1. Drum Level Instrumentation and The ASME Boiler Code Requirements 2013
This presentation is focused on the requirements from Section 1 of the ASME Boiler and Pressure Vessel Code, as it relates to water gage glasses, water columns, indirect (remote) level indicating devices, isolation valves, piping considerations, the position (location) of these instruments, level switch requirements and other details.

2. Topics Direct and Indirect Reading Instruments
ASME Code Section 1 Requirements for Drum Level Instrumentation
Water Columns and Water Gage Isolation Valves
Prohibition of Structural Webs in Water Gage Glasses
End to End Reflex Type Water Gages
Magnetic Level Gages
Code Design Requirements for Isolation Valves
Level Switch requirements for HRSG applications
Low Water Cutouts
Common Code Violations
Recommendations for Level Instrumentation Piping
These topics include a review of the essential requirements for water gage glasses, along with other topics, which became in effect within the past 5 years.

3. ASME Code General Terms
Direct Reading Gage
Remote Level Indicator
Indirect Reading Gage
The only direct reading drum level gage is a glass gage.
The common Indirect reading water level indication systems may be of the following types: differential pressure, conductivity probe type systems with a control unit and remote display, magnetic level indication systems designed with a float in a stainless steel chamber, and Guided Wave Radar.
Glass Gage

4. Direct Reading Gage Glasses
Bi-Color
to 3000 PSI
Prismatic
(Reflex)
to 350 PSI
Tubular Glass
to 250 PSI
Flat Glass
(Transparent)
to 2000 PSI
There are four types of direct reading water gage glasses, as follows:
Tubular, Prismatic (also known as Reflex), Flat Glass (Transparent) and Bicolor (Ported) type.
We do not suggest tubular glass for permanent installations. Tubular glass offers the least protection for plant personnel, and should only be used for boil-out or chemical cleaning purposes.
Prismatic water gages often do not require any illumination accessories. These gages are easily viewed in areas with sufficient ambient lighting.
Flat Glass water gages should be installed with illumination accessories, in order to adequately read the level. These gages are designed with inner mica shields,
which reduce an observers ability to read the level, when installed without back-lighting. These lighting accessories are designed to illuminate the gage from behind the gage in a manner, which illuminates the depth of the meniscus (water line), and enhances the line to a star-like brightness.
Bicolor water gages are generally the only option for applications in excess of 2000 PSI. However, many uses apply this technology on low pressure applications, due to the ease of reading the level.

5. End-to-End Reflex Gage Glasses Are Permitted
PG.60.1 Clarifies the use of multi-section gages without overlap, due to the light refraction principle
Reflex (Prismatic) water gage glasses provide a distinct black color at the water line and below. Therefore, they do not require an overlap, because there is no mistake in reading the level, if the actual level happens to be in a void area. Whereas, a Flat Glass (Transparent) type gage could be misinterpreted without overlap, since steam and water are both clear in color.

6. Structural Webs are Prohibited From Flat Glass Gages Designs
These Webs may mask the actual location of the water level
The risk of Masking the level is enhanced on elevated gage glass installations
The reason for this code definition is to prevent the installation of a water gage that may cause an operator to misread the actual level. These webs can appear to be the level, especially when the gage is viewed from a distance.
A properly designed boiler water gage glass doe not require structural webs. Light weight Gage glass designs with structural webs that were originally intended for process fluid service applications are prevented from being used on boilers, due to this Code statement in PG-60.

7. Flat Glass Transparent Type Water Gage Glasses
Typical View of Water Level with no obstructions in the viewing area. The gage must be illuminated, as needed for the level to be readily visible by the operator.

8. Bi-Color Water Gage Principle of Operation
Water shows GREEN Steam shows RED.
(Light refracts differently through water than steam with glasses on specific angles)
Bi-Color Gages must be outfitted with an
illuminator to be Code Compliant

9. Indirect (Remote) Level Indication Technologies
Conductivity Probe Type
Level Indication System
Magnetic Level Gage
(equipped w/ 4-20 transmitter)
The common Indirect reading water level indication systems may be any combination of the following types: differential pressure, conductivity probe type systems with a control unit and remote display, magnetic level indication systems designed with a float in a stainless steel chamber, and Guided Wave Radar.
PLUS OTHER TECHNOLOGIES
Differential Pressure Transmitters
Guided Wave Radar

10. Remote (Indirect) Level Indicators
All Differential Pressure and Guided Wave type Indirect Level Indication instruments must be installed and programmed to the manufactures instructions to prevent indication errors.
Precautions must be taken to prevent adverse effects from freezing conditions on the level sensing components
Insulation on all piping is recommended, except on the Condensate Pots for DP transmitters. Install cages or guards to protect personnel, if service area is confined
If Condensate Pots are insulated, they will not respond form condensate. Heat tracing is recommended on applications in climates with the potential for freezing.

11. ASME Boiler Code Requirements
Water Gage Requirements:
Operating up to 400 PSIG
One Direct Reading Gage Required
(which must be kept continuous service)
Operating over 400 PSIG
Two Direct Reading Gages in service OR
Two Remote (Indirect) Level Indicators
On Continuous Display for the
Operator and One Direct Reading Gage
(Which may be Isolated but kept in serviceable condition)
The Code mandates water gage glasses remain in service at all times on applications up to 400 psi, because these boilers tend to be located near more people, such as industrial plants, Universities, Hospitals, Schools. Therefore, having the most obvious and accurate water level instrument in continuous service drastically improves the safety of operating these boilers.
“Continuously display” means that an operator must NOT have to strike a key for level information to appear on the monitor screen. The 2 independent level indicators must be continuously displayed.
It is common practice for many plants to continue to operate with water gage glasses on applications above 400 psi, even though they have 2 indirect level indicators on continuous display.

12. Code Requirements for Gage Glass Placement
This slide illustrates the ASME Code rules for the location of the visibility range limitations of a water gage glass, with respect to the piping between the drum and the water column.
The reason for this code definition is to prevent the installation of a water gage that does not fill to the top of the visibility or one that does not drain completely.
In essence, the maximum visibility of a water gage glass must not encounter the vessel connection piping. To meet this requirement, one could say the maximum “V”= vessel connection centers minus 1 pipe diameter. This provides a half pipe diameter of increased safety on each end of the visible range in the instrument from trapping or not reading a level due to pipe sag or incline.
Level “A” = Lowest Permissible Water Level, at which there will be no danger of overheating the vessel

13. Code Requirements for Gage Glass Placement
This slide illustrates the ASME Code rules for the location of the visibility range limitations of a water gage glass, with respect to the piping between the drum and the water column.
The reason for this code definition is to prevent the installation of a water gage that does not fill to the top of the visibility or one that does not drain completely.
In essence, the maximum visibility of a water gage glass must not encounter the vessel connection piping. To meet this requirement, one could say the maximum “V”= vessel connection centers minus 1 pipe diameter. This provides a half pipe diameter of increased safety on each end of the visible range in the instrument from trapping or not reading a level due to pipe sag or incline.
Gage Glass Visibility must not intersect Vessel connection pipe diameters

14. Water Gage Glass Placement Explained
1. Lowest Permissible Water Level- At which level there will be no danger of overheating (Level A).
2. Water Connection for Water Column- Must be 1” below low visibility point of gage glass and at least 1” NPT. The line must be level or slope downward from column to drum.
3. Steam Connection for Water Column-Same as 2 above. Except slope down ward from drum to column.
4. Steam Connection may come out of top of vessel- Centerline of steam connection would be at point marked “B”.
5.The lowest visible part of water gage glass-Must be at least 2” above the lowest permissible water level (Level A).
6. The highest visible part of water gage glass-Must be at least 1” below center of steam connection.
7. Gage cock connections- Must not be less than 1/2” pipe size and located within gage visibility range “V”. (Gage cocks are no longer required by ASME Section 1.)
This slide explains the detail for the previous slide.

15. ASME Code References Water Columns (PG-60.2)
- 1” min. connection size for water column to boiler (PG )
- 3/4” min. drain connection size (PG )
Stainless Steel is prohibited for the construction of water columns (PG-12.3)
Water Level Indicators (PG-60.1)
* Water Gage Glass Requirements ( PG )
* Gage Glass & Connections ( PG-60.3)
* 3/4” min. connection size for Remote (Indirect) level indicators (PG )
* Highest visible permissible water level (PG )
* Lowest visible permissible water level ( PG )
* Stainless Steel for Gage Glass Body (PG-12)
* Magnetic Level Gage Chambers permitted up to 900 PSI (PG-12), as of 2007
* 1” Gage overlap requirement for Transparent Gages (PG-60.1), since 1996
* Transverse or Cross Web Structural Webs are prohibited from use in the construction
of Transparent type Water Gage Glasses, which may obstruct the view of the level
(PG60.1), as of 2009
Ball Checks in Water Gages Valves considered to be a user option, if specified, must meet the
Code requirements (Automatic Shut Off Valves – Appendix A-18)
These subsections outline the most common concerns about drum level instrumentation. The Subsections numbers identified on this slide may all be located in Section 1 of the ASME Boiler and Pressure Vessel Code.
Ball Checks in Water Gage glasses are designed to restrict the flow to a water gage glass, in the event of breakage or significant leak. The Code requires a vertical rising ball in the lower water gage valve and the ball is not permitted to shut the flow completely, which is intended to prevent sticking or trapping water in the gage glass. We meet this requirement by making an irregular surface on the ball check seat. This greatly reduces flow to the gage glass and prevents complete shut off.
However, the use of ball checks does reduce the effect of conducting a Blow down of the gage. Some users report the need for more frequent gage glass repairs, due to contamination on applications with ball checks.
A good safety measure is to install chain operators, so the water gage valves may operated from a safer distance, in the event of a leak.

16. ASME Code References Gage Cocks → Switches not permitted
Gage Cocks (Trycocks) are not required (PG-60.4), since 1991
Many Operators continue to rely on Gage Cocks
Magnetic Water Level Gage: permissible for applications up to 900 PSI
External switches are
not permitted for control
Purposes, such as
Low Water Cutouts
(PG.12 and PG.60)
Gage Cocks →
Many operators continue to use Gage Cocks (Try Cocks) on water columns, even though that have been eliminated from the Code for 20 years.
The restriction against the use of external level switches on Magnetic level gages prevents an installer from casually installing a control switch at an inappropriate level on this device.
Switches not permitted

17. Code Limitations for the most commonly used materials for Instrumentation (Pressure Parts)
SA-278 Cast Iron to 250 PSI
SB-61 Bronze to 450 PSI
SA106 Carbon Steel Pipe or SA105 Forgings to 3000 PSI
Specified Grades of Stainless Steel
These are the most common materials applied to the construction of drum level instrumentation. Section 2 of the Boiler Code identifies the properties of the permissible materials, including the pressure and temperature limitations.
Stainless steel is permitted for the construction of water gage glasses and Mgnetic level indicators. A list of the acceptable grades of stainless steel is located in PG-12.3 in Section 1 of the Code.

18. Water Columns Cast Iron Water Columns are permissible up to 250 PSI
Fabricated Steel Water Columns are used for applications up to 3000 PSI
Three types of Water Column Functions
No Alarm for the sole purpose of supporting one or two water gage glasses
Float Alarm Type
Electrode (conductivity Probe) Type for
Alarms and Cut Outs (Trips)
The Code does not mandate the use of a water column to support the required water gage glass. However, the Code does define the rules for construction of water columns.
In may situations, the use of a water column is the only way to adapt a gage glass to the vessel and achieve the required visibility range. The water column and lower water gage valve must both be installed with drain piping and valve to a safe discharge location.

19. Water Columns and Standpipes (Tie Tubes)
Water Columns are not required on Power Boilers by ASME Boiler Code, but when specified, must be designed and manufactured to comply with Code
Water Columns are considered to be a Standard Pressure Part or Standard Welded Part as defined in Section 1: PG-11 of the ASME Boiler Code. Therefore, a Code stamp for manufacturing is not required. The use Code recognized materials and applicable welding procedures are a must.
The terms Water Column, Tie Tube, and Standpipe, all refer to a vertical pipe manifold for the primary benefit of attaching one assembly onto a boiler with one set of connections

20. Always Install Chain Operators for Operator and Plant Safety
PG requires an accessible operating mechanism from the isolation valves to the operating floor or platform
When setting up chain pulls on quick closing lever actuated valves, position the levers, so they aim downward toward a 5:00 position when the valves are closed.
The ability to reposition the levers on this type of valve, when closed, enables this style of valve set to be linked together.
When installing chains on chain wheel operated valves, never link the 2 valves together with one loop of chain, because one valve will likely close ahead of the other one, due to the relative relationship of the actual stem position for seat to the teeth on the chain wheel. Chain wheel valves should be operated independently to enable the operator to achieve complete shut off of each valve, by operating them independently.

21. Globe Valves for Isolation and Drain
Globe type valves are now permitted if the lowest edge of the seat is at least 25% of the port diameter.
(Ref: PG )
In-line flow prevents sediment or condensate traps, which can lead to false level indication with traditional Globe valves
Traditionally designed globe valves have a pocket are in the body, which can trap with sediment and water (condensate). The use of the Code required style (Y patter type shown) prevents blockage. One quick method of examining a valve for this application is to have the ability to push a small wire through the valve (in a straight line) when it is fully open.
The use of incorrect style globe valves, especially in the steam piping may result in a false indication of level in the instrument, especially if the stem is oriented vertically.
Incorrect
Correct

22. (equipped w/ 4-20 transmitter)
Magnetic Water Level Gages Concerns
Magnetic Level Gage
(equipped w/ 4-20 transmitter)
Magnetic Level Gages illustrated on this slide show an indication scale for a process fluid and a correct scale for power boiler applications.
For Process
For Power Boilers
Indication Scale

23. Code Issues and Concerns for the Use of Magnetic Level Gages on Boiler Drums
Acceptable as an acceptable Indirect Reading for applications Gage up to 900 PSI (Ref: PG12.2)
The Indication Scale must follow ASME guidelines (Ref: PG &
PG60.3.3)
May not be used to support a water Gage glass, due to prohibition of stainless steel construction for water columns. Ref: PG-12.3
No accessories are permitted to be attached for control purposes
(No Trip Switches). This device must be used for indication only.
Ref: PG
NOTE: The use of a Magnetic Level Gage does not replace the Code requirement for a Direct Reading Water Gage Glass on any Power Boiler Drum designed to meet the ASME Section 1 Boiler Code
We suggest that any user of a magnetic water gage for steam service, should inspect the float after one month of service, to verify that there is no build up of contaminants. If the float is clean, then no future routine maintenance will be required. If the float is contaminated, then periodic inspections will be required.

24. Concerns for the Application of Magnetic Water Gages on Boiler Drums
The float design is based on the operating conditions(customer specified), not the boiler design conditions. Therefore, if the boiler is operated at a pressure lower than the planned operating pressure, the Magnetic Gage reading will be higher than the actual drum level.
If the user has poor water quality, the potential exists for iron particles to attach onto the float. This will result in a heavier float, with an inaccurate level reading.
The risk of indication error caused by operating a Magnetic Level Gage at a much lower than intended pressure has been greatly reduced by the Code limiting the application pressure to 900 PSI.

25. Low Water Cutouts – CSD-1
• Two devices are required on CSD-1 applications (Controls and Safety Devices for High Pressure Steam Boilers– ASME) Subsection CW-140
• The two devices must be in separate chambers or one of them may be inserted directly into the boiler
Minimum connection pipe size is 1” with vertical drain no less than ¾ NPS
The devices are not defined in Section 1 of the Code.

26. Low Water Cutouts Continued
• One control must be set to activate ahead of the other one
The cutout circuit may include a time delay not to exceed 90 seconds or the manufacturer’s recommendation (whichever is less)
A Manual Reset function may be applied to the lower of the 2 controls, with a maximum delay of 3 minutes, after the fuel has been cut off
The cutout circuit may incorporate a time delay not to exceed 90 seconds or the manufacturer’s recommendation (whichever is less)
A manual reset circuit requires an operator to active a switch in order to satisfy the low water cutout circuit. The concept is so the operator confirms there is a safe water level in the gage glass, prior to activating the reset switch.

27. Requirements for Level Switches on HRSG’s
The Code now requires Drain Pots to be installed in the Boiler Proper or Boiler External Piping either upstream or downstream of the Desuperheater to ensure malfunctions of the devices will not allow water to enter hot boiler components. These drain pots shall include automatic detection of water and automatic operation of the drain pot valves. Drain pots with single element level control with delay to close are an acceptable method of detecting and removing spray water. Consult ASME Code Section PHRSG-4 for more details
This application is not directly connected to the topic of drum level instrumentation, but the use of conductivity probes is often applied to this application.
Example Drain Pot Installation

28. HRSG Requirements for NFPA 85 Compliance
Water Level in each drum is continuously monitored and recorded or logged (Section )
Operators receive audible and visual alarms for low water level (Section )
Duct Burner Master Fuel Trip from Low Water Level on HP Drum section ( )

29. Proper Care Recommendations - Section 7
Check water level in 2 or more instruments prior to start up and verify when a deviation is observed
Keep Water Gage Glasses clean and easy to read, confirm there is no deviation that could be mistaken as water level
Water Gages should be properly illuminated for easy observation
Excessive blow down may cause premature wear of the gage internals
Verification of high and low water alarms is critical to the prevention of carryover or damage to drum internals

30. Proper Care Recommendations - Section 7
Verify there are no leaks around the level instrumentation, piping, related isolation valves, or water column. Leaks may affect the accuracy of the indicated level and eliminating any leaks will prevent a hazard
Check external instrumentation piping for any missing insulation
Risk of damage to equipment by steam cutting may also be prevented with routine inspections of the valves, and external piping, in addition to regular inspection of the water level.

31. Good Practice Recommendations for Level Instrument Piping
All piping from the drum to the water level instruments are to be insulated, for the following reasons:
1. Provide safety for plant personnel
2. Increases level accuracy
3. Reduce excess condensate formation
Any slope in the piping should be downhill on the steam line & uphill on the water line from the drum.
Piping from Drum to Level Instruments should be kept to a minimum < 6 Ft
Insulation can actually improve the service life of a water gage glass by reducing the amount of condensate that forms in the steam piping and erodes the mica shield component of the gage glass. Less condensate formation equals less wear.
Minimal pipe runs reduce temperature loss and may increase level indication accuracy in the instrumentation.

32. Common Code Violations and Concerns
Isolated Inoperable Water Gages
Missing Water Gage Glasses
Missing Illumination from Ported type gages
Inadequate display of remote Level Indicators in the control room combined with isolated gages
Unfortunately, too many of these violations exist on boilers. Users must be educated with the actual Code requirements in order to maximize plant and personnel safety.

33. Common Code Violations and Concerns Continued
Contaminated Water Gage Glasses
that prevent viewing the actual level (meniscus line)
Multiple Section Flat Glasses without the Code required overlap
Poor Maintenance Practices
A contaminated water gage can result in a stain at the water level line, especially on neglected tubular glass applications. A white color on the inside of the glass may occur on higher pressure water gage glasses when the mica shield has deteriorated. This signals an immediate repair of the gage must be conducted and the gage glass must be isolated immediately.

34. Source: The National Board of Boiler and Pressure Vessel Inspectors
Annual Violation
Report
The data Illustrates
Boiler Controls as
the primary source
of violations
This report illustrates an alarming number of violations for Boiler Controls that should concern all of us. Many users lack training and support, which would reduce these statistics.
Beginning in 2012, the inspectors will be detailing the causes of the violations for boiler controls. This will enable us to extract the actual data related to water gage glasses, water cutouts, and other causes.
Source: The National Board of Boiler and Pressure Vessel Inspectors

35. Drum Level Instrumentation
This photo illustrates properly installed chains on the water gage isolation valves. Proper drain piping on the water gage valves and the water column. You can see the C-R nameplate on the water column.
On the right side of the drum, there is an Electrolev column and differential pressure transmitter sensing lines.
The drain piping on the lower right side of the drum should not be plugged with the trap in the piping. The low point must have a valve. This is a Code violation and has since been remedied by the customer.
Note: Photos are helpful for discussion

36. Photo of Serious Installation Error
This water column was installed incorrectly with the steam and water inlet piping sloping downward. This dangerous installation was never placed in operation. The low water alarm and low water cutout probes would have indicated trapped water in the piping and the gage glass would respond the same.
We were notified of this installation, prior to operation. The next slide illustrates the remedy.
Code Violation and Operation Risk to Boiler

37. Photo of Corrected Installation
The water column was relocated to the correct (originally intended) position.
Now the position of the gage glass and conductivity probes in the water column are in the correct position relative to the drum.

38. Top Questions for Users
Are you having any operational issues with Water Gage Glasses on Boiler Drum applications?
What instruments are installed for the display Drum Level Indication in the Control Room?
Are the water level limit controls on your boiler applications working properly and tested regularly?
Does the existing Drum Level Instrumentation meet the Code for the Design and Operating Pressures of your Boiler Drum?
These questions are intended to prompt a response from the user or operator and raise the concern to verify the Code compliance and maximize safety.

39. Summary Recommendations for Drum Level Instrumentation Installations
for Users
Specify or Install Code Compliant Designs
Examine Piping and isolation Valves
Consult with the Insurance Underwriter or Plant Safety Department for plant requirements, which may exceed Code minimum
Always follow the OEM maintenance instructions for the most accurate and reliable information
Consulting with the plant safety personnel or insurance carrier will often result in support to remedy any existing instrumentation needed to meet Code.
Encourage the user to correct any concerns.

40. Summary
Your time and attention to this information is appreciated, along with your contributions to Operator and Plant Safety of Power Boilers
Questions