3.08.operatingprocedures.macro etch and hardness testing of welds
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3.08 WELDING PROCEDURES MANUAL Page 1 of 2
OPERATING PROCEDURES
MACRO ETCH AND HARDNESS TESTING OF WELDS
12/31/06
HIS SECTION PROVIDES STANDARD PROCEDURES FOR MACRO ETCH AND
HARDNESS TESTING of welds performed in conjunction with testing of in-service
welding procedures. T
GENERAL
MACRO ETCH TESTING
Macro etch testing (normally used with other destructive testing methods during
qualification of in-service pipeline welding procedures) evaluates the macro-structure of
a weld’s heat-affected zone for anomalies. An etchant is used to clarify the weld
structure; and magnification is used to clarify the view. For permanent test records,
photomacrographs are commonly developed.
To examine the penetration
profile and fusion of a weld,
macro etching involves:
Figure 3.08.1: Macro etch cross section of an acceptable weld
1. Cutting the sample
through the weld with a
non-thermal process
2. Polishing the surface to
at least a 600-grit finish
3. Applying an etchant,
ammonium persulfate or
diluted hydrochloric acid
4. Visually examining the
cross section of the weld
An acceptable weld (see Figure 3.08.1) will show complete fusion, free of any cracks.
HARDNESS TESTING
The hardness of a weld is affected by:
Composition of the pipe and weld metal
Metallurgical effects of the welding process
Heat treatment
3.08 WELDING PROCEDURES MANUAL Page 2 of 2
OPERATING PROCEDURES
MACRO ETCH AND HARDNESS TESTING OF WELDS
12/31/06
Experience has proven that limitations should be placed on the hardness of the pipe metal, heat-affected zones and weld metal. If too hard, they will not have sufficient ductility for the service conditions, their corrosion resistance may be impaired, or some other factor may dictate this limitation.
This is particularly important for weldments exposed to hydrogen-bearing environments such as sour-crude or sour gas service in pipelines. Increased hardness coupled with hydrogen may cause cracking.
Depending on the application, there are several types of hardness testing machines.
The three most widely used are:
Brinell Hardness
Rockwell Hardness
Vickers Hardness
The hardness testing will be preformed in accordance with ASTM Standard E92. A minimum of five indentations should be made using a Vickers indenter and a 10-kg load in the coarse-grained heat affected zone (HAZ) at the weld toe of each specimen. If the result of this test produces, HAZ hardness values in excess of 350 HV they should be further evaluated for risks of hydrogen cracking.
ACCEPTANCE STANDARDS
The API 1104 acceptance standards applicable to macro etch and hardness testing are contained in Appendix B.
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