The Hose Selection Guide: Under pressure

Do you know what role pressure plays when choosing a new hose? 

The pressure in a hose is crucial to both its performance and safety. It is important to understand the difference between working pressure and burst pressure, and how they affect the hose’s durability and service life. And then there’s the matter of temperature... 

Wouldn’t it be nice to have a transparent understanding of these concepts, so you can make better choices and improve both the efficiency and safety of your process plant? 

Read on in this edition of the Hose Selection Guide, where we focus on the role of pressure in hose selection and how temperature also comes into play. 

When we talk about hoses for industrial use, there are two concepts you need to be aware of: working pressure and burst pressure. 

• Working pressure is the maximum pressure a hose can safely and effectively handle under normal operating conditions. 
• Burst pressure is the point at which the hose can no longer withstand the pressure and will fail. 

It’s important to understand these concepts to ensure you select the right hose for your needs and maintain safe and efficient operation. If the hose does not meet the requirements, your production risks coming to a complete standstill. In the worst case, this can result in life-threatening injury, particularly in connection with CIP cleaning, which often involves high-temperature chemical liquids. 

Temperature has a decisive influence on a hose’s resistance to working pressure. 

As the temperature rises, the hose pressure often drops as a result. Consequently, the strength of the hose material is reduced and the hose becomes less resistant to working pressure. For example, if you have a hose rated at 10 bar at 20°C, the working pressure typically drops by 40% when the temperature reaches 90°C. However, this varies from hose type to hose type. 

It's essential to consider operating temperatures alongside pressure requirements when selecting the most suitable hose. Ensure it can withstand both the necessary working pressures and the expected operating temperatures. 

NB! Pressure specifications for a hose are always stated at a temperature of +20°C, for example as shown below. 

Pressure testing is essentially your extra assurance that the hose can withstand the working pressure you plan to use in the system. It's a controlled strength and leak test in which the hose is subjected to a brief static overpressure to confirm its full integrity before it goes into service. 

The aim is to identify weaknesses in either the hose or the assembly of the couplings before you put it into operation. In this way, you reduce the risk of bursts and leaks, which could otherwise lead to personal injury, production stoppages or, in the worst case, product recalls. 

Hose failures rarely manifest as a sudden and ‘clean’ burst without warning. Often, a rupture is the culmination of a prolonged degradation process. Repeated overpressure or the dreaded pressure surges (hydraulic shocks) put the hose’s internal structure under severe strain, leaving tell-tale signs that you can nip in the bud. 

It's important to recognise the visual indicators before they develop into an actual failure during operation. Here are the most common signs that your hose is at risk: 

• Bubbles in the outer tube: It's one of the most critical signs. It often indicates that the fluid or gas has penetrated the hose wall and is now accumulating beneath the outer jacket. If the ‘bubble’ bursts, it can result in a dangerous jet of fluid under high pressure. 
• Micro-cracks and ‘weather checking’: Small cracks in the surface indicate that the material has lost its elasticity (often due to heat or UV light). This can allow moisture and the fluid to reach the reinforcement if the cracks penetrate the cover. 
• Moisture or fluid in the reinforcement: If you see liquid seeping out at the reinforcement itself or at the transition to the coupling, it's a sign of corrosion of the steel reinforcement, which rapidly weakens the hose's fundamental strength. 
• Bulges and deformation: Localised ‘bulges’ on the hose or signs that the hose is starting to move out of the coupling’s crimp are direct warnings that the reinforcement has failed. 

Regular inspection and replacement according to a fixed schedule, combined with pressure testing of critical hose joints, is therefore a central part of a preventive maintenance strategy. Ultimately, it is a matter of common sense and economics: it's often far cheaper to replace a hose “too early” than to deal with the consequences of a rupture under full high pressure. 

For us, pressure is not a theoretical concept, but part of our standard quality assurance procedure. We pressure-test hoses with a safety margin of typically 1.5 times the specified working pressure, so there is documentation that the solution can withstand the real-world conditions at your plant. This means that if your working pressure is 10 bar, we typically pressure-test at 15 bar. 

If the hose is used in critical process lines or audits, you may wish to opt for a pressure test certificate alongside your hose solution. The certificate documents, amongst other things, customer data, hose specifications, test standards used (ISO 1307 and DIN 7715), as well as test pressure and inspection date. 

This makes it easy for you to document to authorities and internal quality departments that the hose has been tested and approved for your specific operating conditions. 

Did you catch Peter’s Week featuring the hose pressure test? We’ll show you how we pressure-test hoses. This gives you an insight into how we work with pressure and safety in practice. 

In the next edition, we’ll take a closer look at hose coupling types and examine their specific properties. We’ll give you a simple overview and equip you even better to make the right hose choice!