3.9 GHz Flash Cryostat -- Pressure Vessel Spec

Bernd Petersen DESY-MKS

May 7,2007

1.General:

Fermi National Accelerator Laboratory (FNAL) will manufacture a 3.9 GHz
Cryostat in the framework of a collaboration contract with DESY (see
email and note from Helen Edwards dated April 25,2007.) The 3.9 GHz
Cryostat will be installed in the FLASH-linac at DESY Hamburg.

The 3.9 GHz FLASH cryostat has to conform to the European legal
regulations. DESY will be the importer into the European Union and has
to certificate the conformity to the European regulations.

As part of the cryogenic installations of the FLASH-linac (former
TTF2-linac) the 3.9 GHz cryostat will be treated according to the TTF2
risk analysis (Gefahrenanalyse nach Anhang I der
[D]{.underline}ruck[g]{.underline}eräte[r]{.underline}icht[l]{.underline}inie
DGRL, May 8, 2003). With reference to this analysis, the cryogenic
equipment of the 3.9 GHz crystat will be assessed to fall below module I
of the DGRL, as a consequence the cryogenic installations require no
authorized third party inspections.

According to our risk analysis, the 3.9 GHz cryostat shall be treated in
line with the standard 1.3 GHz cryomodules: the niobium material of the
cavities can not be certified for the use at low temperatures. The
thermal shields and the vacuum vessel of the cryostat act as containment
for the inner 2K pressure vessel (see also DESY note D5/591, December 1,
1993.)

The DESY safety rules are fulfilled as soon as the cryostat is
conforming to the EU rules.

2\. Technical rules

The design and construction of the 3.9 GHz cryostat has to be conforming
to the DGRL. According to the DGRL, the manufacturer has to take the
responsibility for the application of suited technical rules, which are
not defined in detail in the DGRL. In case of the 3.9 GHz cryostat, DESY
as the importer takes action for the manufacturer outside the EU.

At DESY we apply the AD2000 technical rules or the European harmonized
rules. **[But according to our risk analysis also the US ASME
regulations for pressure vessels can be applied]{.underline}.** This is
underlined by the fact that since a decade, we have already cryogenic
components in use at TTF and FLASH, which were designed and constructed
according to ASME regulations (FLASH feed box, test cryostats).

2.1 Choice of materials for low temperature use

The choice of materials for use at low temperatures must accord to the
European harmonized rules (see attachmentA1). [If you will use the
austenitic stainless steels 316L (1.4435 DIN EN 13445-2) or 316LN
(1.4429) you should be perfectly in line not only with the EU rules but
also with ASME.]{.underline}

On default, materials may be used, which are allowed by the ASME rules
for pressure vessels at low temperatures (but steel 321 must be
avoided!). For the Ti-vessel we use titanium DIN/EN 3.7035, this
corresponds to Ti grade 2.

According to the DGRL there is no way to certify niobium for the use at
low temperatures.

All 'pressure vessel parts' -- all parts of the 2K, 4.5K and 40/80K
circuits (apart from niobium)- require material certificates. (On
default, the content and quality of the certificates should correspond
to the ASME code for pressure vessels and use at low temperatures.)

The weld additives used for the pressure vessel parts shall correspond
to the ASME code (or related rules), shall be suited for low
temperatures and need material certificates.

3\. Pressure vessel spec

Apart from the cavity made from niobium, all parts of the 3.9 GHz
cryostat shall be designed and manufactured in accordance to the ASME
pressure vessel code for the use at low temperatures.

3.1 Spec of cryogenic circuits

3.1.1 40-80K shield circuit

Design temperature: 40K ; design pressure: 20 bar abs

2.  4.5K shield circuit

Design temperature: 4K; design pressure: 20 bar abs

3.  2K circuit

design temperature: 2K; design pressure (\*): 2 bar abs

(\*) at room temperature an outer pressure not higher than 2 bar abs
(cavity under vacuum) can be applied to the cavities. As a consequence,
all safety valves of the 2K circuit of FLASH are set to an opening
pressure of less than 2 bar abs. At cold the cavities may tolerate
pressures up to 4 bar abs. Therefore it is recommended to design all
parts of the 2K circuit -- apart from the cavities -- to a pressure of 4
bar abs, if possible.

4\. Standards & Procedures

All standards and procedures according to the ASME pressure vessel code
(including test procedures) shall be applied. In particular:

4.1 Complete certification for all pressure vessel materials is
required.

4.2 All welding procedures have to be supervised and documented.

4.3 All test procedures, in particular pressure tests, have to be
documented.

4.4 A complete technical documentation has to be delivered (technical
drawings, engineering docs etc.)

4.5 An operation description is required.

A 1)

European Harmonized Rules

Stainless steels for the use at low temperatures

**DIN EN 13445-2**

**B.2.2.4 Lowest material temperature for austenitic stainless steels**

**Apply also for 2K !**

**Tabelle B.2-2---Niedrigste Werkstofftemperatur T~M~ nichtrostender
austenitischer Stähle**

**(material spec corresponding to ASTM type AISI may differ ! On default
apply ASME spec)**

+-------------------+-----------+------------------+------------------+
| **Material spec** | **DIN EN  | **ASTM type**    | **T~M~ (in °C)** |
|                   | number**  |                  |                  |
|                   |           | **AISI**         |                  |
+-------------------+-----------+------------------+------------------+
| **X1NiCrMoCu      | *         |                  | **-270**         |
| 31-27-4**         | *1.4563** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X1CrNiMoN       | *         |                  |                  |
| 25-22-2**         | *1.4466** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X1CrNi 25-21**  | *         | **310 L**        |                  |
|                   | *1.4335** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X2CrNiMoN       | *         | **316 LN**       |                  |
| 17-13-3**         | *1.4429** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X2CrNiMoN       | *         |                  |                  |
| 17-11-2**         | *1.4406** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X2CrNiMoN       | *         |                  |                  |
| 18-12-4**         | *1.4434** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X2CrNiMo        | *         | **317 L**        |                  |
| 18-15-4**         | *1.4438** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X2CrNiN 18-10** | *         | **304 LN**       |                  |
|                   | *1.4311** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X2CrNiMo        | *         | **316 L**        |                  |
| 18-14-3**         | *1.4435** |                  |                  |
+-------------------+-----------+------------------+------------------+
| **X2CrNi 19-11**  | *         | **304 L**        |                  |
|                   | *1.4306** |                  |                  |
+-------------------+-----------+------------------+------------------+
|                   |           |                  |                  |
+-------------------+-----------+------------------+------------------+
|                   |           |                  |                  |
+-------------------+-----------+------------------+------------------+
|                   |           |                  |                  |
+-------------------+-----------+------------------+------------------+
|                   |           |                  |                  |
+-------------------+-----------+------------------+------------------+
|                   |           |                  |                  |
+-------------------+-----------+------------------+------------------+