Porosity in Castings 4

[JohnsonMadukayil]

Hi friends,

Is there any standard for defining the level of porosity in a casting, on the surface of the castings or on the surface of a finish machined casting/product? It is true that the level of porosity is accepted or rejected as per any particular industrial application and this acceptance criteria may vary from industry to industry.

Thanks
Johnson Madukayil

 

[TVP]

Johnson,

There are many industry standards for evaluating the amount of porosity present in castings. One of the most commonly used methods is radiography. The part to be evaluated is subjected to x-rays, and similar to x-rays of the human body, density differences are highlighted. ASTM 1030, Standard Test Method for Radiographic Examination of Metallic Castings is a general standard for this method, which then references a set of Reference Radiographs for various levels of porosity. These Reference Radiographs are actual x-ray film images of various castings defects. There are several different sets of Reference Radiographs, depending on material, product form, etc. For example, Al & Mg castings are covered by ASTM E 155, while Ductile Iron is covered by ASTM E 689. Thin-wall steel castings are covered in ASTM E 446 and heavy-wall steel castings in ASTM E 186.

You may want to consult some reference books for more information on this topic. AFS (American Foundry Society,

http://www.afsinc.org)

has three books I recommend you review:

Casting Defects Handbook

Analysis of Casting Defects

International Atlas of Casting Defects

ASM International (

http://www.asminternational.org)

also has some excellent references on this subject:

ASM HANDBOOK Volume 5, Castings
ASM HANDBOOK Volume 17, Nondestructive Evaluation and Quality Control

 

[Hush]

MSS SP55 covers visual inspection of valve castings. We use this for all pressure containing castings.

 

Concur with the previous two correspondents. Problem is - it is not a B&W science. There is a degree of subjective aqssessment. Hope that you are not taking on a casting supplier! They know every wrinkle!!!

 

[bruv]

Johnson,

I work in the foundry industry, and we are subjected to a wide range of surface finish specs - the most common are MSS SP55 and also ASTM A802. If memory serves me correctly (I'm at home at the moment) both of these refer to surface comparator plates.

TVP is corect when he says that radiography is good for detecting porosity in castings. However, it is more suited to finding sub-surface defects. Better techniques for finding surface defects are Magnetic Particle Inspection (MPI) or Liquid Penetrant Inspection (LPI). MPI works only with magnetic materials. LPI can be used on almost any material. I don't know any of the MPI specs, but typically our customers ask for LPI to ASME 8 DIV 1 Appendix 7, or they generate their own requirements. These specs define the maximum size, shape and quantity of any permissible defects.

Best of luck

 

[CoryPad]

What is MSS SP55?

 

[mloew]

CoryPad,

MSS SP 55 :
QUALITY STANDARD FOR STEEL CASTINGS FOR VALVES, FLANGES AND FITTINGS AND OTHER PIPING COMPONENTS - VISUAL METHOD FOR EVALUATION OF SURFACE IRREGULARITIES

Gives series of reference photographs of surface irregularities common to steel pressure castings and illustrations of generally acceptable and rejectable quality.

Equiv. Std.: None Advised
Publisher: MSS:MANUFACTURERS STANDARDIZATION SOCIETY
127 PARK STREET N.E.
VIENNA
VIRGINIA 22180
U.S.A.

http://www.mss-hq.com

Contents:
Terms and Conditions
Foreword
Table of Contents
1 Scope
2 Definition of Surface Quality by Visual
Inspection
3 Reference Photographs
4 Terminologies for Reference Photographs
5 Comparison of MSS SP-55 Acceptance Criteria
with Scrata Standard Covering Surface Texture
Quality Standards
Table 1 Acceptance Levels in the Scrata Comparators
Considered Equivalent to the Acceptance
Criteria of MSS SP-55
Annex A Reference Standards Applicable Dates
Photographs
Best regards,

Matthew Ian Loew

 

[mloew]

Bruv,

Just a note:

ASTM A 802: PRACTICE FOR STEEL CASTINGS, TEXTURES AND DISCONTINUITIES, EVALUATION AND SPECIFYING, BY VISUAL EXAMINATION has been superseded by:

ASTM A 802/A802M:
Standard Practice for Steel Castings, Surface Acceptance Standards, Visual Examination



Best regards,

Matthew Ian Loew