Incident NH3 09-001: Rupture rubber hose transferring Anhydrous NH3 service

Introduction:
On July 15, 2009, a transfer hose ruptured while transferring anhydrous ammonia from a cargo tank truck to a storage tank at a distribution and processing facility in Swansea, South Carolina, USA. A white cloud of toxic anhydrous ammonia gas traveled from the facility across a highway. A motorist traveling on the highway at the time drove into the ammonia cloud, exited the vehicle, and was killed as a result of inhaling the gas. Additionally, seven people were hospitalized for respiratory issues.
The 18-foot-long ruptured transfer hose was manufactured by Durodyne, Inc., in 2005 and was marked for use with liquefied petroleum gas (LPG) as product number DD-G-220. The hose was intended for the conveyance of LPG products in production or delivery. The hose is constructed of nitrile rubber reinforced with textile braids and covered with perforated chloroprene rubber. The nominal inner diameter of the hose is 2.00 in. and the nominal outer diameter is 2.74 in. It was rated for use between 40 8F and 180 8F. The hose was Underwriters Laboratories Incorporated (UL) approved and was certified to meet the UL 21 standard for LPG hose [2,3]. The maximum allowable operating pressure of the hose was 350 psig and the minimum hydrostatic burst strength was 1750 psig, in accordance with UL 21.
From 2006 until mid-May 2009, the ruptured hose was used to transfer LPG an unknown number of times. From mid-May 2009 until the rupture on July 15, 2009, the operator estimated that the hose transferred anhydrous ammonia 2–12 times.

Conclusions:
The micro FTIR spectra confirm that the PET fibers in first and second braid layers of the ruptured hose are chemically degraded to ammonium salts of terephthalic acid (ammonolysis).
Optical microscopy reveals that the reinforcing fibers in the first and second braid layers are mechanically degraded such that they are brittle.
Optical fractography indicates that the hose rupture initiated on the inside surface of the hose and propagated toward the exterior and longitudinally along the hose.
The loss in mechanical properties of the first and second reinforcing layers reduced the maximum allowable pressure of the hose below the operating pressure experienced during an ammonia transfer, causing the hose to rupture.

Refer to our Incident Databases:

Incident NH3 09-001: Rupture rubber hose in anhydrous ammonia services

and our E-Library for the complete story:

2012 Budinski Failure analysis of a rubber hose in anhydrous ammonia service

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