Profitable business by misleading?
PED-certified screw manufacturers?
There is confusion and pure misconceptions regarding what requirements
are to be imposed on fasteners included and contributing to pressure
resistance in pressure vessels and heat exchangers. This has been
exploited by certain international Notified Body companies, which see this
as a way to make money by issuing so called PED-certificate for screw
manufacturers.
Appro has now grown tired of these lies and misconceptions and want
once and for all establish what is right and wrong.
A screw manufacturer can not be approved within the requirements of
PED 97/23/EC. It is only the manufacturer of the pressure vessel itself
that must meet these requirements, including the CE marking.
Swedish Standards Institute position in the matter:
"A screw manufacturer can not be approved according to PED,
there are no certificates that give such approval." Otto Björnberg,
Project Manager, Materials Technology, SIS, Swedish Standards Institute
Motorgatan 2 | SE 442 40 Kungälv |Telephone: +46 (0) 303-24 34 40 | Fax: 0303-24 50 15 |info@appro.se | www.appro.se
The manufacturer of the pressure vessel has however, always the
responsibility of selecting a material for the screw that ensures that the
design of the pressure vessel meets the requirements in the PED
directives. The choice of materials in pressurized parts can only be
selected by one of the following options:
1. By using material which comply with standards that are harmonized
under the directive
2. By using material covered by the EAM (European Approval of pressure
equipment, materials).
3. By using material that the pressure vessel manufacturer assessed
appropriate and has issued a PMA (Particular Material Appraisal) for.
Note 1: Approved materials for fasteners to be found in the PED with
harmonized standard EN 10269.
Note 2: Refers to Article 11
Note 3: The use of a PMA is limited to a single application by a single
manufacturer.
The approval process would have to be repeated for each material and
product produced.
Motorgatan 2 | SE 442 40 Kungälv |Telephone: +46 (0) 303-24 34 40 | Fax: 0303-24 50 15 |info@appro.se | www.appro.se
When talking about mechanical properties, it is therefore important to
keep the component (screw) and the material separated. Many pressure
vessel manufacturers have here misunderstood or been misled by profited
Notified Body companies. The problem is further described under "double
classed material".
PED is however clear; the component and material shall be kept separate,
this is further clarified by 97/23/EC Guideline 7 / 8 and 7 / 19:
"The bolting parts are joining components. When these
components contribute to the pressure resistance, their materials
shall fulfil the relevant requirements of annex 1, section 4t.”
"The requirement in annex 1, section 4.3 is not however intended
for a component manufacturer, who is not a material
manufacturer in the context of PED, even if he modifies the
mechanical properties of the material."
Conclusion; the material inspection certificate shall be issued by the steel
mill and not by the screw manufacturer. The screw manufacturer should
only submit the certificate of inspection for the finished product and any
additional requirements from the pressure vessel manufacturer.
PED also require that the material manufacturer/steel mill has a proper
certification to ISO 9001 or equivalent.
This is described in Guideline 7 / 16:
"When the material manufacturer has a quality management
system, certified by a competent body, and when the field of
validity of the certification specifies production of materials
indicating the relevant material types".
Motorgatan 2 | SE 442 40 Kungälv |Telephone: +46 (0) 303-24 34 40 | Fax: 0303-24 50 15 |info@appro.se | www.appro.se
With this in mind, you have to be careful when buying from wholesalers
who have an import of fasteners from countries outside the EU.
Wholesalers/manufacturers across Europe stock these materials, so you
never know what you actually get when you order. Be sure to request
adequate identity-, quality- and inspection certificates.
Inspecta, a leading international provider of inspection and certification
services:
"Fasteners are not to be classified as material, but as components.
In order to prove the conformity to the PED of the pressure
equipment containing the component, the equipment
manufacturer will need relevant documents from the component
supplier "
Bo Lindblad, Inspecta Sweden AB
If identification and traceability can’t be guaranteed and secured through
a original material certificate issued by the manufacturer/steel mill, then
the component can’t be used in pressure vessels which are supplied under
the PED directives.
Therefore, be aware when wholesalers in the screw industry in their
product catalog, marketing themselves for “PED approved components”
with texts like:
"We cover pressure vessel requirements of EN 10269" or "We have
certification under TUV and ASME"
Of course, these allegations are completely false, material standard EN
10269 contains no pressure requirements at all.
And it's only the steel mill that can issue these material certificates and
not the screw manufacturer or a wholesaler.
Motorgatan 2 | SE 442 40 Kungälv |Telephone: +46 (0) 303-24 34 40 | Fax: 0303-24 50 15 |info@appro.se | www.appro.se
Double classed material
Another confusion that exists within the pressure vessel industry, is the
term "double classed". Some of the largest pressure vessel
manufacturers require that the chemical content and mechanical
properties of the fastener must cover and relate to two international
standards at the same time.
Often their material specifications describe that the screw must include
requirements for both ISO 898-1 and ASME SA193.
These standards are only requirements for product manufacturing,
properties of each property class/grade, testing and marking. Nowhere in
these standards is the material to be used mentioned, which of course is a
basic requirement in PED directives.
PED also describes some clarifications of essential requirements for safety
regulation in the selection of materials that must be withheld. It is
important to have a good margin in the choice of materials, in order to
secure a guaranteed consistent quality within tolerances.
Extracts from annex 1 ESSENTIAL SAFETY REQUIREMENTS PED 97/23/EC:
“Unless other values are required in accordance with other criteria
that just be taken into account, a steel is considered as
sufficiently ductile to satisfy 4.1 (a) if, in a tensile test carried out
by a standard procedure, its elongation after rupture is no less
than 14% and its bending rupture energy measured on an ISO V
test-piece is no less than 27 J, at a temperature not greater than
20 degrees ºC, but not higher than the lowest scheduled operating
temperature.”
This means that a fastener in class 8.8 doesn’t meet the requirements for
PED.
EN ISO 898-1:2009 is no longer harmonized or linked to PED 97/23/EC.
Of course, one can still invoke the requirements of EN ISO 898-1:2009, but
only for the product testing and marking. For the steel producer, the concept
of "double-classed material" does not exist.
Each material is unique, with its own chemical composition and mechanical
properties.
Motorgatan 2 | SE 442 40 Kungälv |Telephone: +46 (0) 303-24 34 40 | Fax: 0303-24 50 15 |info@appro.se | www.appro.se
When you compare different properties of common strength grades, it’s
clearly shown that 8.8 and B7 can not be classified under the same
requirements.
Note:
Fasteners conforming to the requirements of this part of ISO 898
are used in applications ranging from -50 °C to +150 °C. Users are
advised to consult an experienced fastener metallurgist for
temperatures outside the range of -50 °C to +150 °C and up to a
maximum temperature of +300 °C when determining appropriate
choices for a given application.
Grade
8.8
Property
Carbon (%)
B7
8.8
B7
8.8
B7
8.8
B7
8.8
B7
Sulfur (% max)
Elongation (%
min)
Tensile strength
(N/mm² min)
Yield strength
(N/mm² min)
Tolerance
0,150,40
0,370,49
0,025
0,040
12
16
860
830
660
720
Note
Just an overlap of 0,03 %
Updated requirement for
8.8 in 2009.
PED have a minimum
requirement of 14 %.
No steel mill will be willing or able to control the parameters in order to
produce steel only within these two grades overlapping values.
One solution would be that PED and ASME jointly determine which
material to be allowed incorporated in the pressure vessel. But to reach
this might be a long journey.
Until then should the pressure vessel manufacturer follow the rules and
directives that are valid and not invent their own interpretations and
requirements.
Motorgatan 2 | SE 442 40 Kungälv |Telephone: +46 (0) 303-24 34 40 | Fax: 0303-24 50 15 |info@appro.se | www.appro.se
The most important reason why to follow these directives is the safety
issue. So by using unclear or even false specifications, then you create
possibilities for hesitant screw manufacturers and wholesalers to market
and sell products that do not meet the real requirements.
These products can cause serious injury or risk of fatalities when they are
subjected to pressure and forces that they cannot handle. Last but not
least, you must also take into account the costs that such accidents or
production break downs will cause.
Motorgatan 2 | SE 442 40 Kungälv |Telephone: +46 (0) 303-24 34 40 | Fax: 0303-24 50 15 |info@appro.se | www.appro.se