Effects of Inline Inspection Sizing Uncertainties on the Accuracy of the Largest Features and Corrosion Rate Statistics

2010 ◽  
Author(s):  
Luc Huyse ◽  
Albert van Roodselaar
Keyword(s):  
Corrosion Rate ◽  
Time Interval ◽  
Corrosion Rates ◽  
Course Of Action ◽  
Distribution Parameters ◽  
Statistical Analysis Method ◽  
The Difference ◽  
External Corrosion ◽  
The Cost ◽  
Subsea Pipelines

With the increased acceptance of the use of probabilistic fitness-for-service methods, considerable effort has been dedicated to the estimation of the corrosion rate distribution parameters. The corrosion rate is typically computed from the difference in anomaly size over a specific time interval. The anomaly sizes are measured through either in-line inspection or direct assessment. Sizing accuracies for inline inspection methods are reasonably well established and in many cases the sizing uncertainty is non-negligible. In many approaches that are proposed in the literature the time-averaged corrosion rates are computed without explicitly considering the effect of the sizing uncertainties and as a result considerable interpretation and engineering judgment is required when estimating corrosion rates. This paper highlights some of the effects of the sizing uncertainties and the resulting biases that occur in the subsequent reliability calculations. These assessments are used to determine the most appropriate course of action: repair, replacement, or time of next inspection. The cost for repair or replacement of subsea pipelines is much higher than for onshore pipelines. For subsea applications, it is therefore paramount that the risk calculations, and therefore the corrosion rate estimates, be as accurate as possible. In subsea applications, the opportunity to repair individual defects is often limited due to practical constraints and there is merit in an approach that focuses on entire spools or pipeline segments. The proposed statistical analysis method is ideally suited to this application although the principles behind the analysis apply equally well to onshore lines subject to either internal or external corrosion threats.

External Corrosion Growth-Rate From Soil Properties

2010 ◽  
Author(s):  
Khalid A. Farrag
Keyword(s):  
Growth Rate ◽  
Corrosion Rate ◽  
Soil Properties ◽  
Growth Rates ◽  
Soil Conditions ◽  
Soil Parameters ◽  
Time Interval ◽  
Soil Redox Potential ◽  
Corrosion Rates ◽  
External Corrosion

External corrosion growth rate is an essential parameter to establish the time interval between successive pipe integrity evaluations. Actual corrosion rates are difficult to measure or predict. NACE Standard RP0502 [1] recommends several methods including comparison with historical data, buried coupons, electrical resistance (ER), and Linear Polarization Resistance (LPR) measurements. This paper presents a testing program and procedure to validate the use of the LPR and ER methods to enhance the estimation of corrosion growth rates and improve the selection of reassessment intervals of gas transmission pipelines. Laboratory and field tests were performed using the LPR and ER technologies. The evaluation of soil parameters that affect localized corrosion included its type, moisture content, pH, resistivity, drainage characteristics, chloride and sulfite levels, and soil Redox potential. The results show that the LPR device provides instantaneous measurement of corrosion potential and it may be used to reflect the variations of corrosion rates with the changes of soil conditions, moisture, and temperature. However, LPR measurements are more efficient in saturated soils with uncertainty about its validity in partially and totally dry soils. Consequently, seasonal changes in soil conditions make it difficult to estimate total corrosion growth rate. On the other hand, the measurements using the ER method provided consistent estimates for long-term corrosion growth rates. Corrosion growth rates were also evaluated from a previous study by the National Institute of Standards (NIST) [2]. A procedure was developed to correlate soil properties to corrosion rates from the ER measurements and NIST data. The procedure was implemented in a computer program to provide an estimate of corrosion rate based on the soil input data and allows the operator to use the ER probes to improve the reliability of corrosion rate estimates.

Predicting Corrosion Rates for Onshore Oil and Gas Pipelines

2006 ◽  
Author(s):  
J. M. Race ◽  
S. J. Dawson ◽  
L. Stanley ◽  
S. Kariyawasam
Keyword(s):  
Corrosion Rate ◽  
Growth Rates ◽  
Oil And Gas ◽  
Cost Effective ◽  
Management Plan ◽  
Assessment Method ◽  
Internal Corrosion ◽  
Corrosion Rates ◽  
External Corrosion ◽  
Comparison Of The Results

One of the requirements of a comprehensive pipeline Integrity Management Plan (IMP) is the establishment of safe and cost effective re-assessment intervals for the chosen assessment method, either Direct Assessment (DA), In-Line Inspection (ILI) or hydrotesting. For pipelines where the major threat is external or internal corrosion, the determination of an appropriate re-inspection interval requires the estimation of realistic corrosion growth rates. The Office of Pipeline Safety (OPS 2005) estimate that the ability to accurately estimate corrosion rates may save pipeline companies more than $100M/year through reduced maintenance and accident avoidance costs. Unlike internal corrosion, which occurs in a closed system, the rate of the external corrosion reaction is influenced by a number of factors including the water content of the soil, the soluble salts present, the pH of the corrosion environment and the degree of oxygenation. Therefore the prediction of external rates is complex and there is currently no method for estimating corrosion rates using either empirical or mechanistic equations. This paper describes a scoring model that has been developed to estimate external corrosion growth rates for pipelines where rates cannot be estimated using more conventional methods i.e., from repeat in-line inspection data. The model considers the effect of the different variables that contribute to external corrosion and ranks them according to their effect on corrosion growth rate to produce a corrosion rate score. The resulting score is then linked to a corrosion rate database to obtain an estimated corrosion rate. The methodology has been validated by linking the calculated corrosion rate scores to known corrosion rate distributions that have been measured by comparison of the results from multiple in-line inspection runs. The paper goes on to illustrate how the estimated corrosion rates can be used for the establishment of reassessment intervals for DA, ILI and hydrotesting, comparing the benefits of this approach with current industry recommended practice and guidance.

Corrosion Problems in Sugar Factories in Mauritius

2011 ◽  
Vol 110-116 ◽  
pp. 1983-1989
Author(s):  
L. Tengur ◽  
B.Y.R. Surnam
Keyword(s):  
Corrosion Rate ◽  
Sugar Cane ◽  
Low Carbon Steel ◽  
Extraction Process ◽  
Low Carbon ◽  
Stainless Steel 316L ◽  
Electrochemical Tests ◽  
Corrosion Rates ◽  
Juice Extraction ◽  
The Cost

In Mauritius, corrosion costs forms a large part of the expenses of sugar cane mills and presently there has not been any study on this issue. The present study was therefore performed at one of the sugar cane mills in Mauritius so as to identify the different modes of corrosion degradation and the corrosivity of commonly used metals with respect to the corrosive fluids (mainly juices) encountered in the juice extraction process. The cost associated with the corrosion degradation was eventually calculated. Electrochemical tests were performed to measure and compare the corrosion rate for the metals in the corrosive fluids. It was observed that the highest and the lowest corrosion rates were recorded for pre-extractor mill juice and syrup respectively. Low carbon steel generally had the fastest corrosion rate while stainless steel 316L corroded the least. Finally, from gathered data, the cost of corrosion was found to be 6.6% of the turnover of the factory.

The Stern-Geary and related methods for determining corrosion rates

1975 ◽  
Vol 28 (2) ◽  
pp. 243 ◽  
Author(s):  
DB Matthews
Keyword(s):  
Corrosion Rate ◽  
Corrosion Potential ◽  
Transfer Coefficients ◽  
Corrosion Rates ◽  
Linear Current ◽  
Reversible Potential ◽  
Special Cases ◽  
The Difference ◽  
Current Potential

Calculation of the current-potential relations for corroding electrodes as a function of the cathodic and anodic transfer coefficients and as a function of the difference between the corrosion and reversible potentials demonstrates the deficiencies of the Stern-Geary equation for determining corrosion rates. The calculations also demonstrate that a linear current-potential relation is not predicted except over very small ranges of potential, e.g. 2 mV. As a consequence, it is essential in using the Stern- Geary and related methods to determine the slope dE/di at the corrosion potential. The Stern-Geary method is not applicable for systems where the corrosion potential is close to the reversible potential for either of the participating reactions and fortuitous linearity of currentvoltage plots may be erroneously interpreted as indicating that the Stern-Geary method is applicable. Methods of determining the corrosion rate which depend upon measuring the difference ΔE in corrosion and reversible potentials are not likely to be successful because of their sensitivity to the value of ΔE. A new derivation of the slope dE/di at the corrosion potential is presented and it is shown that the Stern-Geary and Mansfeld-Oldham equations may be derived as special cases. This new derivation is not immediately useful for determining the corrosion rate but it is shown that by measuring the dependence of the corrosion potential on concentration of cathodic reactant then the new derivation can be useful for rapid and accurate corrosion rate measurements even for small values of ΔE.

scholarly journals Adsorption behavior and corrosion rate model of sodium carboxymethyl cellulose (Na-CMC) polymer on aluminium in HCl solution

2020 ◽  
Vol 39 (2) ◽  
pp. 369-378
Author(s):  
O.M. Egbuhuzor ◽  
I.C. Madufor ◽  
S.C. Nwanonenyi ◽  
J.O. Bokolo
Keyword(s):  
Weight Loss ◽  
Corrosion Rate ◽  
Carboxymethyl Cellulose ◽  
Water Bath ◽  
Sodium Carboxymethyl Cellulose ◽  
Time Interval ◽  
Adsorption Behaviour ◽  
Before And After ◽  
The Difference ◽  
Cr Concentration

Adsorption behaviour and corrosion rate of Sodium carboxymethyl cellulose on aluminium was studied. Different concentration levels of Sodium carboxymethyl cellulose (Na-CMC) solution were applied on several prepared and polished aluminium coupons for a corrosion experiment. These coupons were totally immersed in 100ml of 0.5M solution of Hydrochloric acid (HCl) in an open beaker placed in a water bath at varying temperatures for 2-8hrs respectively. At every specified temperature and time interval, the immersed coupon specimen was withdrawn from the test solution, washed, dried and reweighed. The weight loss being the difference in weight of the specimen before and after immersion in the water bath was recorded for every coupon sample. The effects of concentration, temperature and time on corrosion rate were studied and from the various plots, it was observed that increase in the concentration of the inhibitor decreases the corrosion rate. The study of the adsorption behaviour showed that Na-CMC was physically adsorbed on the aluminium coupons and obeyed Freundlich adsorption isotherm with an activation energy of 32K.83j/mol and heat of adsorption of -18.21Kj/mol . The study also established a relationship between the corrosion rate, CR; concentration, C; temperature, T; and time t, through a mathematical model: CR = 3.8-5*T1.1617 - 0.00052t0.6176 - 0.0013C0.8012, the proportion of variance explained (R2) = 0.8658 (86.58%), From the Results of the experiment and the model, Na-CMC was found to be an active corrosion inhibitor of Aluminium in acidic environment. Keywords: Adsorption, Aluminium, concentration, Corrosion Rate, Weight Loss

Determination of the Corrosion Rate of a MIC Influenced Pipeline Using Four Consecutive Pig Runs

2006 ◽  
Author(s):  
Giorgio G. J. Achterbosch ◽  
Lech A. Grzelak
Keyword(s):  
High Pressure ◽  
Corrosion Rate ◽  
Simple Calculation ◽  
Data Set ◽  
Average Value ◽  
Corrosion Rates ◽  
Time Period ◽  
Inspection Policy ◽  
Average Corrosion Rate ◽  
External Corrosion

In-line inspections have been part of the verification of pipeline integrity since the late seventies in N.V. Nederlandse Gasunie. The discovery of external microbial corrosion (MIC) in 1999 in one of the high pressure pipelines changed the inspection policy from inspection of a randomly selected pipeline once every 5 year to an inspection program for the whole high pressure grid (approximately 5.600 km) to be completed in 10–12 years. One of the MIC influenced lines is used to qualify MFL-pig from different suppliers. In the time period 1999–2004 4 different MFL qualification runs have taken place, resulting in 18 excavations. Rather simple calculation of corrosion rates after every pig run indicated values of 0.2–0.3 mm/yr as an average value for the MIC corrosion. After the fourth pig run (5 years after the first) Gasunie decided to determine the corrosion rate also in a more sophisticated way. In coorperation with the mathematical department of the Technical University of Delft statistical analyses were performed. The paper describes how the data from pig runs and excavations was used to extract a suitable subset of corrosiondefects for which the corrosion rate was determined. It was decided to use only these defects that were indicated by all suppliers as external corrosion thereby leaving out defects that were indicated as “mill defect but possibly corrosion”. A second criterion was that a defect has to be reported by at least three of the four suppliers. These criteria resulted in a subset of 52 defects to be analyzed. All of the reported defect depths were corrected for the bias that was determined from the excavation results. The corrected values were then used to calculate the corrosion rate using three approaches: calculation of the corrosion rate for every defect in two ways and calculation of the corrosion rate for the pool of defects assuming a corrosion growth that is linear in time. The average corrosion rate for the defects was in the range of 0.12 to 0.24 mm/yr. Dividing the data set into deep and shallow defects showed that the average corrosion rates for both subsets, 0.23 mm/yr and 0.25 mm/yr, are not significantly different. This underpins one of the assumptions that the corrosion rate is constant. Further discussion within Gasunie is envisaged to determine how these values can be used in the calculation of re-inspection intervals for this line. And at the same time another discussion will focus on whether these values can be used on other lines.

scholarly journals Dynamic Programming to Solve Picking Schedule at the Tea Plantation

2018 ◽  
Vol 7 (4.30) ◽  
pp. 285
Author(s):  
Siti Mahsanah Budijati ◽  
Bermawi Priyatna Iskandar
Keyword(s):  
Dynamic Programming ◽  
Regression Method ◽  
Second Step ◽  
Time Interval ◽  
Rolling Schedule ◽  
Tea Plantation ◽  
Total Cost ◽  
Schedule Time ◽  
The Difference ◽  
The Cost

The tea picking schedule at PT Perkebunan Ciater is set to be the same for all plantation blocks. In fact, the altitude from sea level and the pruning age of each plantation block is different, this results in the difference of buds’ growth. The implementation of the same picking schedule causes the quality and quantity of tea buds often could not be fulfilled. This research is to determine the precise picking schedule by considering the buds’ growth of each plantation block. Two steps are implemented to solve the problem. The first step is to look for picking period and the pattern of buds’ quality for each plantation block, which corresponds to the altitude of the location and the pruning age. The regression method is applied in this first step. The buds’ quality pattern is then used to determine the cost of decreasing buds’ quality and the costs of the buds that left in the plantation. The second step is to develop the picking schedule using dynamic programming, which minimizes the total cost of picking. In addition to this, we also develop a rolling schedule, which schedule time interval is three days. The model results show that the proposed schedule gives a better total cost than the current schedule and the buds’ quality target is easier to achieve.

Experimental Results to Design Lactic Acid for Carbonate Acidizing

2021 ◽  
Author(s):  
Luai Alhamad ◽  
Basil Alfakher ◽  
Abdullah Alrustum ◽  
Sajjad Aldarweesh
Keyword(s):  
Lactic Acid ◽  
Corrosion Rate ◽  
Formic Acid ◽  
Corrosion Damage ◽  
Injection Rate ◽  
Corrosion Rates ◽  
Molecular Weight Difference ◽  
The Difference ◽  
Carbonate Acidizing ◽  
Hcl Concentration

Abstract Acidizing deep carbonate formations by Hydrochloric acid (HCl) is a complex task due to high reaction and corrosion rates. Mixing organic acids with HCl is a typical method to reduce the acid's reactivity and corrosivity. Lactic acid has not been investigated completely in the area of carbonate acidizing. Lactic acid has a dissociation constant similar to formic acid, which is approximately 10 times larger than acetic acid. Therefore, the objective of this work is to compare lactic/HCl blends with plain HCl and formic/HCl blends. Corrosion tests were conducted at high temperature on C-95 steel coupons to investigate associated corrosion damage. Coreflood tests were performed on Indiana limestone cores to mimic matrix acidizing treatment and to investigate amount of pore volumes required to breakthrough. All blends were prepared to be equivalent to 15 wt% (4.4 M) HCl for comparison. Lactic and formic acid concentrations were set to be (0.5 or 1 M), and HCl concentration was calculated as appropriate to reach a blend with strength of 4.4 M. In terms of corrosivity evaluation, blends of lactic and HCl acids showed a corrosion rate of up to 1.97 lb/ft2 at 300°F. The formic and HCl blend showed a corrosion rate of 1.68 lb/ft2 at the same temperature. The difference in corrosion rates between the two mixtures is due to molecular weight difference between lactic and formic acids. When both acids were prepared at 1 M, lactic acid blend required more HCl to be equivalent to 15 wt% HCl acid which was associated with an increase in corrosion rate. Coreflood results established acid efficiency curves for lactic/HCl acid blends. The curves highlighted the correlation between acid-core reactivity, injection rate, and dissolution pattern. Lactic/HCl blend was less reactive than formic/HCl mixture as the last required lower injection rate to obtain optimum pore volume to breakthrough at 300°F. Lactic/HCl blend was able to generate an optimum dissolution pattern as a dominant wormhole was shown on tested core plugs inlet face. This study expands the investigation of lactic acid utilization in carbonate acidizing. Major advantages rendered by using lactic acid with HCl include: (1) favorable dissolution pattern due to lactic acid being less reactive than HCl or formic acids, and (2) less corrosion rates comparing to HCl, that can reduce allocated costs for maintenance and replacements.

scholarly journals How to Use CA-125 More Effectively in the Diagnosis of Deep Endometriosis

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Marco Aurelio Pinho Oliveira ◽  
Thiers Soares Raymundo ◽  
Leila Cristina Soares ◽  
Thiago Rodrigues Dantas Pereira ◽  
Alessandra Viviane Evangelista Demôro
Keyword(s):  
Area Under The Curve ◽  
Severe Form ◽  
Ca 125 ◽  
Time Interval ◽  
Menstrual Phase ◽  
Deep Endometriosis ◽  
The Difference ◽  
Two Phases ◽  
The Cost ◽  
And Control

Deep infiltrative endometriosis (DIE) is a severe form of the disease. The median time interval from the onset of symptoms to diagnosis of endometriosis is around 8 years. In this prospective study patients were divided into two groups: cases (34 DIE patients) and control (20 tubal ligation patients). The main objective of this study was to evaluate the performance of CA-125 measurement in the menstrual and midcycle phases of the cycle, as well as the difference in its levels between the two phases, for the early diagnosis of DIE. Area Under the Curve (AUC) of CA-125 in menstrual phase and of the difference between menstrual and midcycle phases had the best performance (both with AUC = 0.96), followed by CA-125 in the midcycle (AUC = 0.89). The ratio between menstrual and midcycle phases had the worst performance. CA-125 may be useful for the diagnosis of deep endometriosis, especially when both are collected during menstruation and in midcycle. These may help to decrease the long interval until the definitive diagnosis of DIE. Multicentric studies with larger samples should be performed to better evaluate the cost-effectiveness of measuring CA-125 in two different phases of the menstrual cycle.

Erfolg der Jungwaldpflege im Schweizer Mittelland? Analyse und Folgerungen (Essay)

2013 ◽  
Vol 164 (9) ◽  
pp. 262-270 ◽  
Author(s):  
Peter Ammann
Keyword(s):  
Stand Development ◽  
Negative Effects ◽  
Tree Species Composition ◽  
Natural Processes ◽  
Course Of Action ◽  
Tree Thinning ◽  
Swiss Plateau ◽  
Self Differentiation ◽  
The Cost ◽  
Young Growth

Is young growth tending successful in the Swiss Plateau region? Analysis and implications (essay) The effect of the cost-intensive young growth tending used up to the present in the region of the Swiss Plateau is analysed using different approaches. It is evident that young growth tending is not only ineffective with respect to diameter growth but even hinders stand development. Negative effects on quality from young growth tending are also recognised. This is often due to premature interventions in the natural processes of self-differentiation and subsequent systematic errors in the thinning. Furthermore, the effect of tending measures on the tree species composition is often overestimated because in the first 10 to 20 years of stand development, it is primarily the rejuvenation strategy and the site which are decisive. As an alternative course of action, tending concepts are proposed which rely on biological rationalisation and future tree thinning, to achieve future trees which are as vigorous as possible. These are not only more effective, but are also significantly less expensive.

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