Concrete Pipe Gaskets

Design

Design entails the selection of material, joint configuration and gasket profile.

Materials

Numerous rubber compounds are available for gaskets. Selection of the appropriate material depends on the desired physical properties and chemical resistance needed for the specific application. The following rubber compounds are standard materials for gasket extrusion. Special compounds are also available upon request:

Polyisoprene — Similar properties to natural rubber. Low cost; 1.0-3.5 ksi tensile strength; 300-750% elongation; (-)60-180°F temperature range; excellent compression set and rebound rating; excellent cracking, tear, abrasion, water, acid and impact resistance.
Neoprene (chloroprene) — Very good ozone, cracking and sunlight resistance; 0.5-2.5 ksi tensile strength; 100-800% elongation; (-)80-300°F temperature range; excellent flame, abrasion, impact, oxidation and acid resistance; good water, petroleum and hydrocarbon oil resistance.
Nitrile — Nitrite - Excellent water, tear, abrasion, hydrocarbon oil and petroleum resistance; 1.0-2.5 ksi tensile strength; 400-650% elongation; (-)40-300°F temperature range; excellent compression set.
EPDM (ethylene-propylene) - Excellent weather, sunlight, ozone, oxidation, water, acid, alkalis, esters, and abrasion resistance; 0.3-2.5 ksi tensile strength; 100-700% elongation; (-)75-400°F temperature range.

Joint Configuration

Each gasket is customized to the joint configuration provided by the pipe supplier. As a minimum, the following dimensional information must be supplied for this evaluation and design:

O-Ring Joint

Single Offset Joint

Gasket Profile

Each gasket profile is analyzed for its overall performance with regard to the specified joint configuration. This evaluation entails determination of the nominal, minimum and maximum joint opening and the respective deformations at these locations. Each gasket is then tested at our research laboratory and the resulting forces at these deformations provided as a force-deformation curve. These forces are then evaluated for minimum sealing force and maximum bell force to prevent leaking or bell cracking.

Sample Force vs Defamation Curve

Drawings of eleven different profiles

Sample Available Profiles
(Custom Designs Available Upon Request)

Performance

All concrete pipe profile gaskets are designed to meet the physical requirements of ASTM C 443, "Standard Specification for Joints for Circular Concrete Sewer and Culvert Pipe, Using Rubber Gaskets." Concrete O-ring gaskets meet the physical requirements of ASTM C 361, "Standard Specification for Reinforced Concrete Low-Head Pressure Pipe." In addition to the physical property tests required for the rubber, each standard also includes optional plant hydrostatic testing to 13 psi for C443 pipe and up to 120% of the internal working pressure for C361 pipe.

Field testing is performed to the pressures indicated in the local project requirements. Testing is accomplished in accordance with the respective ASTM standards covering vacuum (negative air pressure), air or hydrostatic testing. As a minimum, all concrete pipe gaskets will meet or exceed field test pressures of 13 psi. Gaskets with ratings greater than 13 psi can be designed upon request.

Testing

As a minimum, each gasket is tested and certified to the following requirements:

Physical Requirements for Elastomeric Seals for Concrete Pipe
Tests	Limits	Units
Tensile Strength, minimum	1200	psi
Elongation, minimum	350	%
Hardness, Type A durometer	30 to 70	durometer
Low-Temperature Hardness (max. increase)	15	durometer
Compression Set, maximum	25	%
Ozone Resistance	no cracks
Accelerated Aging:
Tensile Strength, max. decrease	15	%
Elongation, max. decrease	20	%
Hardness, max. increase	8	durometer
After Water Immersion:
Volume, max. increase	5	%

Additional physical requirements for specialty compounds can be provided for review and approval.