Regarding specifications and management guidelines

Flexible joints

Editorial supervision by Government Buildings Department, Minister’s Secretariat, Ministry of Land, Infrastructure, Transport and Tourism

“Machinery and Equipment Work Supervision Guidelines,” 2019 edition

These are to be synthetic rubber, with a steel flange and reinforcing materials included, with sufficient flexibility, weatherability, heat resistance, and pressure resistance. Its overall length shall be as follows

  • (a) The nominal diameter of 40 or less shall be 300mm or less.
  • (b) The nominal diameter of 50 or 80 or less shall be 500mm or more.
  • (c) The nominal diameter of 100 or more shall be 700mm or more.

TOZEN conforming products (cylinder type)


(Products conforming with public construction work standards specifications)



Joints to absorb displacement used in earthquake‐resistance measures related to tanks etc. are typically called flexible joints.
The name used in the “Machinery and Equipment Work Shared Specifications” was changed in 1989 edition from the previously-used native Japanese word “katō tsugite” to the English loan word “furekishiburu jointo.”

Editorial supervision by Government Buildings Department, Minister’s Secretariat, Ministry of Land, Infrastructure, Transport and Tourism
“Machinery and Equipment Work Supervision Guidelines,” 2019 edition
2.2.9 Flexible joints p.165~170

Table 2.2.6 Types of pipe joints

Based on SHSSE-S 008: 2008

Types Categories Fluid
connection shape
working pressure(MPa)
Cylindrical pipe joint Category A Cold water
Warm water
Cooling water
Heat source water
Water supply
Flange shape 0~60 0.5※、1 or 2 20~600 Integral multiple of 50
Category B 0~70 20~300 Integral multiple of 50
Sphere type pipe joint Category B Manufacturer specifications
Bellows type pipe joint
Flange shape
Screw shape

0.5MPa is compatible with drainage systems

Table 2.2.7 Types of pipe joints

Based on SHASE-S 008:2008

Categories Maximum perpendicular
displacement amount[mm]
usage Purposes
Category A 100or more Earthquake‐resistant
Mainly absorbing sudden
and large displacement due to earthquakes
Type designed to cope with ground subsidence Mainly absorbing displacement due to ground subsidence
at building entry points where there is a risk of subsidence
For seismic isolation Mainly the absorption of displacement between seismically
isolated buildings and the ground
Category B Less than 100 Protecting equipment and
tanks in earthquakes
Follow the displacement of the piping around equipment
like a pump or water tank by earthquake
or on-off operation of the equipment.

(C)Synthetic rubber material(For water)

In the “Standards Specifications,” rubber displacement absorption pipe joints for use with water are specified as having a steel flange. In the SHASE-S 008: 2008 specifications (rubber displacement absorption pipe joints), pipe joints are divided into Category A and Category B based on the types and face‐to‐face dimensions shown in Table 2.2.6 and the range of maximum perpendicular displacement amounts shown in Table 2.2.7. The “Standards Specifications” show overall lengths for synthetic rubber flexible joints envisaging typical applications.

In addition, joints used in drinking water pipes shall present no hygiene issues nor adversely affect water quality.
It is preferable that EPDM with strengthened chlorine resistance is used on the rubber materials coming into contact with fluids in synthetic rubber flexible joints used in water supply systems where the residual chlorine concentration is high. (from Guidelines)
In recent years, direct water supply systems (high residual chlorine concentration) have come to be used in typical buildings, and the chlorine concentration in tap water has also further increased.

Rubber degradation occurs due to the oxidative effect of oxygen in the air and dissolved in fluids. This effect is significantly reinforced by heat, residual chlorine, copper, and salts such as manganese. This oxidative effect causes the rubber surface to become brittle, and rubber to peel away due to liquid flow, vibration, etc.

〈Our interpretation of categories〉

Products are divided into 2 categories based on the displacement amount, being Category A (100mm or more) and Category B (less than 100mm). It is possible that Category B also includes products between short surfaces compliant with standards specifications, but as the application is “protecting equipment and tanks in earthquakes” and the purpose is “…absorbing displacement… due to equipment starting and stopping as well as piping displacement due to earthquakes,” the main application and purpose is therefore absorbing displacement. A common-sense interpretation is thus that the Category B range will broadly cover products of 50mm or more and less than 100mm.

(Citing Asyu A1 of HASS 008-1999/HASS = current SHASE-S)

Products conforming with guidelines (bellows type)