Petrochemicals and refining
ANSI flanges · process lines
Flanges in high-pressure, high-temperature process lines. Typical combination: spiral-wound gasket + Inconel 718 Belleville on critical bolts.
Flange
washers
Leak prevention in flanged joints exposed to thermal cycling, vibration or gasket relaxation.
Temperature range
−350 °C → +650 °C
Materials
17-7 PH · Inconel 718 · H-13
Engineering support
In-house technical team since 1975
01
What is a flange washer
A flange washer —also called a pressure disc spring, disc spring or coned-disc washer— is a conical elastic component fitted under the nut or bolt head in a flanged joint to maintain a constant axial load on the gasket.
Unlike flat washers, its frustoconical geometry stores elastic energy that compensates for the loss of preload caused by:
- Bolt relaxation (creep / stress relaxation) at service temperature.
- Differential thermal expansion between flange, bolt and gasket — different expansion coefficients.
- Embedment and creep of the sealing gasket material.
- Vibration and dynamic loads that tend to loosen the connection.
These washers are referenced by the stud diameter in inches, with three force levels for each. They can also be supplied for stud diameters in the metric system. Contact us about your case.
PHOTO + DIAGRAM · flange assembly with a Belleville under each nutBelleville washers → marked in red
02
When to use
Installing Belleville washers on flanges is justified when the joint is exposed to any of the following scenarios. The washer acts as a load reserve: when the gasket or the bolt loses effective length, the washer expands without recovering its full height, allowing the joint to stay sealed (with a lower force, but enough to prevent leaks).
01
Thermal collapse · thermal shock
During a thermal cycle, in a flanged joint, the bolt/stud, the flange body and the gasket change at different rates. Flange washers, pre-compressed to the tightening torque required by the gasket, absorb these changes so that the joint never loses its clamping force, thereby preventing an unwanted leak.
02
Mechanical collapse
Fully rigid, 100% contact causes two opposite modes: load loss from gasket settling, or excessive values that break bolts or gaskets. The elasticity of the flange washer absorbs these stresses and keeps the force within the operating range.
03
Bolt relaxation · creep
Over time and at service temperature, the stud tends to deform/elongate because it is under tension. This elongation is absorbed by the flange washers, so that the joint does not lose its contact force, preventing leakage of the fluid running through the pipe. (The elongation of the stud is smaller than the elongation of the flange washer.)
04
Electrical connections · Joule effect
Electrical connections are often made up of materials with different coefficients of thermal expansion. In addition, the joint materials carry more current than the bolts, which causes the joint to heat up more than the bolts do. The resulting differential thermal expansion increases the load on the bolt, which can lead to creep in the joint components. Introducing spring washers reduces this detrimental effect.
↘ Typical configuration: a pair of Belleville washers under each nut of the electrical terminal, usually in 17-7 PH or Inconel 718 depending on the service temperature.
PHOTO · flanged electrical connection · sectionwashers in red
Terminals connected by a through-bolt flange. The Belleville washers absorb the cyclic expansion from the Joule effect and maintain the contact pressure between surfaces.
— Functional summary
Flange washers protect flanged joints against leaks, giving them the elasticity each case requires.
03
Materials · three alloys for three ranges
Surisa manufactures flange washers in three materials that cover virtually every industrial application. The choice depends on the service temperature, the working atmosphere (corrosion) and the frequency of thermal cycling.
17-7 PH
X7CrNiAl17-7 · 1.4568
−200 → +300 °C
Corrosion resistance
Good (precipitation semi-austenitic)
Mechanical
High strength-to-weight ratio. Retains its elastic properties at moderate temperature and behaves stably in cryogenic service.
Application
Flanges in the chemical industry, electrical connections, moderately corrosive environments, cryogenic equipment down to −200 °C.
Inconel 718
NiCr19NbMo · 2.4668
−250 → +600 °C
Corrosion resistance
Excellent · oxidation and severe chemical attack
Mechanical
Creep resistance and thermal-fatigue resistance thanks to γ″ precipitation (Ni₃Nb). Retains its yield strength at high temperature.
Application
Petrochemicals, steam generation, turbines, exhaust systems, chemical plants with aggressive fluids.
H-13
X40CrMoV5-1 · 1.2344
−100 → +590 °C
Corrosion resistance
Limited · not stainless. Accepts surface treatment for outdoor use.
Mechanical
Cr 5 % hot-work steel. Hardness retained at elevated temperatures. Excellent thermal-fatigue behaviour.
Application
Flanges in high-temperature process lines without corrosive agents. Applications with intense thermal cycling.
The ranges are indicative for preliminary design. The admissible service temperature also depends on the load, the frequency of thermal cycling and the atmosphere.
Let's talk about your project
Tell us about your use case and our engineering team will help you choose the optimal solution.
04
Thermal range · -350 °C → +650 °C
All three materials overlap in the central range of conventional service. The critical difference lies at the extremes: cryogenics at the bottom, high-temperature creep at the top.
Inconel 718 is the only material suitable for continuous service above 550 °C, thanks to its γ″ precipitation. 17-7 PH is the default choice when there is moderate corrosion or cryogenic service. H-13 covers the middle ground in non-corrosive applications where thermal cycling is intense.
For the upper limit of the range by material, we recommend validation with a specific relaxation calculation at the actual service temperature.
FIG · service temperature ranges by material
05
Applications · sectors where they are critical
Flange washers are the standard when a gasket leak has critical consequences (safety, plant shutdown, electrical inefficiency) and the environment makes the loss of initial preload inevitable.
Power generation
Steam · combined cycle
Heat exchangers, turbines and superheated-steam piping where thermal cycling is continuous and gasket failure has critical impact.
Chemical industry
Corrosive environments
Plants with aggressive fluids where stainless steel or a nickel alloy is mandatory. 17-7 PH for moderate corrosion, Inconel 718 for severe environments.
Power electrical connections
Substations · transformers
Flanged connections in industrial switchgear, transformers and substations. The Belleville absorbs the cyclic expansion from the Joule effect and prevents hot spots.
Cryogenics
LNG · air separation · liquid H₂
Equipment down to −250 °C where 17-7 PH stainless steel and Inconel 718 maintain stable elastic behavior. Critical in LNG and liquid hydrogen plants.
Industrial valves and gaskets
Dynamic sealing · flange closure
Flanged closures on valves with a stem, where leakage is a direct function of maintaining the preload on the gasket assembly.
06
How to determine the tightening torque
The tightening torque in a flanged joint with Belleville washers is not a catalogue value: it depends on several coupled factors that must be assessed together.
The main factors are: bolt diameter and grade, thread-nut friction coefficient (a function of the lubricant and coating), closing load required by the gasket and the load-deflection curve of the selected washer.
The usual procedure is: (1) define the clamping load required on the gasket, (2) select the Belleville washer whose F-s curve delivers that load within its elastic working zone, (3) calculate the bolt torque needed to reach the total preload with the actual friction coefficient.
07
Frequently asked questions
01 What is the difference between a DIN 6796 Belleville washer and a flange washer?
DIN 6796 washers are standardized conical spring lock washers for structural bolting, designed to prevent loosening of bolted joints and to work almost flat, and are single-use. Flange washers are pressure disc springs designed to maintain a significant elastic preload throughout the life of the joint, with a load-deflection curve calculated to compensate for thermal and mechanical relaxation. The former are an anti-loosening safety element; the latter are an active load-maintenance element (live loading).
02 Up to what temperature can I use a flange washer?
It depends on the material. 17-7 PH stainless steel maintains stable elastic properties from −200 °C up to about +300 °C. Inconel 718 is the choice for continuous service up to about +600 °C thanks to its creep resistance, and goes down to −250 °C. H-13 covers the intermediate range in non-corrosive applications, from −100 °C up to about +590 °C. For service at the limit of the thermal range we recommend validation with a specific calculation.
03 Can I replace a spiral-wound gasket with flange washers?
No: they are complementary elements, not alternatives. The gasket remains the primary sealing element. Belleville washers are fitted under the bolt nut to maintain the preload on that gasket when the system undergoes thermal cycling, vibration or relaxation. The combined installation (spiral-wound gasket + Belleville washers on the bolts) is common in critical petrochemical and power-generation flanges.
04 How many Belleville washers are fitted per bolt?
In a flanged joint, the usual practice is to fit two washers, one under each nut; these washers are not stacked in stacks. Surisa's calculation program is exclusive to DIN 2093 disc springs and does not apply to flange washers. To size a specific joint, send us the joint data (flange standard, bolt, temperature and gasket) and our technical team will advise you on the right material and arrangement.
05 Does Surisa manufacture special sizes or only catalogue items?
The vast majority of the applications we receive are solved with catalog washers; it is rare to have to manufacture sizes outside the catalog, unlike what happens with DIN 2093 disc springs. Occasionally, special versions can be manufactured on request.
The usual lead time for standard references is 72 to 96 hours: the material is imported from the United States, so transit and customs procedures may extend that time. Confirm your reference and we will indicate the actual lead time in each case.
06 What is the difference from the DIN 2093?
The DIN 2093 is a general-purpose elastic element: it is designed for a specific force and deflection. The flange washer is a preload-maintenance element: it is designed to compensate for load loss in the flange bolt due to relaxation and temperature.
Dimensionally they are also different, both in the ratio between external diameter and internal diameter and in the ratio between deflection capacity and free height.
Let's talk about your project
Tell us about your use case and our engineering team will help you choose the optimal solution.