C.I. Boilers

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Cast-Iron Boilers

Print Date: 1/15/2009 1:34:34 PM

1. Description and Overview Cast-iron boilers may be used in steam heating or hot water heating applications within the scope and service restrictions of ASME Section IV.Section IV service restrictions limit steam boilers to pressures not exceeding 15 psi andhot water boilers to pressures not exceeding 160 psi and/or temperatures not exceeding250°F.

Cast-iron boilers can be constructed in different configurations. The three most commondesigns found in use are:

n Vertical Sectional – made up of individual cast iron sections assembled so thesections resemble slices in a loaf of bread. This is probably the most commonconfiguration.

n Horizontal Sectional – made up of individual cast-iron sections assembled so thesections resemble a stack of pancakes.

n One Piece – a single casting with no assembly joints. Another term used todescribe this design is monobloc. This type of cast-iron boiler is usually small insize.

Sectional boilers are typically assembled with tapered connections called push nipples or elastomeric-type gaskets between the sections to seal the water-containing chambers.

Another type of assembly uses external headers to connect the water containingchambers.

Cast-iron boilers can be found in almost any application where heating boilers are used.They are popular replacements for large welded steel boilers which may have beeninstalled as the building was being constructed. Cast-iron sectional boilers can usually beinstalled in existing boiler rooms by moving the individual sections through doors or window openings. A very large boiler can be assembled in this manner withoutmodifications to the building structure.

There will be two pieces of information missing from a cast-iron boiler nameplate: aNational Board registration number and the year built. Cast-iron boilers are not registeredwith the National Board, and ASME Section IV makes no provisions for a year of construction to appear on the nameplate. Since most inspection forms ask for a year of construction, the inspector will have to estimate. If the boiler is original to the building, theage of the building would directly correspond to the age of the boiler. If the boiler is areplacement, the inspector will have to question the owner to determine its age.

2. Appurtenances, Settings, and Piping Steam boilers must have at least one safety valve

of 4The National Board of Boilers and Pressure Vessel Inspectors

1/15/2009http://www.nationalboard.org/PrintPage.aspx?pageID=31&ID=34



with a set pressure not to exceed 15 psi. The safety valve inlet must not be smaller thanNPS 1/2 nor larger than NPS 4-1/2.

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. Thesafety relief valve inlet must not be smaller than NPS 3/4 nor larger than NPS 4-1/2. Theminimum relieving capacity of safety or safety relief valves must equal or exceed the

maximum output of the boiler. Cast-iron boilers constructed since 1943 will haveinformation on the nameplate indicating the minimum required safety or safety relief valvecapacity. Cast-iron boilers constructed prior to 1943 may not have that information. Inthose circumstances, the inspector must estimate the maximum output of the boiler. Gasor oil burners generally have a rating plate or label containing the Btu output of theburner. A generally applied guideline for older boilers is to use 80% of the maximumburner output as the maximum boiler output. Boilers fired with solid fuel such as coal or wood will be extremely difficult to estimate, since there is no way for the inspector tocalculate the cast-iron boiler heating surface. In those cases, the inspector shouldrequest the boiler owner/user perform an accumulation test in accordance with HG-512(a), or a maximum burned fuel evaluation in accordance with HG-512(b) and Appendix B.These procedures should only be used if the safety or safety relief valve capacity is in

doubt.

Safety or safety relief valves must be installed so the spindle is in a vertical position.

More information on safety or safety relief valve requirements can be found in ASMESection IV, HG-400 and HG-701.

Each steam boiler must have:

n a pressure gage with an internal siphon or a siphon in the gage piping (HG-602);n a water gage glass, or for specific boilers, a Bull's-Eye type gage glass (HG-603);n 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);

n 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).

Each hot water boiler must have:

n a pressure or altitude gage (HG-611);n a thermometer (HG-612);n

two temperature controls (if the boiler is automatically fired); one is considered theoperating 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);

n an automatic low-water fuel cutoff – if the boiler is automatically fired and has a heatinput greater than 400,000 Btu/hr (Note: some jurisdictions require an additional lowwater fuel cutoff with a manual reset switch)(HG-614)

n provisions for thermal expansion (HG-709).

Clearances on the front, rear, sides, and top of all cast-iron boilers for operation,





maintenance, and inspection shall meet jurisdictional requirements. If no jurisdictionalrequirements exist, then the boiler manufacturer's requirements shall be met.

All cast-iron boilers should be installed on foundations or supports suitable for the weightof the boiler and its contents. The foundation or support must also be unaffected by theheat of the operating boiler.

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

3. Common Observations and Problems Cast-iron boilers typically have a few inherentproblems. The inspector should always look for water leaks at the connecting joints of sectional boilers. The inspector should request the removal of the sheet metal casing anytime there is evidence of leakage and the leakage cannot be traced to an external source.

The most common problem associated with cast-iron boilers is cracking due tooverheating or thermal shock. Overheating occurs when the boiler is allowed to operatewith low-water conditions or poor circulation caused by sludge concentrated in the lower

water passages of the boiler. Thermal shock can occur when a boiler is overheated andcold water is added in an attempt to raise the water level. Under those circumstances,cracking is usually the least that can happen. The worst that can happen is an explosionwhich shatters the cast-iron boiler into many pieces and cause destruction and injury.

Sectional cast-iron boilers use long rods, threaded on both ends, called draw bolts. It isnot unusual for these draw bolts to appear loose when the boiler is cold. When the boiler is operating, the heat will cause the boiler to expand which tightens the draw bolts. Aloose draw bolt on a hot boiler should be investigated by a competent cast-iron boiler service/repair company.

4. Inspectiona. External – while in operation

Upon entering the boiler room, the inspector should perform a general assessmentof the boiler, piping, controls, fuel system, and combustion air supply. The inspector should then:

n review the current operating certificate (if one was issued in the past) andcompare the information to the associated boiler and its nameplate;

n compare the safety or safety relief valve nameplate data (set pressure andrelieving capacity) with the boiler nameplate to ensure the safety or safetyrelief valve is adequate for this installation;

n inspect the safety or safety relief valve operation as described in the NationalBoard Inspector Guide for Pressure Relief Devices; n 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;

n inspect the pressure or temperature controls as described in the NationalBoard Inspector Guide for Operating Controls;

n check the pressure or altitude gage reading (if there is a reason to questionthe accuracy of the gage, it should be replaced or recalibrated);

n check the thermometer reading on hot water boilers (if there is a reason to





question the accuracy of the thermometer, it should be replaced or recalibrated);

n check the water gage glass to ensure it provides a clear indication of thewater level in a steam boiler (Please see the National Board Inspector Guidefor Water Level Controls and Devices.);

n look closely for leaks at all pipe connections associated with the boiler;n look closely for leaks from the boiler and the joints between cast-iron sections;

n instruct the owner or owner's representative to repair any leaks which mayhave been discovered (if a leak is detected as a result of a crack in the castiron, there is no acceptable repair except replacement of the cracked section);

n look for evidence of overheating (this may be difficult to detect on a cast-ironboiler; warped external sheet metal casings with scorched paint is usually areliable indicator);

n witness any pressure test required by the jurisdiction; andn inspect the fuel-burning apparatus as required by the jurisdiction (for example,

some jurisdictions mandate compliance with ASME CSD-1).

b. Internal

Internal inspections of cast-iron boilers can prove to be difficult or almostimpossible. Threaded plugs on the cast iron boiler could be removed, but theinspector will see very little past the immediate vicinity of the opening on many castiron boiler designs. In addition, the threaded plugs are sometimes heavily corrodedwhich virtually "welds" them to the cast iron. Removal of threaded plugs in thiscondition may damage the cast iron irreparably. Some boilers may have valvesinstalled in the lowest threaded openings of the boiler to facilitate draining and/or flushing of the boiler. If valves are present, the inspector can ask for them to beopened briefly to observe the condition of the water. If no water is present when thevalves are opened, this could be an indication the lowest portion of the boiler isfilled with sludge. The inspector is advised to follow the jurisdiction's requirementsfor internal inspections of cast-iron boilers.

Float-type low-water fuel cutoffs and water-feeding devices (if applicable) must bedisassembled so the inspector can observe the condition of the float, floatmechanism, and the float chamber.

Threaded plugs in the piping connecting a water gage glass, water column, andlow-water fuel cutoff to a steam boiler must be removed to allow inspection of thepiping to ensure there is no blockage.

5. Miscellaneous Information Additional information to aid inspections of cast-iron boilerscan be found in the following publications and sources:

n National Board Inspection Code n ASME Section IVn ASME Section VIn ASME CSD-1n Manufacturer's Installation, Operation, and Maintenance Documentationn Jurisdictional Laws, Rules, and Directives



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