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Title: Assessment of the effects of surface preparation and coatings on the susceptibility of line pipe to stress-corrosion cracking

Abstract

Objectives were to evaluate susceptibility of pipeline steel to SCC when coated with coal-tar enamel, fusion-bonded epoxy (FBE), and polyethylene tape coatings. The tests included standard cathodic disbondment tests, potential gradients beneath disbonded coatings, electrochemical measurements, and SCC tests. It was concluded that factors affecting relative SCC susceptibility of pipelines with different coatings are the disbonding resistance of the coating and the ability of the coating to pass cathodic protection (CP) current. FBE coated pipelines would be expected to exhibit good SCC resistance, since the FBE coating had high cathodic disbonding resistance and could pass CP current. Grit blasting at levels used at coating mills may be beneficial or detrimental to SCC susceptibility. Excellent correlation was found between th Almen strip deflection and change in SCC threshold stress. It appears to be beneficial to remove as much mill scale as possible, and a white surface finish probably should also be specified. 50 figs, 10 tabs.

Authors:
 [1]
  1. (Cortest Columbus Technologies, Inc., OH (United States))
Publication Date:
Research Org.:
American Gas Association, Inc., Arlington, VA (United States). Pipeline Research Committee; Cortest Columbus Technologies, Inc., OH (United States)
Sponsoring Org.:
AGA; American Gas Association, Inc., Arlington, VA (United States)
OSTI Identifier:
6799002
Report Number(s):
AGA-93007094
CNN: Project 186-917; TRN: 93-005037
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 03 NATURAL GAS; PIPELINES; CATHODIC PROTECTION; PROTECTIVE COATINGS; CRACKS; DESCALING; ENAMELS; EPOXIDES; NATURAL GAS DISTRIBUTION SYSTEMS; POLYETHYLENES; PROGRESS REPORT; STEELS; SURFACE TREATMENTS; ALLOYS; COATINGS; CORROSION PROTECTION; DOCUMENT TYPES; IRON ALLOYS; IRON BASE ALLOYS; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; ORGANIC POLYMERS; POLYMERS; POLYOLEFINS; SURFACE FINISHING 360105* -- Metals & Alloys-- Corrosion & Erosion; 032000 -- Natural Gas-- Transport, Handling, & Storage

Citation Formats

Beavers, J.A. Assessment of the effects of surface preparation and coatings on the susceptibility of line pipe to stress-corrosion cracking. United States: N. p., 1992. Web.
Beavers, J.A. Assessment of the effects of surface preparation and coatings on the susceptibility of line pipe to stress-corrosion cracking. United States.
Beavers, J.A. 1992. "Assessment of the effects of surface preparation and coatings on the susceptibility of line pipe to stress-corrosion cracking". United States. doi:.
@article{osti_6799002,
title = {Assessment of the effects of surface preparation and coatings on the susceptibility of line pipe to stress-corrosion cracking},
author = {Beavers, J.A.},
abstractNote = {Objectives were to evaluate susceptibility of pipeline steel to SCC when coated with coal-tar enamel, fusion-bonded epoxy (FBE), and polyethylene tape coatings. The tests included standard cathodic disbondment tests, potential gradients beneath disbonded coatings, electrochemical measurements, and SCC tests. It was concluded that factors affecting relative SCC susceptibility of pipelines with different coatings are the disbonding resistance of the coating and the ability of the coating to pass cathodic protection (CP) current. FBE coated pipelines would be expected to exhibit good SCC resistance, since the FBE coating had high cathodic disbonding resistance and could pass CP current. Grit blasting at levels used at coating mills may be beneficial or detrimental to SCC susceptibility. Excellent correlation was found between th Almen strip deflection and change in SCC threshold stress. It appears to be beneficial to remove as much mill scale as possible, and a white surface finish probably should also be specified. 50 figs, 10 tabs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1992,
month = 2
}

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  • Intergranular stress corrosion cracking (IGSCC) of Type 304 stainless steel rate tests (CERT) of specimens machined was evaluated by constant extension from Savannah River Plant (SRP) decontaminated process water piping. Results from 12 preliminary CERT tests verified that IGSCC occurred over a wide range of simulated SRP envirorments. 73 specimens were tested in two statistical experimental designs of the central composite class. In one design, testing was done in environments containing hydrogen peroxide; in the other design, hydrogen peroxide was omitted but oxygen was added to the environment. Prediction equations relating IGSCC to temperature and environmental variables were formulated. Temperaturemore » was the most important independent variable. IGSCC was severe at 100 to 120C and a threshold temperature between 40C and 55C was identified below which IGSCC did not occur. In environments containing hydrogen peroxide, as in SRP operation, a reduction in chloride concentration from 30 to 2 ppB also significantly reduced IGSCC. Reduction in sulfate concentration from 50 to 7 ppB was effective in reducing IGSCC provided the chloride concentration was 30 ppB or less and temperature was 95C or higher. Presence of hydrogen peroxide in the environment increased IGSCC except when chloride concentration was 11 ppB or less. Actual concentrations of hydrogen peroxide, oxygen and carbon dioxide did not affect IGSCC. Large positive ECP values (+450 to +750 mV Standard Hydrogen Electrode (SHE)) in simulated SRP environments containing hydrogen peroxide and were good agreement with ECP measurements made in SRP reactors, indicating that the simulated environments are representative of SRP reactor environments. Overall CERT results suggest that the most effective method to reduce IGSCC is to reduce chloride and sulfate concentrations.« less
  • Intergranular stress corrosion cracking (IGSCC) of Type 304 stainless steel rate tests (CERT) of specimens machined was evaluated by constant extension from Savannah River Plant (SRP) decontaminated process water piping. Results from 12 preliminary CERT tests verified that IGSCC occurred over a wide range of simulated SRP envirorments. 73 specimens were tested in two statistical experimental designs of the central composite class. In one design, testing was done in environments containing hydrogen peroxide; in the other design, hydrogen peroxide was omitted but oxygen was added to the environment. Prediction equations relating IGSCC to temperature and environmental variables were formulated. Temperaturemore » was the most important independent variable. IGSCC was severe at 100 to 120C and a threshold temperature between 40C and 55C was identified below which IGSCC did not occur. In environments containing hydrogen peroxide, as in SRP operation, a reduction in chloride concentration from 30 to 2 ppB also significantly reduced IGSCC. Reduction in sulfate concentration from 50 to 7 ppB was effective in reducing IGSCC provided the chloride concentration was 30 ppB or less and temperature was 95C or higher. Presence of hydrogen peroxide in the environment increased IGSCC except when chloride concentration was 11 ppB or less. Actual concentrations of hydrogen peroxide, oxygen and carbon dioxide did not affect IGSCC. Large positive ECP values (+450 to +750 mV Standard Hydrogen Electrode (SHE)) in simulated SRP environments containing hydrogen peroxide and were good agreement with ECP measurements made in SRP reactors, indicating that the simulated environments are representative of SRP reactor environments. Overall CERT results suggest that the most effective method to reduce IGSCC is to reduce chloride and sulfate concentrations.« less
  • The report describes the results of an evaluation of the stress-corrosion cracking (SCC) resistance of three high-strength, line pipe steels. These steels included an X70 grade containing Mn, V, and Cb, with a ferritic-bainitic microstructure; an X70 grade containing boron (B), with a bainitic structure; and a ferritic X80 grade microalloyed with Mo, Cb, V, and Ti. All three of these steels have been shown, in previous A.G.A. research programs, to have excellent strength, toughness, and resistance to hydrogen sulfide attack. The specimens were evaluated using the standard taper-tension specimen test, in which a specimen of varying cross-section is cyclicallymore » stressed in a hot carbonate-bicarbonate solution at a cracking potential. After cycling, the specimen is examined for cracking and the threshold stress level for stress-corrosion is determined. The B-free X70 steel had a stress-corrosion threshold stress of at least 42 ksi (60 percent SMYS). The B-containing X70 steel had a threshold stress of 50 ksi (70 percent SMYS). The X80 grade had the highest threshold both, in terms of absolute stress (60 ksi) and fraction of SMYS (75 percent). In addition, the crack growth rates for the X70 steels appeared to be lower than those of more conventional grades, although those rates could not be accurately quantified in this program. The X70, B-containing grade and the X80 steel both appear to have significantly better SCC resistance than conventional steels. In particular, the X80 grade may provide a threshold stress for SCC that exceeds the normal operating hoop stress of the pipe. 5 refs., 8 figs., 6 tabs.« less
  • A model for SCC crack initiation and early growth has been developed and used to rationalize the SCC behavior observed in tapered-tension tests (TTT) of line-pipe steels that have been tested under high maximum stress levels with a small amplitude controlled cyclic component in a carbonate-bicarbonate environment. Results presented indicate a good correlation between the observed susceptibility and that predicted with the model. Attention has focussed on modeling SCC thresholds and growth behavior so that data developed under laboratory conditions can be adapted to assess field cracking situations. The model developed and validated deals with SCC threshold behavior and growthmore » of cracks up to about 0.020 inch deep. In its final form the model will be useful in making choices regarding SCC resistant steels and decisions on the growth rate of SCC cracks prior to the formation of a crack whose growth is controlled by fracture mechanics. 26 refs., 11 figs.« less