A Guide for Determining Postweld Heat Treatment Requirements for ASME Code Section VIII Pressure Vessels

1984 ◽  
Vol 106 (1) ◽  
pp. 115-123
Author(s):  
D. D. Carpenter
Keyword(s):  
Heat Treatment ◽  
Decision Trees ◽  
Postweld Heat Treatment ◽  
Pressure Vessels ◽  
Quick Method ◽  
Asme Code ◽  
Section Viii ◽  
Postweld Heat

This paper discusses some uncertainties that occasionally arise when considering postweld heat treatment and presents, by the use of decision trees, a quick method for determining whether or not postweld heat treatment is required.

A Thermal Stress Mitigation Technique for Local Postweld Heat Treatment of Welds in Pressure Vessels

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Chunge Nie ◽  
Pingsha Dong
Keyword(s):  
Heat Treatment ◽  
Thermal Stresses ◽  
Postweld Heat Treatment ◽  
Pressure Vessels ◽  
Cylindrical Vessel ◽  
Spherical Vessel ◽  
Novel Method ◽  
Bull's Eye ◽  
Recommended Guidelines ◽  
Postweld Heat

This paper introduces a novel method for effectively mitigating high thermal stresses caused during local postweld heat treatment (PWHT) of welds in pressure vessels on which traditional heating method such as bull's eye heating arrangement has been proven difficult in meeting Code requirements for avoiding “harmful” temperature gradients. The method involves the use of a secondary heat band (SHB) that strategically positioned at some distance away from primary PWHT heat band (HB) in terms of vessel characteristic length parameter Rt, where R is vessel radius and t wall thickness. The basic principles associated with the SHB based technique are first demonstrated on a simple straight pipe girth weld configuration. Then, applications for treating nozzle welds in more complex spherical vessel, cylindrical vessel, and at end of cylindrical vessel are presented. Finally, a set of recommended guidelines are provided for defining both the SHB size and location for performing local PWHT on welds in three major nozzle/vessel weld configurations.

Considerations for Requiring Intermediate Stress Relief (ISR) for All Weld Types on 2 1/4 Cr-1 Mo-V Reactors

2010 ◽  
Author(s):  
Cathleen Shargay ◽  
Karly Moore ◽  
Timothy D. Breig ◽  
Les P. Antalffy ◽  
Michael M. Basic
Keyword(s):  
Heat Treatment ◽  
Postweld Heat Treatment ◽  
Stress Relief ◽  
Welding Defects ◽  
Before And After ◽  
Asme Code ◽  
Brittle Fractures ◽  
The Cost ◽  
Postweld Heat ◽  
Very High

As an industry consensus, API 934-A is an excellent recommended practice on the materials and fabrication requirements for Cr-Mo reactors. However, it is cautious and somewhat vague on the topic of Intermediate Stress Relief (ISR) versus Dehydrogenation Heat Treatment (DHT) for the different types of welds — which reflects the industry’s varying practices. For the advanced steels, API 934-A states that DHT should only be used with Purchaser approval, and that it should not be used on restrained welds such as nozzle welds. As a result, it is common for a DHT to be permitted on longitudinal and circumferential seams to achieve the cost and schedule savings, and ISR is used for nozzle welds. There are risks to the fabricator however, as the welds remain extremely brittle after DHT (the toughness is restored after postweld heat treatment {PWHT}, and at intermediate levels after ISR), and welding defects that are acceptable per ASME Code criterias can lead to brittle fractures during subsequent fabrication steps. The costs of the repairs and delays can then be very high, especially if the cracking is not detected until after PWHT. This paper shows the risks of acceptable defects causing brittle fractures by fracture mechanics calculations, and presents some case histories of cracking. The relative costs of ISR versus DHT, versus repairs before and after PWHT are also reviewed.

Effect of postweld heat treatment on interface microstructure and metallurgical properties of explosively welded bronze—carbon steel

2018 ◽  
Vol 25 (8) ◽  
pp. 1849-1861 ◽  
Author(s):  
Mohammad Reza Khanzadeh Gharahshiran ◽  
Ali Khoshakhlagh ◽  
Gholamreza Khalaj ◽  
Hamid Bakhtiari ◽  
Ali Reza Banihashemi
Keyword(s):  
Heat Treatment ◽  
Carbon Steel ◽  
Postweld Heat Treatment ◽  
Interface Microstructure ◽  
Metallurgical Properties ◽  
Postweld Heat

Design Formulas of Blind End Closures for High Pressure Vessels

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
R. D. Dixon ◽  
E. H. Perez
Keyword(s):  
High Pressure ◽  
Fatigue Life ◽  
Maximum Stress ◽  
Accurate Determination ◽  
Pressure Vessels ◽  
Stress Distributions ◽  
Fatigue And Fracture ◽  
Asme Code ◽  
Section Viii

The available design formulas for flat heads and blind end closures in the ASME Code, Section VIII, Divisions 1 and 2 are based on bending theory and do not apply to the design of thick flat heads used in the design of high pressure vessels. This paper presents new design formulas for thickness requirements and determination of peak stresses and stress distributions for fatigue and fracture mechanics analyses in thick blind ends. The use of these proposed design formulas provide a more accurate determination of the required thickness and fatigue life of blind ends. The proposed design formulas are given in terms of the yield strength of the material and address the fatigue strength at the location of the maximum stress concentration factor. Introduction of these new formulas in a nonmandatory appendix of Section VIII, Division 3 is recommended after committee approval.

scholarly journals Examining Stress Relaxation in a Dissimilar Metal Weld Subjected to Postweld Heat Treatment

2018 ◽  
Vol 7 (4) ◽  
pp. 20180018
Author(s):  
K. Abburi Venkata ◽  
S. Khayatzadeh ◽  
A. Achouri ◽  
J. Araujo de Oliveira ◽  
A. N. Forsey ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Stress Relaxation ◽  
Postweld Heat Treatment ◽  
Dissimilar Metal ◽  
Dissimilar Metal Weld ◽  
Postweld Heat ◽  
Metal Weld

A Method for Applying Automatic Temperature Control to the Transient Finite Element Analysis of a Pressure Vessel Undergoing Postweld Heat Treatment

2004 ◽  
Author(s):  
Michael Sciascia
Keyword(s):  
Heat Treatment ◽  
Finite Element ◽  
Boundary Conditions ◽  
Temperature Profile ◽  
Pressure Vessel ◽  
Postweld Heat Treatment ◽  
Transient Temperature ◽  
Element Analysis ◽  
Heater Power ◽  
Postweld Heat

For complex finite element problems it is often desirable to prescribe boundary conditions that are difficult to quantify. The analysis of a pressure vessel undergoing postweld heat treatment (PWHT) is an example of such a problem. The PWHT process is governed by Code rules, but the temperature and gradient requirements they impose are not sufficient to precisely describe the complete vessel temperature profile. The imposition of such a profile in the analysis results in uncertainty and errors. A suitable but difficult approach is to specify heater power instead of temperatures, letting the solver determine the temperature profile. Unfortunately, the individual heater power levels necessary to meet the Code requirements are usually not known in advance. Determining the power levels necessary is particularly difficult if a transient solution is required. A means of actively controlling the heaters during the FEA solution is requirement for this approach. A simple and adaptive control algorithm was incorporated into the FEA solver via its scripting capability. Heat flux boundary conditions (heater power) were applied instead of transient temperature boundary conditions. Heater power levels were optimized to achieve predetermined time/temperature goals as the solution proceeded. The algorithm described was successfully applied to a pressure vessel PWHT with 14 zones of control. The approach may be adapted to other problems and boundary conditions.

Effect of Postweld Heat Treatment Conditions on Microstructure of 9Cr-1Mo-V Steel Welds for Pressure Vessel

2017 ◽  
Author(s):  
Hidenori Terasaki ◽  
Tomohiro Tanaka ◽  
Masamitsu Abe ◽  
Mitsuyoshi Nakatani
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Weld Metal ◽  
Postweld Heat Treatment ◽  
Pressure Vessels ◽  
Dislocation Network ◽  
Precipitation Behavior ◽  
Treatment Conditions ◽  
Scanning Transmission ◽  
The Difference

We investigated the effects of post-weld heat treatment conditions on the microstructure of the multi-pass submerged arc weld metal of 9Cr-1Mo-V steel used in pressure vessels. The microstructural properties were analyzed under three conditions (as-weld, Larson-Miller parameter (LMP) = 21.38 × 103, and LMP = 21.99 × 103). The precipitation behavior was observed using scanning electron microscopy, and the difference in precipitation behavior in the “as-welded” and “reheated” regions of the prepared multi-pass weld metal was clarified at the different LMP values. The precipitate was analyzed using scanning transmission electron microscopy. An oxide and two types of precipitates were identified, and a dislocation network pinned by MX-type carbides was visualized under the low-LMP condition. The effects of LMP on the effective grain size and dislocation amount were also evaluated using electron back-scattering diffraction. All microstructural change along the LMP had a positive effect on the toughness of weld metal.

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