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Title: Investigation of a Modified 9Cr-1Mo (P91) Pipe Failure

Abstract

A modified 9Cr-1Mo feedwater (condensate) line at an Eastman Chemical Company plant failed in January 2005. The line was in continuous service since start-up December 2001 until failure. The Plant Superintendent estimated there were three thermal cycles since start-up, although there may have been as many as 25 thermal cycles during commissioning. Normal operating temperature was 325 F (163 C) and pressure was 1762 psig. The line was steam traced with the tracing activated only when ambient outdoor temperature dropped to 40 F (5 C). A modified 9Cr-1Mo steel (P91) pipe failure in a feedwater line in a chemical plant was investigated. The failure occurred in the vicinity of an elbow produced with socket welds of the pipe to the elbow. Based on metallography and hardness measurements, it was concluded that failure occurred because of an improper post-weld heat treatment of the socket weldment.

Authors:
 [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Shared Research Equipment Collaborative Research Center
Sponsoring Org.:
FE USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
974591
Report Number(s):
ORNL/TM-2006/001
AA1510100; FEAA028; TRN: US201008%%488
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHEMICAL PLANTS; COMMISSIONING; FEEDWATER; HARDNESS; HEAT TREATMENTS; METALLOGRAPHY; OUTDOORS; START-UP; STEAM; STEELS

Citation Formats

Klueh, Ronald L, and Shingledecker, John P. Investigation of a Modified 9Cr-1Mo (P91) Pipe Failure. United States: N. p., 2006. Web. doi:10.2172/974591.
Klueh, Ronald L, & Shingledecker, John P. Investigation of a Modified 9Cr-1Mo (P91) Pipe Failure. United States. doi:10.2172/974591.
Klueh, Ronald L, and Shingledecker, John P. Sat . "Investigation of a Modified 9Cr-1Mo (P91) Pipe Failure". United States. doi:10.2172/974591. https://www.osti.gov/servlets/purl/974591.
@article{osti_974591,
title = {Investigation of a Modified 9Cr-1Mo (P91) Pipe Failure},
author = {Klueh, Ronald L and Shingledecker, John P},
abstractNote = {A modified 9Cr-1Mo feedwater (condensate) line at an Eastman Chemical Company plant failed in January 2005. The line was in continuous service since start-up December 2001 until failure. The Plant Superintendent estimated there were three thermal cycles since start-up, although there may have been as many as 25 thermal cycles during commissioning. Normal operating temperature was 325 F (163 C) and pressure was 1762 psig. The line was steam traced with the tracing activated only when ambient outdoor temperature dropped to 40 F (5 C). A modified 9Cr-1Mo steel (P91) pipe failure in a feedwater line in a chemical plant was investigated. The failure occurred in the vicinity of an elbow produced with socket welds of the pipe to the elbow. Based on metallography and hardness measurements, it was concluded that failure occurred because of an improper post-weld heat treatment of the socket weldment.},
doi = {10.2172/974591},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Apr 01 00:00:00 EST 2006},
month = {Sat Apr 01 00:00:00 EST 2006}
}

Technical Report:

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  • The weldability of thick sections of Modified 9Cr-lMo steel (Grade 91) has been investigated. The alloy has excellent fabricability. It is not susceptible to hot cracking on stress relief cracking. It is, as are most highly hardenable steels, susceptible to hydrogen assisted cracking but it can be avoided by good shop practice. A soft zone can occur in the heat-affected-zone which can result in Type IV cracking in service. This can be avoided through design or fabrication sequence. Strength reduction factors may also be applied. Thick sections have been successfully welded with the submerged arc, shielded metal arc and gasmore » tunsten arc processes. The alloy because of its higher allowable stress values (2 1/2 times higher than 2 1/4CR-lMo steel at 1050{degrees}F) (566{degrees}C) permits the design of considerable thinner header sections. Further, the alloy is a viable replacement for austenitic materials at temperatures up to 1100{degrees}F (593{degrees}C) thereby eliminating or minimizing austenitic-to-ferritic dissimilar metal joints.« less
  • This report describes the development and testing of a cast version of the popular ASME P-91 ferritic stainless steel. ASME and ASTM have approved its use in pressure vessels and boilers. The allowable strength level of the cast material is slightly lower than that of P- 91 wrought steel. The report also describes shop and field welding procedures developed for the cast steel. Figs, tabs.
  • The weldability of modified 9Cr-1Mo steel has been investigated by numerous organizations including Oak Ridge National Laboratory over a period of several years. The results of the various studies are summarized. Weldability evaluations have included hot cracking susceptibility, reheat cracking response, hydrogen-assisted cracking susceptibility, and the selection of consumables for three welding processes. Weldment mechanical properties have been determined for the gas tungsten arc, submerged arc, and shielded metal arc welding processes. Dissimilar metal weldments between modified 9Cr-1Mo steel and austenitic stainless steels have been produced with good results. Evaluation of the weldments and various tests has indicated that theremore » are no major concerns regarding the weldability of modified 9Cr-1Mo steel.« less
  • This report documents the planning, testing, and technology transfer activities that have been carried out in developing modified 9Cr-1Mo steel (T-91) for liquid-metal reactor (LMR) applications.
  • Results of room- and elevated-temperature tensile tests are reported from tests conducted on three heats of Modified 9Cr-1Mo steel. The heats were thermally aged at various temperatures from 482 to 704{degree}C and at aging time to 50,000 h. Tensile strain rates were also varied in order to determine strain rate sensitivity of tensile properties. Changes in the yield and tensile strengths occurred following exposure to these temperatures with decreases noted at the higher temperatures. The material showed a strain-rate sensitivity particularly at temperatures in excess of about 538{degree}C due to the presence of what was believed to be strain aging.more » The tensile-strength data were parameterized in order to permit estimates of changes in both the room- and elevated-temperature properties to be made following exposure for prolonged periods in service. Estimates are given of the changes in yield and tensile strengths following isothermal exposure a several temperatures for 60 yeas of service time. Comparisons are also made between estimated degradation in short-term properties of Modified 9Cr-1Mo steel and several other materials due to thermal aging. 5 refs., 11 figs., 5 tabs.« less