? ›

The general rule of thumb is to maintain a velocity below 5 ft/s (1.5 m/s). Gravity (g) and the slope of the pipe. An increase in slope decreases the pressure due to gravity. Pipe Diameter (D): The larger the pipe diameter is, the slower the flow velocity will be.

How to measure steam pipe diameter? ›

Take a string or flexible tape and wrap it around the pipe. Make a mark and then measure how long the string or tape is. Once you have the string's length you'll need to divide that measurement by pi (pi= 3.1415) to find the pipe's diameter.

What is boiler proper piping? ›

Boiler Proper Piping (BP) follows the guidelines outlined in the ASME Boiler and Pressure Vessel Code Section I. This includes all internal tubes and piping within the boiler, such as downcomers, risers, and superheater tubes.

What type of fittings for steam pipe? ›

Steam pipe fittings are now categorised as steel fittings BS EN 10241:2000 and are available in what are termed as black and galvanised. The so call black steam pipe fittings are actually just bare metal and the galvanised version are hot dipped galvanised fittings.

What pipe is used in boilers? ›

Due to the high pressure application, only seamless pipes and ERW get used as boiler products. Boiler pies are available in carbon steel, alloy, and stainless steel options. The Outer Diameter of boiler pipes varies from 6 mm to 1250 mm. Boiler pipes have a low thickness ranging from 1 mm to 50 mm.

Which pipe is good for steam? ›

Carbon steel pipes are suitable for steam at a temperature below 427°C. The piping standard used for saturated steam according to IBR is: A106 Grade B Seamless Schedule 40.

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