API PUBL 938-A-1996

$47.45

An Experimental Study of Causes and Repair of Cracking of 1 1/4 Cr- 1/2 Mo Steel Equipment

Published By	Publication Date	Number of Pages
API	1996	222

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Description

The origin of this project was a n in-depth study for API of numerous reported incidents of cracking of equipment of l Cr- ¹/₂Mo and 1 ¹/₄Cr- ¹/₂Mo-Si steels, The report to API is an explanation of the problem and the basis for further work to help prevent and repair such cracking. Metallurgical reports, fabrication records and service histories were reviewed. Worldwide research on the subject by steelmakers and studies of these alloys and similar materials in related applications were considered. In many cases, the cracking was major and cracks propagated in service. Emphasis in the report was placed on the causes of crack initiation during fabrication or of their appearance after only a short time in service.

I t was concluded that major contributions to the cracking were from poor design, fabrication and operating practices which should be corrected using reasonable precautions and well known technology. Such action would pre- vent future vessels from entering service with preexisting cracks or initiating cracks in service. However, there was strong evidence that some of the plates and forgings used for vessel construction were more prone to cracking than others or have disturbingly low toughness. This study was intended to recommend ways to eliminate detrimental fabrication practices and materials.

Fabrication and repair operations must be upgraded because subsurface cracks which cannot be readily detected may occur and then emerge in service. Repairs have been troublesome.

Specifically, the study was developed to address the materials, fabrication and repair issues of greatest concern.

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