1、Lessons Learned Entry: 0606Lesson Info:a71 Lesson Number: 0606a71 Lesson Date: 1998-12-10a71 Submitting Organization: WSTFa71 Submitted by: Jan JungewaelterSubject: High Pressure Steam Strainer Failure Description of Driving Event: A four inch-diameter cast iron strainer in a 225 psig steam line fai
2、led catastrophically, releasing high pressure steam and hurling strainer pieces and attached parts in the equipment building. The steam and projectiles weighing up to 50 lbs. posed life-threatening hazards; however, they caused only minor damage to the steam piping and surrounding equipment. Two emp
3、loyees opening a steam supply valve nearby were not injured.The failure was caused largely by the inappropriate use of material for the strainer. The strainer was manufactured from gray cast iron to ASTM Specification A 126 Class B. A stress analysis was performed by the A&E contractor assuming cast
4、 steel construction. The principle stress at the strainer position would not exceed the maximum allowable stress for steel but would for cast iron, as specified in ASME B31.1 (1995 edition). Repeated water hammer effects during operations hastened eventual strainer failure.Upon acceptance of the str
5、ainer, material criticality associated with analysis was not recognized as a determining factor in component acceptability. Operating and performance parameters (pressure and temperature) were the principle considerations.Also, the hazard analysis did not address steam line rupture resulting from st
6、eam flashing or water hammer. It is common within NASA and industry to dismiss catastrophic failure potential of ASME code-compliant pressure systems as non-credible, given intrinsic safety factors. Procedural problems combined with some malfunctioning steam traps caused the part to be subjected to
7、significant water hammer during system startup. Employees were not instructed explicitly in how to recognize water hammer symptoms.Lesson(s) Learned: Provided by IHSNot for Resale-,-,-Careful consideration of the effects of failure must be made before using cast iron parts in steam systems.Employees
8、 should be trained and prepared to recognize symptoms of unique hazards. If conditions like water hammer are significant operational concerns, procedures and personnel training should specifically address how to recognize (look/listen for) the warning signs.In contracting, be careful of “slimming do
9、wn“ technical specifications for performance-based results.Recommendation(s): Assess the use of materials in steam systems to ensure that they are not subjected to stresses in excess of the allowable. Ensure that the effects of catastrophic failure due to non-ductile materials, like cast iron, are c
10、onsidered.Ensure performance-based specifications are sufficiently detailed to address all allowable stresses, including operating conditions. Identify potential hazards associated with material substitution.Ensure employees can recognize warning signs of hazards unique to a system.Evidence of Recur
11、rence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Facilitiesa71 Parts Materials & Processesa71 Pressure Vesselsa71 Safety & Mission AssuranceAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHSApproval Info: a71 Approval Date: 1998-12-10a71 Approval Name: Jan Jungewaeltera71 Approval Organization: NT4a71 Approval Phone Number: 505-524-5161Provided by IHSNot for Resale-,-,-
