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Introduction

Inside the steam pipe, a small portion of steam will be compressed during the process of delivery. As a result, the image of steam condensate will begin unusual damages to downstream equipment. Hence, the steam condensate must be flushed from the steam line. The equipment that is utilized to wash the steam condensate is called a steam trap. To maintain the steam trap’s reliability, a special survey should be conducted periodically, known as a steam trap survey. 

Through this steam trap survey, we will know the condition of the steam trap and then conduct the needed maintenance action. Most of the industry implemented time-based surveys. Longer interval periods increase the trap’s faulty rates as well as vice versa. Badak LNG performed the 4-yearly survey program on its steam trap’s system. The last survey was conducted in 2012. From 1048 traps, 32% of them found a leak.

The quantified steam loss from these leaking traps is 63.3k tons/year. Also, a typical result has been shown by 2008 survey results in which 33.30% of the trap population found the leak and gave 28.6 k ton/year steam loss. From these results, it’s considered that the existing survey interval should be adjusted to a more reliable pattern to get a significant decrease in trap’s faulty rates. (steam trap survey)

This study explored the plan of implementing a Risk-Based Survey (RBS) to replace the traditional time-based survey. Through RBS, all the established traps are assessed by their type and service pressure, grouped based on the risk, and then decided the initial survey periods for each trap. The principles of RBS rely on how the failure is to occur and how the consequence will be if the failure occurs. Therefore, the traps that have a greater risk will be surveyed in shorter intervals. On the contrary, the lower risk traps will have a longer interval. 

Naturally, a tiny portion of steam gets condensed during the process of delivery. Therefore, the appearance of condensate is critical and will additionally damage the steam piping and downstream equipment. Thus, the condensate must be washed from the steam line through the steam trap. A steam trap is an automatic valve installed on a steam pipe to remove condensate and other pollutants such as air and non-condensable gases. (steam trap survey)

Nowadays, three major steam traps are mostly selected to handle steam systems, i.e., mechanical, thermostatic, and Thermodynamic. For example, the Badak LNG plant has 1412 steam traps. All of these traps should be inspected and repaired periodically to measure the potential losses of steam. The existing periodic survey has been conducted on a 4-yearly basis. After the survey was conducted, the repair or replacement was done. (steam trap survey)

Therefore, we need more advanced methods to reduce the faulty rates effectively.  

The existing steam trap’s survey program Badak LNG has achieved the 4-yearly survey program for every 1412 steam traps. This is the time-based model that is commonly used in other industries. The last steam trap survey was carried out in 2012, covering trap counting and condition checking. Inverted Bucket and Thermodynamic traps individually share 43.2% and 43.6% of the trap’s population. (steam trap survey)

Also, a typical result has been shown by a 2008 survey where 33.30% of the trap’s population was found to leak and gave 28.6 ton/year steam loss. At a typical faulty rate, the 2008 survey shows that the steam loss is 60% smaller than the 2012 survey since most leakages occurred in small to medium pressure of the steam line. 

The role of trap survey 

Each of the installed traps has a definite lifetime, and it is different from each other. The lifetime variation is caused by varied operation conditions, diverse trap populations, and different trap installation/replacement times. (steam trap survey)

The increase in faulty rates is caused by some new leaks that occurred during an in-between period of the survey. On the other side, routine maintenance relies on the type of trap and its application (Bhatia, 2007). The combination of both interval adjustment and traps grouping raises the concept of a risk-based survey. Proposed RBI program API RP 580 values that risk combines the probability of some event occurring during a period of interest and the event’s consequences. In numerical terms, 

Risk = Probability x Consequence.

The purpose of RBI is to define how suitable the incident will occur and how critical is the origin of that incident when it indeed happened. Assessment of risk gets conducted in three ways like(steam trap survey)

qualitatively, 

semi-quantitatively, or 

quantitatively. 

Semi-quantitative, anyhow, is the favored option considering the assessment has combined a professional or engineering judgment and historical data element of special equipment. The result is then numbered and outlined in the risk matrix. This method provides a precise and straightforward determination of risk. RBI helps determine and prioritize the high-risk equipment, and more stringent mitigations are set up to move the risk to acceptable risk. 

The assessment associated with the steam trap survey is directly conducted on the equipment essential since the installation or part assembly is usually simple and faces the same operation condition, i.e. same steam pressure and temperature. The probability of failure (PoF) is evaluated based on the type of steam trap survey, while the consequence of failure (CoF) is evaluated based on service pressure. The mitigations for established risk ranking are replacing more reliable or right trap, stringent inspection frequency, trap’s installation modification, establishing a comprehensive test method, and adjusting the operational procedures.

Usually, frequency of inspection becomes the most effective way of mitigation since stringent monitoring is the key to the successful detection of early abnormal conditions of the steam trap. Hence, risk ranking mitigation is better to focus on establishing the steam trap’s inspection interval. The steam trap risk matrix RBI has been designed to divide the equipment risk based on its probability, likelihood, and consequence or severity. The benefit of both risk elements will then plot on the matrix to get easy reading. The same method can be applied to steam traps in simple 3×3 matrixes, adopted and transformed from API RP 580.

The ranking will then decide the interval of the steam trap’s examination and maintenance. Probability of trap failure Steam traps is allocated to a probability of failure score starting from L (low), M (medium), and H (high), based on the characteristics of traps. They are summarized in The decisive factors that significantly affect the grade probability score are resistance to wear, ability to handle dirt, and ability to respond to the load change. (steam trap survey)

A consequence of trap failure Like a PoF, steam traps are authorized to a consequence of failure (CoF) score from L (low), M (medium), and H (high), relied on steam line service pressure traps. The CoF is directly correlated to the monetary impact. At the same size as the leaking orifice, the higher the steam pressure, the higher the steam loss, thus the higher the monetary loss. The principles of risk-based mitigation rely on how likely the failure is to occur and how the consequence will be if the failure occurs.

Therefore, the trap that has a higher risk will be surveyed in more frequent intervals. Contrary, the lower risk trap will have a longer interval. The base interval value of each risk ranking is as follows: • High risk: 6 monthly • Medium risk: 12 monthly • Low risk: 18 monthly This interval can be further evaluated – shortened or extended – after some periods of a survey which accurate data is available. 

Faulty rate projection Implementing more frequent surveys, the faulty rate will basically decrease by a significant number. Some companies have reported the fact that applied more frequent maintenance at the first time- at minimum a year- and been evaluated for some years afterward. For example, Kashima Oil Co., Ltd – at Kashima Refinery – shows a decrease in trap’s faulty rate by 16.7% in six months and remaining only 0.1% in the next one-half year by implementing a yearly survey interval.

On the other hand, the US Department of Energy has concluded that the minimum proactive maintenance program would reduce the loss rate to about 8%. In comparison, the intermediate program should yield some reducing losses to perhaps 4%. The minimal program is the survey conducted yearly, while an intermediate program is on a 6-monthly basis. In the Badak LNG case, a combination of 6-monthly and yearly surveys can be assumed as the abovementioned risk-based survey and projected to reduce the faulty rate to 5% in the first six months and keep it under 5% afterward, as figured out in Figure-6 below.  

Conclusion 

Summary and conclusion Based on the 2008 and 2012 surveys, the 4-yearly survey provides a high faulty rate of steam trap’s population in the 4th period, causing a significant monetary loss. One of the efforts to reduce the faulty rates is by conducting a Risk-Based Survey. The survey provides more frequent intervals and promotes cost savings since the survey sorts the traps into some groups and prioritizes the high-risk traps then.