DN100 (4") metal expansion bellows — axial movement, EJMA build, UK stock
What the UKGP-MEB-04 DN100 (4") metal expansion bellows does
The UKGP-MEB-04 is a DN100 (4") multi-ply 321 stainless steel metal expansion bellows (also called a metallic expansion joint or stainless bellows compensator) built to EJMA Section 4. It absorbs axial thermal growth in high-temperature steam, hot oil, flue-gas and process pipework where elastomer rubber bellows cannot survive the operating temperature. The bellows convolutions deform elastically to accept up to 50 mm of axial movement plus 10 mm of lateral offset, allowing rigid steel pipework to grow and contract without transmitting axial load into pumps, vessels and connected equipment.
Why specify a metal expansion bellows for steam, hot oil and exhaust
Above roughly 110 °C an EPDM rubber bellows is out of spec — the elastomer hardens, the bond to the flange ring fails, and the joint leaks. A stainless steel metal expansion bellows like the UKGP-MEB-04 works to 550 °C continuously and 800 °C peak in the 321 grade, making it the only realistic choice for LP/MP/HP steam mains, hot-oil thermal-fluid loops, flue-gas ducting, dryer manifolds and turbine bleed lines. The single-ply equivalents you see in low-cost imports cycle-fatigue in months on real-world steam duty; multi-ply construction puts three thinner plies in parallel so each ply takes less strain per cycle, which is what delivers the 20+ year service life the EJMA standard targets.
Movement capacity, anchors and tie-rod restraint
The UKGP-MEB-04 DN100 (4") metal expansion bellows is an axial joint — it must be installed between two anchored points so the pipework forces the bellows to compress and extend rather than letting line pressure pull it apart. Pressure thrust on a DN100 bellows at 16 barg is around 13 kN; without main anchors, that load tears the convolutions off the tangent. Where main anchors aren't feasible, specify the tied-lateral or universal variant instead, or order the UKGP-MEB-04 with our factory-fitted tie-bar restraint kit. Always size at no more than 75 % of rated movement to leave headroom for installation tolerance and over-temperature events.
Metal vs rubber expansion bellows — when to pick which
Rubber bellows are quieter, cheaper and unbeatable for pump-vibration isolation on water systems below 100 °C. Metal expansion bellows are the right call above 110 °C, for steam, hot oil, flue-gas and chemical service, and wherever ozone, UV or hydrocarbon exposure rules out elastomers. For a side-by-side comparison see our rubber vs metal expansion joints guide linked below.
Standards: EJMA, PED and CE marking
Every UKGP metal expansion bellows is built to the Expansion Joint Manufacturers' Association (EJMA) Section 4 design rules, hydrostatically tested at 1.5 × design pressure and supplied with a signed certificate of conformity. Bellows above DN50 / above 0.5 barg fall under PED 2014/68/EU and are CE marked. Material certificates (EN 10204 3.1) on the 321 / 316L plies are available as a no-cost option — specify at order.
Price, lead time and ordering the UKGP-MEB-04
The UKGP-MEB-04 DN100 (4") metal expansion bellows is £545 ex VAT, in UK stock for same-day dispatch on orders placed before 3 pm Mon–Fri. Specials — Inconel 625, PN25/PN40, weld-end terminations, hinged or universal arrangements — are quoted inside one working day.