Nace Rp 0178 Pdf

[Eri Pfaff]

Periodicinspection of linings and coatings is the key to a long service life of your equipment. The correct time for a check-up depends upon a myriad of factors including operating conditions, type of substance stored, temperature etc. It can also vary based on the protective material installed. Through the inspection process we can identify potential problem areas before they turn into expensive issues and lead to longer down times. With certified NACE and AWS welding Inspectors on staff, all tank inspections are carried out with the highest precision.

The first step of any inspection is to do a thorough visual review of the area. Any obvious defects will be noted for further testing. Afterwards, a holiday test will detect any pinhole leaks to ensure continuity in your lining system. Depending upon the system in place, we may utilize other non-destructive test methods like durometer testing to ensure a fully cured system is in place or a DFT method (Dry Film Thickness) for thin coating systems.

At first, a visual inspection of your fiberglass lining or substrate will be conducted. Visual inspections are crucial, especially for FRP linings. We can then employ a Barcol tester which measures the hardness of the fiberglass linings, ensuring that excessive heat or operating conditions have not weakened the lining system.

In order to apply rubber or PVC lining in your equipment, all welds must be in conformance with NACE/AMPP SP0178-2007-SG standard. Our AWS Certified welding inspectors conduct these inspections to ensure all welds are free of defects and suitable to be lined. At the first stage, the weld inspection is a visual analysis of the joint. Then we can use a fillet gauge to measure size of the fillet weld, weld leg length, and the convexity of the weld to make sure dimensions are in accordance with the blueprint.

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Made from durable T Grade ABS plastic, the comparator comprises of 14 different examples of actual welds, allowing a thorough evaluation to be completed. Each Weld Comparator is supplied complete with a copy of the NACE SP0178-2007 Standard, providing detailed recommendations on design, fabrication and surface finish requirements. It includes generic and graphic descriptions of various degrees of surface finishing of welds that may be specified in preparation for the lining of tanks and vessels. ELCOMETER 999 H99921527 Weld Comparator (STANDARDS: SP0178-2007)

At a power plant in Asia, a total of 120 m of above-grade auxiliary cooling water (ACW) pipe was constructed to convey seawater from ACW pumps to a plate-type heat exchanger. The ACW pipe was a 16-in (406-mm) diameter carbon steel (CS) pipe lined with 8 to 12 mils (0.2 to 0.3 mm) of coal tar epoxy. The pipe spools were joined by flanges. Figure 1 shows the general arrangement of the ACW pipe.

After six months of operation, leaks appeared at welds on lower portions of the pipes. Subsequently, more leaks were found at welds and flanges. After taking apart the pipe spools, it was found that all leaks developed at pipe welds and between the flanges. Less significant corrosion was also observed on areas away from welds and flanges. Figure 2(a) shows some of the pipe spools that were replaced.

When two flanges are joined together in seawater service, crevice corrosion may initiate at any gap between the flanges. The entire ACW piping system had dozens of flanges that were possible sites for crevice corrosion attack. Without a cathodic protection (CP) system for corrosion protection, crevice corrosion could be severe, as shown in Figure 2(b).

Without CP, corrosion developed at coating defects and then crept underneath the coating. Flowing seawater chipped off damaged coating, causing more bare steel areas to be exposed. Figures 2(c) and (d) show the coating failure and corrosion on the pipe body. Unlike crevice corrosion at flanges and welds, this corrosion was localized and would take more time to penetrate the wall.

The most severe corrosion attack occurred at the welds and was caused by crevice corrosion. Due to incomplete weld penetration at some joints, there were gaps at the welds inside the pipe. Moreover, sandblasting during surface preparation was unable to thoroughly clean those gaps and the coating quality was compromised as a consequence. Because of the poor coating quality at the welds and the absence of a CP system in seawater service, crevice corrosion attack at the welds initiated and accelerated.

Corrosion also occurred at welds with excessive weld penetration, but this was relatively minor compared to corrosion of the welds with incomplete weld penetration. In time, however, more corrosion would be expected at or near the welds with excessive penetration caused by the compromised surface preparation. The coating specification called for grinding the welds to NACE SP0178,1 Designation C, Appendix C. Unfortunately, this requirement had not been fulfilled. The corrosion morphology at welds with incomplete penetration is shown in Figures 3(a) through (c), and excessive penetration is shown in Figure 3(d).

It was concluded that CP in conjunction with coating repair would provide adequate corrosion protection. All ACW pipes were above grade, so it was not practical to electrically isolate the ACW pipe, since pipe supports, grounding systems, and other metallic structures contacting the pipe would have made the isolating flanges ineffective.

Figure 1 shows the locations of the anodes and the reference electrodes along the ACW pipe. All probe-type anodes and reference electrodes came with a factory-sealed lead wire. Figure 4 shows part of the auxiliary cooling system while the ICCP system was under construction. Here, 11-in (32-mm) NTP 3000# 316L stainless steel (UNS S31603) half-couplings have been welded on the pipe. The anodes and reference electrodes were threaded into the pipe through the half-couplings. A total of 31 probe anodes were installed. Anode lead wires were routed to the anode junction box, and reference electrode lead wires were routed to the rectifier. Hot-dip galvanized steel conduits were used to accommodate the lead wires.

Surface preparation is critical to coating performance, especially in seawater exposure. Coating specifications shall be strictly followed; QA/QC procedures shall be clearly addressed in the contract and strictly implemented at all stages in the processes.

Each Weld Gauge is supplied complete with a copy of the NACE SP0178-2007 Standard, providing detailed recommendations on design, fabrication and surface finish requirements. It includes generic and graphic descriptions of various degrees of surface finishing of welds that may be specified inpreparation for the lining of tanks and vessels.

The client is asking to use 98% of sulphuric acid as initial concentration and dilute to a concentration before dosing into the process line. In this case, the process line is the raw water from a river. The purpose is to reduce the pH to the optimum pH for the coagulant optimum performance.

Firstly, in terms of the dosage required. I did my calculations and the required amount of Sulphuric acid. The result to lower down the pH from pH 8 to 6 is about 0.49ppm of 10% Sulphuric Acid. This is contradict with the lab result report that it claimed to dose 98% H2SO4 at 20-30ppm. I understand that it could because certain organic matters in the raw water will react with the acid ions, but would it make a such different? I have no idea on what is wrong with my calculations.

Secondly, to calculate the heat of enthalpy of dilution. From my understanding, It is batter to do a higher ratio dilution due to the higher amount of water creates a larger heat dissipating medium to absorb the heat of dilution due to the addition of acid to the water. I get the temperature rising from diluting 98% to 3% is about 30 degree C from my calculation. However, in reality, obviously, the temperature would go up to 180 degree C (boiling), and dilution shall be done by stages 98-60-30-20-10%, with heat removal system after each stages of dilution.

Note that H2SO4 produces H2 (google - hydrogen grooving) while H2O2 produces O2 (google - peroxide decomposition). This means you are unable to avoid pure H2+O2 accumulation in vapor space (equipment) and gas pockets (piping). This mix is the most explosive in this universe and I do not understand how you are planning to deal with this.

88% @ 130C means glass or tantalum. Note that common grade glass lining (e.g. food grade) is not suitable - dedicated design and manufacturing procedure is required. Expensive option I should say. I am not sure you do understand how expensive and dangerous this is. As per my experience some grades of PTFE and graphite are suitable but this is not a widely accepted practice so I cant recommend these.

2.6.6 High-temperature baked phenolic linings and epoxy novolac linings are commonly used in small carbon steel storage tanks if iron contamination is a concern for sulfuric acids in the 90 to 98% concentration range. Tanks that are being considered for lining should be small enough that the lining can be baked. Tank fabrication, surface finish, and design shall comply with NACE Standard RP0178.18 Proper application and curing must be ensured to achieve the long service life normally experienced in sulfuric acid service up to 98% concentration. At acid concentrations above 98%, high-baked phenolic linings have a short service life (see NACE Publication TPC #219 and NACE Standard RP018820). Alternative lining materials are available in addition to high-temperature baked phenolic and epoxy novalac linings. A coating supplier should be contacted for further information. NACE Standard SP059221 and NACE No. 11/SSPC(5) PA 822 contain information relevant to sulfuric acid tanks on the topics of surface preparation, coating selection, application, curing, inspection, and testing.

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