HG/T 20628-2009 English PDF (HGT20628-2009)

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HG/T 20628-2009: PTFE envelope gaskets for use with steel pipe flanges (Class designated)
HG/T 20628-2009
Chemical Industry Standard
of the People's Republic of China
HG
Replacing HG 20628-1997
PTFE Envelope Gaskets for use with Steel Pipe Flanges
(Class Designated)
(Class系列)
ISSUED ON. FEBRUARY 5, 2009
IMPLEMENTED ON. JULY 1, 2009
Issued by. Ministry of Industry and Information Technology of the People’s
Republic of China
[Including Corrigendum/Modification confirmed in May 2012. Text in RED]
Contents
1. Scope ... 3 
2. Normative references ... 3 
3. Gasket type and dimension ... 3 
4. Technical requirements ... 6 
5. Marking and Packaging ... 7 
1. Scope
This standard specifies the type, dimension, technical requirements and marking of
PTFE envelope gaskets for use with steel pipe flanges (Class designated).
This standard is applicable to the PTFE envelope gaskets for use with raised-face steel
pipe flanges that the nominal pressures are Class150 (PN20) and Class300 (PN50) and the
working temperature is less than or equal to 150℃ (specified in HG/T 20615).
Note. As for the use of the gaskets in which contain the material of asbestos, it shall meet the requirements of the relevant
laws and regulations. If the aforesaid gaskets are used, the protective measures shall be adopted to prevent man from damaging.
2. Normative references
The following provisions contained in the following standards are turned into the
provisions of this national standard by being referred in this national standard. For date
reference, the subsequent amendments to (excluding amending error in the text) or revisions
of, any of these publications do not apply. And parties to agreements based on this standard
are encouraged to investigate the possibility of applying the most recent editions of the
standards indicated below. For undated references, its latest edition referred to applies.
GB/T 3985 "Compressed asbestos fiber jointing"
GB/T 13404 "PTFE envelope gaskets for use with pipe flange"
HG/T 20615 "Steel Pipe Flange (Class Designated)"
HG/T 20635 "Specification for Selection of Steel Pipe Flange, Gaskets and Bolting
(Class designated)"
QB/T 3625 "PTFE Sheet"
QB/T 3626 "PTFE Steel Bar"
3. Gasket type and dimension
3.0.1 According to the processing method, the gasket type is classified into section type,
machine work type and fold type; and the types are expressed respectively with A type, B type
and C type (see Figure 3.0.1). A type and B type are applicable to the occasion that the
nominal dimension is less than or equal to DN500; and B type of the two is recommended. C
type is applicable to the occasion that the nominal dimension larger than or equal to DN350.
3.0.2 Gasket Dimension
1 Gasket dimensions of A type, B type and C type shall meet the requirements of Table
3.0.2-1 and Table 3.0.2-2.
2 The gasket thickness T in Table 3.0.2-1 and Table 3.0.2-2 is recommended thickness.
The other gasket thickness may be determined by the user, but it shall be indicated at the
Table 3.0.2-2 PTFE Envelope Gaskets Dimension (C type) (mm)
Nominal dimension
Coating inside
diameter Dl
Coating outside
diameter D3min
Outside diameter of the gasket D4
Gasket thickness
T DN NPS
Nominal pressure Class
350 14 356 412 449.5 484.5
400 16 406 469 513.0 538.5
450 18 457 528 548.0 595.5
500 20 508 578 605.0 653.0
600 24 610 679 716.5 774.0
Note. The gasket thickness T in the table is recommended thickness. The other gasket thickness may be determined by the
user, but it shall be indicated at the order time.
4. Technical requirements
4.0.1 PTFE coating material shall meet the requirements of FSB-2 which is specified in QB/T
3625 and the requirements of QB/T 3626.
4.0.2 Embedding layer or core material usually are paronite or non asbestos fiber rubber sheet.
If it is required by the user, the other proper material may be adopted, but it shall be indicated
in the order.
4.0.3 Dimension tolerance of gasket internal diameter D1 and outside diameter D4 shall meet
the requirements of Table 4.0.3. The tolerance of coating thickness is ±0.05mm and the
tolerance of gasket thickness is±0.25mm.
4.0.4 Coating surface shall be flat and smooth without buckling deformation and the thickness
shall be even. There shall be no such defects as pore and slag inclusion.
4.0.5 Compression ratio, rebound rate, stress relaxation ratio and sealing leak ratio of the
gasket shall meet the requirements of GB/T 13404.
Table 4.0.3 Dimension Tolerance of Inside Diameter D1 and Outside Diameter D4 of the Gasket (mm)
Nominal dimension ≤DN300 ≥DN350
Coating inside diameter D1 ±1.5 ±3.0
Outside diameter of the gasket D4
-1.5
-3.0
5. Marking and Packaging
5.0.1 The gasket shall be packaged respectively according to the type, specification and
material. There shall be production quality test conformity certificate at the delivery time. The
specified contents in Article 5.0.2 shall be indicated with label on the gasket.
5.0.2 Marking Illustration
Illustration 1. As for the machine-work-type PTFE envelope gasket in thickness (T) of
3mm for use with steel pipe flange that the nominal dimension is DN100 and the nominal
pressure is Class300, the core material is XB450 paronite; and the marking is.
HG/T 20628 PTFE envelope gasket (XB450) B 100-300
Illustration 2. As for the section-type PTFE envelope gaskets in the thickness (T) of
2.5mm for use with steel pipe flange that the nominal dimension is DN200 and the nominal
pressure is Classl50, materials of the embedding layer are chemigum sheet; and the marking
is.
HG/T 20628 PTFE envelope gasket (NBR) A 200-150
Illustration 3. As for the fold-type PTFE envelope gaskets in the thickness (T) of 4mm
for use with steel pipe flange that the nominal dimension is DN600 and the nominal pressure
is Classl50, materials of the embedding layer are non asbestos fiber rubber sheet; and the
marking is.
HG/T 20628 PTFE envelope gasket (AAA/BBB) C 600-150
Note. When the specific manufacturer (AAA) and grade (BBB) are selected by the user, the attaching label shall be marked
(AAA/BBB) on the gasket marks.