PLANNING FOR MAINTENANCE AND REPAIR OF CONTINUOUS SHIP UNLOADER USING THE IRRO METHOD

. The problem faced is damage, especially to the screw conveyor from the Continuous Ship Unloader (CSU) as a dry bulk material transfer equipment (phosphate rock) which is taken from the ship's hold which is flowed by a screw conveyor followed by the belt conveyor to the material warehouse to be processed into a type of fertilizer. The purpose of planning is to obtain a schedule and estimated cost of maintenance and repair of CSU for the period 2022 to 2025, and to obtain the ratio of maintenance-repair costs to the profit of the machine. Planning methods uses the IRRO (Inspection, Replace, Repair, and Overhoul) method include data collection of machine maintenance history and component breakdowns, checking CSU specifications, making a list of component life predictions and component prices, predicting costs and duration of component dissasembly, screw conveyor repair, maintenance and repair scheduling, and maintenance and repair cost estimates. The real results of planning in the form of a maintenance and repair schedule for the period of 2022 to 2025; maintenance and repair costs respectively for the years 2022 to 2025 are IDR 136,873,000; IDR 335,986,000; IDR 160,687,000; and IDR 464,733,000; and the ratio between maintenance costs to profit for the years 2022 to 2025 is 0.51, 1.22, 0.57, and 1.63 which means the machine is still fit for use without the need for refurbishment because it is still prospective.


INTRODUCTION
Industrial development in Indonesia, especially the chemical industry has increased from year to year. Progress in the industrial sector has a very important role in national development in all fields in order to improve people's welfare. Especially in industries that have a role to support the provision of national fertilizers to achieve food self-sufficiency program and support the economy, especially the agricultural sector. The expansion of the agricultural sector in the early 1970-1980s was inseparable from the role of the fertilizer industry which enabled farmers to optimize the results of the green revolution to increase their production. Along with the increasing area of agricultural land and plantations in Indonesia, the need for fertilizer is increasing from year to year. One of the fertilizer industries in Gresik, east Java, Indonesia is the port of Terminal for Own Activities for loading and unloading activities, one of the equipment used in the loading and unloading process is the CSU (Continuous Ship Unloader). Raw materials that are transported/unloaded are phosphate rock, ZA steel grade, ZA-caprolactam, MOP-red, MOP-white, MOP-pink, sulfur and SP 36. The way CSU works is that the material in the hold of the ship is sucked in through the feeder inlet then followed by a vertical screw conveyor through the horizontal screw conveyor then the material falls through the hopper and the material dust is sucked in by the dust collector at the end of the hopper, so that the material falls on the belt conveyor to be forwarded to the warehouse. Due to the important role of CSU at Terminal for Own Activities, an effective maintenance and repair plan must be made to avoid damage that causes breakdown. p-ISSN : 1412-114X e-ISSN : 2580-5649 http://ojs.pnb.ac.id/index.php/LOGIC Maintenance is an attempt to eliminate the causes of the breakdown, if possible before the congestion occurs. These efforts can take the form of cleaning, lubrication, periodic inspections, servicing, and tune-ups so that their performance remains within the expected performance range. Repair is the treatment of the effects of a congestion event. So the difference between maintenance and repair lies in the effort before the congestion/damage occurs and treatment of the effects after the congestion incident [1] Screw conveyors are generally right-hand with screw designs that are selected according to the material being moved, trough screw or continuous screw is selected to move dry granules or powder. Screw normally made of steel sheet which is welded to the shaft [2].
In operational, maintenance and repair activities must comply with the principles of occupational health and safety (OHS). Safe and healthy at work is the condition of workers that must be realized in the workplace, of course with all efforts based on science and thought to protect workers in accordance with human rights and applicable laws and standards [3].
Total Productive Maintenance/TPM is a treatment related to all elements of the company with the aim of achieving zero product defects, zero breakdown and zero accident. TPM as a maintenance method that maximizes efficiency, solidifies preventive maintenance systems, maximizes productivity, reduces downtime, and motivates all company production lines to avoid sudden repairs and minimize unscheduled maintenance [4]- [5].
Preventive Maintenance (PM) policy is a proactive technique that has been used since the inception of maintenance systems research [6]. The efficiency of PM when applied to leased objects is considered the determinant of revenue for the next rental period [7].
The total average cost per unit time which includes production costs, warranty, and system maintenance is applied to the useful life of the equipment [8].
The case study model of multi-objective genetic algorithm can increase availability, reduce maintenance costs, increase plant profits, can be applied in a continuous operating system for chemical plants with modifications to its operating characteristics [9].
An increase in the predictive maintenance level can lead to a lower quality control cost [10].
The balance between preventive maintenance and corrective maintenance to minimize costs varies between organization and assets, but there is a rule of thumb for balancing preventive maintenance and corrective maintenance with an 80/20 ratio [11].
Preventive maintenance and predictive maintenance are based on a history of maintenance which gives an indication of the degree of damage periodically with possible shifting of component life due to the possible variation in the operating conditions of an equipment. Corrective maintenance is possible if an equipment condition requires adjustment without changing its basic principles in order to keep it functioning. Maintenance and repair costs can increase sharply if good planning is not done, because early symptoms of deterioration are not immediately stopped or reduced through scheduled treatment planning. With scheduled maintenance, unexpected losses can be minimized.

METHODS
Planning methods uses the IRRO (Inspection, Replace, Repair, and Overhoul) method include collecting data on CSU operational history and component failure, reviewing CSU specifications, formulating damage problems, making a list of components to be handled, predicting component life, predicting spare parts prices, predicting repair costs, predicting duration and maintenance costs for components assembly, maintenance and repair scheduling, estimated total annual costs for the period of 2022 to 2025. The CSU as the object of maintenance and repair planning is shown in Figure 1 which is marked by an oval line, the material in the hold of the ship in the right side is sucked in through the feeder inlet then followed by a vertical screw conveyor through the horizontal screw conveyor (yellow color) then the material falls through the hopper and the material dust is sucked in by the dust collector at the end of the hopper, so that the material falls on the belt conveyor to be forwarded to the warehouse in the left side.
The CSU specification is shown in Table 1 [12]. The sections of the CSU are shown in Figure 2 [12].

RESULTS AND DISCUSSION
CSU maintenance is carried out to obtain stable performance by conducting inspection, replace, repair, and overhaul.
Inspection activities to check the cleanliness, good or bad condition of existing components, check whether the existing lubricant/oil/grease is sufficient, insufficient, contaminated or dirty. CSU inspections are carried out every 3-4 months for components and for lubricants, inspections are carried out once a month. Weekly inspections, before and after full retrieval of one hold is carried out by the CSU operator, but by visual inspection and from inside the cabin by checking from the monitor or from the control room. The good synergy between the operator and the maintenance mechanic makes equipment maintenance better.
One such inspection with an example of greasing the end bearing is shown in Figure 3 [12].  Checking the conveyor screw by hearing or from the sound of the motor that increases the load whether the material coming out is unstable or not suitable, if so, then the horizontal arm conveyor casing is opened to check the clearance between the flight screw and the inside of the vertical arm conveyor casing, in case of overclearance due to friction from the material, then the screw conveyor is immediately replaced with a spare screw conveyor, after that contact the Fabrication Department and report the conveyor screw to be repaired or reconditioned.
Replacement of spare parts according to the predicted component life is shown in Table 1 [12]. The price and lifetime predictions of the CSU components are shown in Table 1 [12]. Indonesian currency unit is Rp which is stated in IDR.
Spare parts are replacement components that are prepared based on the limited life time prediction of components due to the limited nature of the material, the shorter the component's life time, the more spare parts that must be prepared. The price of spare parts can be predicted based on the purchase note of the same spare parts in the previous period by adding the price related to inflation to the previous purchase period, for example an increase in price of about 4% per year, if inflation is expected (decrease in the value of money due to the influence of the amount of money in circulation is more than required [1] Calculation of the price of spare parts using formula (1). N = (Initial Price x 4%) + Initial Price (1) where: N : Price prediction for the next period Initial Price: The price of the current/initial period 4% : Inflation per year (as an example) Predictions of spare parts prices can be obtained from sources including: 1) Purchase notes for spare parts, 2) Information from shops selling or supplying spare parts, 3) Price information from the internet online, 4) Workshop where to order spare parts, and 5) Maintenance planners can make predictions based on the function of components relative to other components [1]. The costs and duration of disassembly and assembly of CSU are shown in Table 2 [12].  Idler Wheel  SHS  3  19  21  22  23  Gearbox-EC  SHS  3  19  21  22  23   11   Oil  Hydraulic Oil  SHS  2  19  21  22  23  Gearbox Oil  SHS  2  19  21  22  23  Grease  SHS  2  19  21  22 23 Note: SHS: Senior High School CSU repairs, especially in the reconditioning of screw conveyors, are carried out every 6000 hours or 107 weeks provided that they operate in one day with 1 shift for 8 working hours [12]. The repair work is carried out by the Fabrication Department who has a special duty or a specialist in screw conveyor repair.
The damage that occurs due to erosion of the flight surface due to friction causes the conveyor screw to wear out. The friction that occurs is the friction between the screw conveyor and the material and the casing, because if the material between the flight/blade of screw conveyor and the casing is left alone, the effect will be even greater. The effect of screw conveyor damage is less optimal/efficient in the transportation process. If the friction that occurs is greater, it can cause motor power to be wasted to overcome the friction and a lot of residual material settles on the casing due to not being moved. If this is continued, it can cause more fatal energy wasted because the efficiency of transportation of materials decreases. Figure 5. Examples of worn screw conveyor blades [12] The prediction of material prices for CSU repair activities is shown in Table 3 [12]. Table 3. Predictions of material prices for CSU repair activities [12] No.
PART The process of repairing screw conveyors includes the following stages: 1) The cutting of a duplex plate of 16 mm thick with a width of 25 mm using plasma cutting is shown in Figure  6 [12]. Figure 6. Cutting duplex plates with Plasma Cutting [12] 2) Installation of cylinder shock at both ends of the screw conveyor shaft which serves as a support for the bearings/rollers is shown in Figure 7 [12]. Figure 7. Installation of cylinder shock at both ends of the screw conveyor shaft as a support for the bearing/roller [12] 3) Reduction of the flight screw conveyor to f 585 mm with a lathe is shown in Figure 8 [12]. 4) Coating flight screw conveyor with coating material from duplex plate with a thickness of 16 mm and a width of 25 mm using welding with an electrode E22209 which follows the Welding Procedure Standard. The welding is carried out along the flight screw conveyor on 2 sides which a process called layding/lining is shown in Figure 9 [12]. Figure 9. Coating flight screw conveyor with coating material from duplex plate [12] 5) After cleaning from the crust, the duplex plate is then overlaid or coated on both sides of the duplex plate using the E8838 electrode to exceed f635 mm. The electrode used is similar to the E2209 electrode, but has a higher hardness value, so that the flight screw conveyor surface becomes harder [12]. 6) The finishing process of a flight screw conveyor with a turning using a 6000 mm lathe, the diameter of the flight screw conveyor turned into 635 mm is shown in Figure 10 [12]. Figure 10. The finishing process of a flight screw conveyor with a turning using a 6000 mm lathe [12] 7) The screw conveyor is carried out by a balancing process with a balancing machine to balance its rotation when used and to minimize vibration. 8) Visual check, dye penetrant test, and dimensional check to ensure the quality of repairs, if the screw conveyor does not meet the requirements, it is repaired and if it meets the requirements, then the screw conveyor shown in Figure 11 [12] is ready to be installed into the CSU. Figure 11. Screw conveyor after repaired [12] Overhaul at CSU is carried out every 15,000 hours or 268 weeks provided that it has been operating for one day with 1 shift for 8 hours [12]. Some large and expensive components such as gearbox, motor, and slewing bearings replacement can take up to 2 weeks to take apart with additional overtime. Since CSU maintenance and repair planning has a period limit of 4 years or 11,648 hours or 208 weeks while the overhaul schedule is 15,000 hours or 270 weeks, the overhaul activity does not go into details and cost estimates.
The CSU has a loading/unloading capacity of up to 1000 tons per hour which makes CSU the backbone of loading/unloading activities, however, with the high utility of CSU, the number of damage also increases, even CSU often experiences a breakdown [13]. CSU 1 experienced a breakdown of 52 times from November 2015 to January 2016, so it is necessary to analyze the damage data for the formulation of its maintenance policy by using two alternative policy models, namely repair maintenance policy and preventive maintenance policy. From the calculation results, it is found that the maintenance policy is better for preventive maintenance which has an average machine runtime/period and a smaller repair cost compared to the maintenance repair policy, which is carried out every 7 weeks at a cost of IDR 4,291,241.00 [14].
Using the CSU greatly affects the productivity of loading and unloading activities, because the tonnage yield achieved when unloading using the CSU tool is greater than using other tools, and the unloading is completed faster [15].
An important element in the electric steam power plant (PLTU) is the Ship Unloader (SU) as the main loading and unloading facility for coal fuel from the barge to the stockpile. SU is only treated after damage occurs which is analyzed for treatment planning using the Markov Chain method. The Markov Chain results show that the cost of preventive maintenance at moderate status is decreasing by 84.40% from IDR 1,505,211.50 to IDR 234,820.77 for SU 1 and the cost of preventive maintenance in mildly damaged status decreased by 86.22% from IDR 1,019,642. 35 to IDR 137,893.05 for SU 2 [16].
An example of the results of making a CSU Maintenance and Repair Schedule in the 2023 period is shown in Table 4 [12].

CONCLUSION
The results of planning in the form of a maintenance and repair schedule for the period of 2022 to 2025; maintenance and repair costs for the years 2022 to 2025 are IDR 136,873,000; IDR 335,986,000; IDR 160,687,000; and IDR 464,733,000; and the ratio between maintenance costs to profit for the years 2022 to 2025 is 0.51; 1.22; 0.57; and 1.63 respectively which means the machine is still fit for use without the need for refurbishment because it is still prospective.