Answers to submitted questions

Requests addressed to CEN/TC 269 MHD before 2009 have been considered in the revisions of the standards concerned or are still under consideration in the responsible WG.

Request #01-2009:

If EN 13445 may not be used for design of steam generation, to which code may an electric boiler be designed? EN 12953 refers to shell boilers, and EN 12952 to water tube boilers. As an electric boiler consists of the shell, two dished ends, the nozzles and its support this does not fit into either of the two EN boiler codes.

Answer: An electric boiler may be designed according to European standards series EN 12953 about shell boilers.

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Request #02-2009:

EN 12953-1:2002-05 "Shell boilers - Part 1: General" says in its scope, 1.2, 2nd paragraph, that "this European Standard specifies requirements for both directly fired and electrically heated boilers including low pressure boilers...".

EN 12953-6:2002-05 "Shell boilers - Part 6: Requirements for equipment for the boiler" has in 5.9 included requirements for electrically-heated boilers.

EN 12952-3:2001, 10.2.1, Figure 10.2-1 and Figure 10.2-2:

It is clear that torispherical ends have to fulfil the requirement of rik ? 2 es, based on Figure 10.2-1. Is this also applicable for semi-ellipsoidal ends? As Figure 10.2-2 does not have this requirement, it is assumed that rik ? 2 es is only required for torispherical ends.

Answer: Yes, semi-ellipsoidal ends do not have to fulfil the requirement of rik ? 2 es.
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Request #03-2009:

EN 12953-3:2002, 9.1.2, Figure 9.1-1 and EN 13445-3:2002, 7.5.3.5, Figure 7.5-3:

1) Is there a calculation method for determining the shape factor C for unstayed dished heads without openings from Figure 9.1-1? The size of the figure and logarithmic scales make it difficult to read the shape factor with precision.

The shape factor C in EN 12953-3 does not correspond to the beta value in EN 13445?3:2002, 7.5.3.5 (factor ? in Figure 7.5-3) which appears to give conservative values for the end thickness.

Answer: Currently under discussion.
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Request #04-2009:

EN 12953-3:2002, 10.2.4, 5th paragraph:

It is stated that: “Two or three adjacent stay tubes can be considered as one point of support, in which case the circle shall pass through the geometrical centre of the stay tubes (see figure 10.2-3)”

This is with regard to drawing circles. But what with regard to draw the loaded area to be supported by the stay tubes? It is not explicitly written but it must be evident that the two or three stay tubes shall be regarded also as one point of support so only one area has to be drawn for 3 stay tubes. The supporting tube cross sectional area will then be the sum of the two or three stay tube cross sectional areas supporting one(!) area.

A different approach would be to draw one area per stay tube but this seems not to be the intention. It would also not be reasonable because the three stay tubes are so close that they will deflect in longitudinal direction with same amount and therefore be loaded the same.

Answer: Currently under discussion
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Request #05-2009:

EN 12953:

We produce hot water boilers, shell type, in regime 70 °C to 90 °C with power from 25 kW to 2500 kW.

For boilers with power < 300 kW we apply EN 303-5:1999, Heating boilers – Part 5: Heating boilers for solid fuels, hand and automatically stocked, nominal heat output of up to 300 kW – Terminology, requirements, testing and marking and we have TÜV certificate under Module B1 for this kind of boilers according to CE marking.

But we have doubt about hot water boilers for solid fuel with power > 300 kW. Which EN standard is applicable for this kind of big hot (warm) water boilers?

Answer: For Stay tubes: please refer to NFE 32104
For solid fuel shell boilers: the EN 12953 could be applied if relevant. For the time being there is no information about a specific standard.
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Request #06-2009:

EN 12953-3:2002, 8.1.1.2, 3rd paragraph, 2nd sentence states:

"The distance shall be considered adequate if the outer edge of a branch or welded-on reinforcement, on a main body with a thickness ers£ 25 mm is at a distance of 2 ers and on a main with a body thickness ers ? 25 mm the distance is at least 50 mm from the weld edge."

EN 12953-4:2002, 5.13, 1st paragraph states:

"Openings in or adjacent to welded seams shall be avoided, especially if the seams are not stress relieved. The minimum distance from the centreline of the welded seam to the nearest point of the weld of the connection, or edge of the opening, shall be 60 mm, or four times the shell plate thickness, whichever is the larger."

Answer: During its next revision EN 12953-4:2002, 5.13, 1st paragraph shall be altered to:

"... or edge of the opening, shall be 50mm, or two times the shell plate thickness, whichever is the larger".


The two above requirements are not in agreement.
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Request #07-2009

Request on EN 12953-3, 10.2.9.3 (equation 10.2-4)

In the following equation of EN 12953-3 subclause 10.2.9.3 there is no explanation or value for the symbol fG.

Answer: For the formula 10.2-4 of EN 12953-3, with eg expressed in mm, h expressed in mm, W express-ed in N (force), f expressed in N/mm2, we can deduce that fG is a dimensionless number, such as a safety factor (safety coefficient), which is equal or above 1.
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Request #08-2009

Request on EN 12953-4:2002-05, 5.16.1, Note:

In the note it is written: "It is permissible to increase the limiting thickness to 40mm where the impact property of the material is at least 50 J."

It is not specified at which temperature this requirement shall be fulfilled. This needs clarification

Remark: In EN 10028-2:2009-06 "Flat products made of steels for pressure purposes - Part 2: Non-alloy and alloy steels with specified elevated tempe-rature properties", 8.2, Table 3 "Mechanical properties (applicable to the transverse direction)" the minimum impact energy KV (in Joule) is given at the three temperatures -20°C, 0°C and +20°C.

Answer: The impact energy of 50 J stated in the EN 12953-4:2002-04, 5.16.1, Note is given at a temperature of 0°C.

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Request #01-2010

Request on EN 12952-5:2001, subclauses 7.3.5, 7.3.6, A.1.4

If a bend of a piping system is manufactured by bending a straight tube it is physical impossible to reach required calculated wall thickness for intrados and extrados, respectively, at the bend’s direct ending. Therefore EN 12952-5 stipulates at A.1.4 that „Procedure test bends shall be bent to an angle of at least 90°. This shall be deemed to represent the minimum requirements for all bend angles. The thickness and DFC measurements shall be taken at 30° intervals from within this bend angle.

Answer: For clarification the following modifications to clauses 7.3.5, 7.3.6 and A.1.4 of the standard should be incorporated during the next revision:

7.3.5) Thickening at the tube bend intrados for tubes of nominal outside diameter above 80 mm up to and including 142 mm

The thickness at any point after bending, with the exception of a transition zone of 15° at the bend’s ending, shall not be less than that given by equation: …

7.3.6) Thinning/Thickening at the tube bend extrados/intrados for tubes of nominal outside diameter greater than 142 mm

For tubes above 142 mm diameter comparison shall be made directly with the calculated thickness given in 11.3 of EN 12952-3. The calculated thickness shall be stated on the drawing. At the tube bend intrados required wall thickness must be reached after transition zone of 15° measured from the tube bend’s ending. The value of wall thickness at the tube bend extrados must not fall below required wall thickness . At direct ending of the tube bend required wall thickness of the straight tube shall be proven.

A.1.4) Procedure test bends shall be bent to an angle of at least 90°. This shall be deemed to represent the minimum requirements for all bend angles. The thickness and DFC measurements shall be taken at the section of the tube bend’s center and from there on at 30° intervals towards both ending of the bend. Within a transition zone not exceeding 15°, measured from the direct ending of the tube bend, transition of wall thickness of the straight tubes to required wall thickness of the tube bend must have taken place. At the tube bend intrados the value of wall thickness between the two transition zones must not fall below required calculated wall thickness. The value of wall thickness at tube bend extrados must not fall below required wall thickness. At direct ending of the tube bend required wall thickness of straight tube shall be proven.

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Request #02-2010

Request on EN 12953-3:2002, subclauses 8.2.2, 10.2.10.2, 10.2.10.3

— Editorial problem in sub-clause 8.2.2, equation (8.2-2), in the German and French versions, the coefficient 2 has been deleted, the equation should be written as in the English version of the Standard:

For this efficiency coefficient the greatest outside diameter dob of an isolated branch shall be obtained when its wall thickness can only withstand the internal pressure (8.2-2)

— Contradiction between sub-clauses 10.2.10.2 and 10.2.10.3, see sentences below:

10.2.10.2

...

If the shell thickness ecs is calculated in accordance with equation (7.2?2) with a weld factor v = 0,85 the stress reduction factor x need not be considered.

...

10.2.10.3

...

The wall thickness of the shell shall be calculated in accordance with equation (10.2?5), including the stress reduction factor x (see equation (10.2?6));

...

Answer: Regarding the remark on the proposed editorial correction of 8.2.2, Equation (8.2-2): This equation is correct in the English and in the German version. Only the French version needs correction (figure "2" to be included in the formula).

The second part of the request should be discussed by CEN/TC 269/WG 2 for the next revision of the standard.

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