1. Environmental Impacts
The "economic life" of the regulator generally depends on mitigating the corrosive effects resulting from the combination of environmental factors through design and material selection. Therefore, a thorough understanding of environmental factors and their effects is essential.
Let's briefly discuss these effects in order and then explain how they can be eliminated through correct design and material selection.
Environmental impacts are mechanical, chemical, and thermal factors affecting the regulator. These factors often act as a combination, affecting both the inside and outside of the regulator. Therefore, here we will discuss the combined effects of these factors.
1.1. Mechanical Factors: Mechanical factors can be examined under three headings:
1.1.1. Effects of compressive forces
1.1.2. Effects of friction, wear, and fatigue
1.1.3. Loads at connection points.
1.1. 1. Pressure Factors
The pressures acting on the regulator can be examined in two separate groups:
a) Operating pressure/Inlet pressure; this is the pressure of the distribution network to which the regulator is connected. While this pressure varies seasonally, it is generally around 4 bar. Due to losses during operation or, preferably, a reduction in operating pressure, this pressure can drop to 0.5 bar. The effect of this pressure will be particularly noticeable on the SSV unit on the inlet side of the regulator. This area is directly exposed to the inlet pressure.
Our country is located in a region experiencing high seasonal temperature variations. Furthermore, in regions under the influence of a continental climate, the temperature difference between day and night is also very large. Due to this constantly changing thermal load, the screw threads in the aluminum body eventually fatigue and lose the torque provided by the initial tightening. As a natural consequence, leaks occur around the SSV cover of the regulators after a few years of use. This observation has been experienced for years in field applications, particularly by gas companies using SSV-type service regulators.
b) Network Accident Pressure; In regulators at stations supplying the gas distribution network, outlet pressures can rise for any reason, and if the SSV unit does not activate, there is a risk of a pressure of 15-20 bar entering the network. To ensure the regulator remains in a safe condition, a "withstand pressure" is defined in the TS10624 standard and other standards. While it varies depending on the service regulator body material, this pressure is approximately 16 bar.
Regulators containing plastic parts in the SSV unit and Stage 1 unit cannot withstand these high pressures for extended periods. They will cause both external and internal leaks, shortening the economic lifespan and hindering safe operation.
1.1.2. Effects of Friction, Wear, and Fatigue
The regulator is a device with constantly moving internal parts to maintain constant pressure depending on gas usage. Therefore, wear is natural as a result of the movement of these parts. The effect of wear leads to increased clearance in mechanical parts, and as a result, operating tolerances may change. An important parameter affecting "economic service life" is ensuring that the device operates within the tolerances required by standards throughout its service life. To ensure this, accelerated life tests should be performed on regulators. These tests simulate the regulator operating for 10 years and retest to determine if it remains within the standard tolerances. Another effect of wear is the potential for "internal leaks" in the regulator. This can lead to regulator malfunction and failure, or to its use at unsafe pressures. The most important issue to consider here is the condition of structures containing "movable O-rings" or "nutrings".
As you can see in the image above, the first stage shaft is sealed by a continuously moving O-ring. The volume of O-rings can increase or decrease by 30% due to the chemical effects of the gas. As a result, the moving O-rings in this area can lose volume due to chemical effects and wear down due to mechanical friction. Internal leaks resulting from this can lead to regulator failures and shorten its service life. The TS 10624 standard emphasizes that regulator parts must provide a seal even without lubrication.
2. Chemical Factors
Due to their operating environment, regulators are susceptible to corrosion from external factors such as water, humidity, ozone, cleaning chemicals, salt, etc. They are also exposed to internal corrosion due to the moisture, water, odorizing agents, and the chemical effects of the gas itself. Let's briefly look at the effects of this corrosion.
2.1. External Corrosion
Due to their operating environment, regulators can corrode on their external surfaces. The degree of corrosion can vary considerably depending on the location and operating conditions of the regulator. For example, humidity and salt can be very effective corrosion agents near the sea, rapidly eroding the regulator. On the other hand, products used in buried boxes can be directly exposed to water and even cleaning chemicals used on streets and roads. These corrosive agents have a higher impact, especially in the cover areas that close the first stages of the regulators. This is because the thickness of the cover area is much thinner than that of the housing. As shown in the image below, protecting regulators that contain pressure under the cover area against corrosion is of even greater importance. Because thinning and perforations in this area will directly lead to external leaks and even explosions.
Therefore, if there is pressure under the cover in regulators, the cover thickness should be kept high, taking this into consideration, or protected with measures such as paint against corrosion.
2.2. Internal Corrosion;
Due to the effect of the gas passing through them, corrosion and related wear can occur in the internal parts of the regulator, just as on the outside. These effects are particularly important for the parts involved in pressure regulation. The necessary precautions in this regard are explained in the materials section.
3. Thermal Factors
One of the most important factors affecting the economic life and "safe use" of the regulator is the operating ambient temperature and gas temperature. Due to the very different climatic conditions of our country, regulators can be exposed to ambient temperatures between -40 and +60 degrees Celsius.
Furthermore, in regions with a continental climate, these temperatures can frequently change significantly between day and night. As a result of this thermal effect, metal and plastic materials are constantly "working" and "fatiguing". Due to the effects of these fatigues, deformations in the high-pressure components of the regulator lead to external leaks. This is a common problem, especially after several years of seasonal changes.
On the other hand, especially at sub-zero temperatures, the freezing of water in the gas can cause "mechanism" lockups and jams, creating problems in terms of "safety" and "performance". Since the regulation process involves continuous movement, problems are generally not observed in the components involved in the regulation. However, the risk of components such as the static SSV unit becoming blocked due to water and cold and failing to activate when needed should be considered.