Internal Inspection Of Wet Gas Lines Subject To Top Of Line Corrosion™
The Bongkot field is a high CO2 (>20%) wet gas field located in the Gulf of Thailand. Thirteen infield carbon steel sea lines are laid in 80 meters of water. The lines sizes are 14 to 22. Almost 2/3 of the lines circumferences remain in contact with sea water; 1/3 buried on the sea bed by natural burial. The average flowing temperature at wellhead is about 90oC but declines rapidly to almost ambient temperature after a few kilometres. The major part of heat transfer through the pipe wall takes place along the first 500 meters after touch down. Due partial line burial, heat exchange takes place on the upper half section in contact with relatively cool sea water current (18 deg C) causing severe water condensation on the internal pipe surface. The flow regime is stratified at the inlet of the dogleg. Top of Line Corrosion (TLC) is expected along the first few kilometres. Some of lines were inspected by Magnetic Flux Leakage (MFL) inspection tools and severe TLC Local Law 152 Explained By AKAM™
Local Law 152 was passed in 2016 by the NYC Department of Buildings (DOB), requiring gas piping systems of all buildings to be inspected at least every five years by a licensed master plumber. Properties classified as R-3 occupancy or newer buildings, where an inspection has recently taken place are exempt. The law was enacted to protect New Yorkers after several deadly gas explosions occurred in the city.
All exposed gas lines from point of entry into a building, including service meters, up to individual resident spaces are inspected for evidence of excessive atmospheric corrosion or piping deterioration that has resulted in a dangerous condition, illegal connections, and non-code compliant installations. The inspecting party shall also test public spaces, hallways, corridors, and mechanical and boiler rooms with a portable combustible gas detector to determine if there is a gas leak. “This testing is only done for public spaces on floors that contain gas piping or gas utilization equipment.” says Andy Leight, AKAM Senior ll152 due dates Vice President.
When should a Local Law 152 inspection be scheduled?
“If you’re in Community Districts 1, 3, or 10 you should schedule your inspection as soon as possible as your due date is December 31st of this year. For properties in other districts AKAM recommends scheduling your inspections in the Spring or Summer months, well in advance of heating season.” according to Adam Stern, AKAM Senior Vice President. Due to the age and condition of most building’s piping systems, there could be issues that arise requiring a building’s gas service to be shut down for necessary repairs.
The due date cycles for the Community Districts are:
- Community Districts 1, 3, & 10: Jan 1, 2020-Dec 31, 2020
- Community Districts 2, 5, 7, 13, & 18: Jan 1, 2021-Dec 31, 2021
- Community Districts 4, 6, 8, 9, & 16: Jan 1, 2022-Dec 31, 2022
- Community Districts 11, 12, 14, 15, & 17: Jan 1, 2023-Dec 31, 2023
After inspection, what is the responsibility of the property owner?
Within 30 days of inspection, the licensed master plumber must provide the property with a Gas Piping System Periodic Inspection Report showing the results of the inspection. The owner then must submit to the New York State Department of Public Service a Gas Piping System Periodic Inspection Certification signed and sealed by the licensed master plumber who conducted the inspection. “Failure to file by your scheduled due date may result in a $10,000 fine.” says Gina Fazzalaro, AKAM Vice President.
What happens if a problem is found during the inspection?
If an unsafe condition is found, the licensed master plumber must report the issue to the utility providing gas service to the building, and the New York State Department of Public Service. The building owner then must take immediate action to obtain the required permits. Correct issues in compliance with the New York City Construction Codes. “The property has 120 days to resolve the situation and file a new Inspection Certification signed and sealed by the licensed master plumber who conducted the inspection, stating that the conditions have been corrected.” notes Mark Weil, AKAM Vice President.
How can I be sure not to miss my Local Law 152 inspection date?
AKAM tracks Local Law 152 due dates, creates the RFP for services specific to the property’s needs, solicits and levels bids from vetted service providers, schedules the inspection, and submits the certification to the New York State Department of Public Service to ensure all client properties are in compliance. “Our management team attends the inspection of all AKAM managed properties in order to take immediate action should an issue arise.” says Michael Rogoff, AKAM President.
">dob gas authorization was detected. Being confronted with the decision to de-rate the pipeline or even worse to repair some corroded sections, the authors have tried to obtain accurate remaining wall thickness measurement by other mean than Magnetic Flux Leakage pig. IRISPig was developed and the new inspection of one of the lines shown only 50% of the thickness loss measured by MFL.
CORROSION MITIGATION AND FIRST INSPECTION RESULTS
For the development of the Bongkot field, carbon steel was used with 5 mm of corrosion allowance. Selections of pipeline material and corrosion control system was based on the corrosivity evaluation considering CO2 content of the effluent, operating conditions and produced water chemistry. However, no information was available concerning the acetic acid content of the effluent, which is very important for top of line corrosion, during the first phase of filed development. The field conditions being considered as very corrosive, corrosion inhibitor selection for the bottom line corrosion control was a critical issue. A water soluble corrosion inhibitor was selected after intensive laboratory testing(1). Field testing of the selected product confirmed laboratory results as the corrosion rates in the topside piping was reduced to less than 0.1 mm/y. The same product has been continuously injected at the well head for the protection of top side facilities and sealines since the production start up in mid 1993.
The first magnetic flux leakage (MFL) pig surveys carried out in 1994 (one year after first gas) gave no corrosion warning, and the subsequent surveys were set at 3 year intervals. During the 1998 campaign a pattern of TLC mainly from the 10 o?clock to the 2 o?clock position was detected along the first 500 meters (from the Wellhead Platforms) of the pipelines. Moreover, during subsequent inspections (2000 and 2002), the TLC was noticed to continuously propagate in width, length and but not in depth (surprisingly, the deepest features were reported declining). However longer sections of lines were found affected during subsequent inspections.
Following the first indications of TLC, a laboratory study was initiated for corrosion inhibitor selection for batch treatments. Laboratory tests showed that water soluble corrosion inhibitors have better performances to control TLC than oils soluble ones(2). The corrosion inhibitor which has been used for the continuous injection was found to be very effective also for top of line corrosion control. Regular batch treatments have been implemented in all sealines using double pigs (diluted inhibitor is placed between two pigs).