Technical Information

Power Boilers Fall Under the Jurisdiction of the ASME

ASME B&PVC Section I — PG-2.1

The rules of Section I are applicable to boilers in which steam or other vapor is generated at a pressure of more than 15 psig for use external to itself.

Note that ASME B&PVC Section I does not allow for a "size exemption."

Deionized Water Must Be Used with a Stainless Steel Steam Generating Power Boiler

ASME B&PVC Section I — PEB-5.3

Electric boilers of the immersion element type may be fabricated of austenitic stainless steel type 304, 304L, 316, 316L, and 347 of any material specification listed in PG-6 and PG-9, provided that a precautionary statement indicating that the boiler shall be operated using only deionized water, having a maximum conductance of 1 microSiemen per cm (1 µS/cm) [minimum specific resistivity of 1 megohm per cm (1 MΩ/cm)], is clearly marked on the boiler in a visible location.

The "U" Designator Is Not Acceptable for an Electric Steam Generating Power Boiler

• As stated above, these boilers are specifically covered in Section I of the ASME B&PVC.
• The "U" designator is covered in ASME B&PVC Section VIII.
• ASME B&PVC Section VIII U-1(c)(2)(a) states that vessels within the scope of other Sections are not to be included in the scope of Section VIII.

Some manufacturers will try to use ASME B&PVC PEB-3 as justification for use of the "U" designator. ASME B&PVC Section I PEB-3 states the following:

The boiler pressure vessel may be constructed in compliance with the ASME Pressure Vessel Code Section VIII, Division 1, rules for unfired steam boilers [UW-2(c)] subject to the conditions specified in PEB-3.1 through PEB-3.4.

This assertion fails on at least two accounts:

• As seen in ASME B&PVC Section VIII U-1(c)(2)(a), vessels within the scope of other Sections are not to be included in the scope of Section VIII.
• These power boilers are fired steam boilers, not unfired steam boilers. As a result, ASME B&PVC Section I PEB-3 is invalid for this application.