Rule of thumb · applies
Gas only with the version approved for it – why the same compression fitting may carry gas outside and not inside
Gas only with the version approved for it – inside buildings that means HTB.
A rule of thumb replaces neither the design calculation nor the applicable standard.
- Category
- robust rule
- Standards referenced
- DIN 3387-1 (compression fittings for gas), DVGW G 260 (gas quality), DVGW G 600 / TRGI (domestic gas installation, HTB requirement) – manufacturer data Gebo (series 150/220, 180/225 HTB) and GF (PRIMOFIT, FIREJOINT)
Rule of thumb
A malleable-iron compression fitting with NBR seal may carry gas outside buildings (DIN 3387-1, up to 5 bar); inside buildings the joint needs the higher-thermal-resistance version with a fire-resistant graphite seal ring – at Gebo the series 180/225, at GF the FIREJOINT. Repair bands may carry gas only outside and only with NBR.
Where does the rule come from?
The rule comes from domestic gas installation in Germany: components in buildings must stay tight for half an hour up to 650 °C in case of fire (HTB requirement of the TRGI) so that no gas escapes while the fire brigade works. An NBR seal melts before that. The HTB fitting therefore carries, in addition to the O-ring, a graphite seal ring that takes over once the rubber is gone – and that is why the approval (DVGW register number) stands in the catalogue next to every series.
What is technically correct?
Three questions before every gas fitting: Where is the line – outside (service line, buried) or inside the building? Which pressure – Gebo HTB and standard up to 5 bar, GF PRIMOFIT up to 10 bar outside, FIREJOINT 5 bar inside? Which pipe – threaded pipe to EN 10255, PE pipe (Gebo 153/156 for service lines)? Only the approval in the catalogue (“gas: DIN 3387-1, DVGW reg. no. …”) makes the fitting a gas part; the boiler-tube series (15S/22S) and the brass series (313/314) name no gas at all – they are none.
Where does the rule end?
- LPG, hydrogen: GF names natural gas, LPG and hydrogen up to 20 percent by volume for PRIMOFIT; Gebo names gases to DVGW G 260. Beyond these data: ask the manufacturer.
- Malleable-iron repair clamps (type DS) are water parts – the catalogue names no release for gas.
- The rule says which part; who may install it and how the line is tested is told by the TRGI – that is the business of the licensed installer.
What does the standard say?
DIN 3387-1 regulates detachable pipe joints for gas lines (metal-sealing or with elastomer) and is the test basis of the DVGW approval; the TRGI (DVGW G 600) demands the higher thermal resistance for the pipework inside the building. We reproduce the numbers as the manufacturers print them – we have not bought the standard texts themselves.
DIN/EN versus ASME/ASTM
In the ASME world there is no HTB logic of this form; gas distribution in buildings follows the national codes (NFPA 54 in the USA), and mechanical fittings need a listing per application there. Transferability is nil – a DVGW-tested HTB fitting is nothing in the USA without a listing, and vice versa.
Worked example
A 1 inch gas service line lies in the front garden, the line continues through the basement wall to the meter. Outside: Gebo series 150 type A, gas up to 5 bar, DIN 3387-1. Inside, between house entry and main shut-off: series 180 (HTB). Same dimension 33.7 mm, same thread, different seal, different approval – and two different article numbers.
Zickwolff reference
From daily business: the HTB fittings are listed with us, not stocked – whoever repairs the gas line inside a building best tells us so in the inquiry, then we clarify the version before a standard part reaches the site.
Checked today
Verdict: applies (class A). The rule follows the catalogue releases and the TRGI requirement; it is neither installation instructions nor legal information.
Further reading
- Compression fittings for steel pipe and boiler tube: Gebo malleable iron, brass, HTB for gas, GF PRIMOFIT – Compression fittings for steel pipe and boiler tube, HTB version
- Compression fittings for PE, PP and PVC-C pipe and the transition from steel to plastic – Compression fittings for PE pipe and steel-PE transition
- Repair clamps, stainless repair bands and tapping clamps: holes, cracks and later branches without welding – Repair bands for gas outside buildings
- FAQ on joining without welding: compression fittings, repair clamps, Multigebo in daily use – FAQ on joining without welding
- Seals and media: EPDM, HNBR, FKM, CIIR – which medium with which sealing ring – Sealing elements and media in press systems
- Seal before system – why the media list means the seal – Sealing element before system
Frequently asked questions
May I put a standard compression fitting on the gas line in the basement?
No – inside buildings the joint needs the HTB version (Gebo 180/225, GF FIREJOINT). The standard fitting is approved for gas outside only.
How do I recognise the HTB version?
By the type code with T (AT, OT, IT …) and by the approval in the catalogue; Gebo names the graphite seal ring and “650 °C / 30 minutes”.
May a stainless repair band repair a gas line?
Outside buildings with NBR seal up to 4 bar (middle) or per diameter table (maxi) – inside not.
Your inquiry to Zickwolff
Send us what you have – designation, standard, quantity, date. We will clarify the rest with you.
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Designation, standard and quantity are enough.
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