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CLASSIFICATION SYSTEM NUMBER 514937

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Flight deck refuelling hose failure HMCS Preserver

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FLIGHT DECK REFUELLING HOSE FAILURE HMCS PRESERVER

J.A. Hiltz - V. Roy- J.R. Matthews

Copy No.ls

DEFENCE RESEARCH ESTABLISHMENT ATLANTIC

••• National Defense Defence nationale

Technical Memorandum

DREA TM 2000-022

January 2000

Canada

P514937.PDF [Page: 4 of 41]-

I+ National Defence Research and Development Branch

Defense nationale Bureau de recherche et devetoppement

OREA TM 2000·022

FLIGHT DECK REFUELLING HOSE FAILURE

HMCS PRESERVER

J.A. Hiltz - V. Roy- J.R. Matthews

DEFENCE RESEARCH ESTABLISHMENT ATLANTIC PO Box 1012, Dartmouth

Nova Scotia, Canada B2Y 3Z7

Approved by ./. ~~~ R.M. Morchat,

Head/ Dockyard Laboratory

January 2000

TECHNICAL MEMORANDUM

Canada

Defence Research Establishment Atlantic

Prepared by

Centre de Recherches pour la Defense Atlantique

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ABSTRACT The results of an investigation of a flight deck refuelling hose on HMCS Preserver that failed during a fuel recirculation step are reported. Markings on the hose indicated that it was manufactured by Titan and conformed to Military Specification MIL-H-6615E "Hose Assemblies, Rubber, Fuel and Water, With Reattachable Couplings, Low Temperature". MIL-H-6615E specifies physical, chemical and mechanical properties for hose and these were used as a basis for the investigation. Chemical analysis indicated that the inner tube and outer cover of the hose were as specified. However, a good length of the failed hose and an unused length of hose from the same batch failed a proof pressure test that required they withstand pressurization to 275 psi for 30 seconds. The adhesion of one of the two layers of reinforcing fibres to the rubber portion of the hose was also less than that specified. The mechanical responses of fibres from the inner and outer layers of reinforcement were also different. As part of the failure investigation, the same analyses were made on a length of refuelling hose from a different manufacturer. This material met the requirements for MIL-H-6615E hoses.

It was concluded that the Titan hose failure was related to the fibre reinforcement. Poor adhesion of the inner fibre reinforcing layer and differences in the mechanical properties of the fibres from the inner and outer reinforcing layers are possible causes. As only one batch of Titan hose was tested, it was not possible to determine if this is confined to this batch of hose or whether it is indicative of a more general problem resulting from the manufacturing process.

RESUME Les resultats d'une enquete sur la defaillance d'un tuyau de ravitaillement du pont d'envol du NCSM Preserver pendant une operation de recirculation sont maintenant connus. D' apres les marques inscrites sur le tuyau, celui-ci etait fabrique par Titan et Conforme a la specification mihtaire MIL-H-6615E ··Hose Assemblies, Rubber, Fuel and Water, Re­attachable Couplings, Low Temperature... La MIL-H-6615E specifie les proprietes physique, chimiques et mecan1ques des tuyaux. Ces proprietes ont servi de point de depart a l' enquete. L' analyse chimique a indique que le tube interne et l' enveloppe externe etaient conformes a la specification. Cependant, une longueur importante du tuyau def aillant et une longueur inutilisee de tuyau du meme lot n'a pas reussi un test qui exigeait de resister a 275 lb/po2 pendant 30 secondes. L'adherence de l'une des deux couches de renfort en fibres a la surface de caoutchouc etait egalement inferieure a la valeur prescrite. La reponse mecanique des fibres de la couche interieure et de la couche exterieure de renfort etait aussi differente. Dans le cadre de l 'enquete, on a effectue la meme analyse sur une longueur de tuyau de ravitaillement d'un autre fabricant. Le materiau repondait aux exigences de la specification MIL-H-6615E.

On en a conclu que la defaillance du tuyau de Titan etait liee aux fibres de renfort. Une mauvaise adherence de la couche interne de renfort en fibres et des differences dans les proprietes mecaniques des couches interne et exteme de renfort sont des causes possibles. Comme on a mis a l' essai un seul lot de Titan, il n' a pas ete possible de determiner si ce lot etait le seul implique et ou si c'etait !'indication d'un probleme plus general resultant d'un procede de fabrication.

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Flight Deck Refuelling Hose Failure HMCS Preserver

.John A. Hiltz, Vincent Roy. and .James R. Matthews

EXECUTIVE SUMMARY

Introduction

A flight deck refuelling hose on HMCS Preserver failed during a fuel recirculation step in the Fall of 1999. As these hoses carry 3-GP-24 aviation turbine fuel, the failure represents a significant safety and fire hazard. DREA was asked to participate in the investigation of the refuelling hose failure. Markings on the hose indicated that it was manufactured by Titan and conformed to Military Specification MIL-H-6615E "Hose Assemblies, Rubber, Fuel and Water, With Reattachable Couplings, Low Temperature". MIL-H-6615E specifies physical, chemical and mechanical properties for hose and these were used as a basis for the investigation.

Principal Results

Chemical analysis indicated that the inner tube (poly(butadiene-acrylonitrile) rubber) and outer cover of the hose (poly( chloroprene and poly(butadiene-acrylonitrile) rubber mixture) conformed to MIL-H6615E. However, further testing of the hose indicated it did not meet MIL-H-6615E specifications. A good length of the failed hose and an unused length of hose from the same batch failed a proof pressure test that required they withstand pressurization to 275 psi for 30 seconds. The adhesion of one of the two layers of reinforcing fibres to the rubber portion of the hose was also less than that specified. In addition, the mechanical responses of the inner and outer reinforcing fibres were significantly different. Proof pressure testing of a length of hose from another manufacturer material met the MIL-H-66 l 5E requirement. It was concluded that the Titan hose failure was related to the fibre reinforcement. Poor adhesion of the inner fibre reinforcing layer and differences in the mechanical properties of the fibres from the inner and outer reinforcing layers are possible causes. The failed Titan hose had not been proof tested prior to service on HMCS Preserver. MIL-H-661 SE requires that a length of hose from each batch of hose be proof pressure tested prior to use.

Significance of the Results

The most significant finding was that a batch of hose labelled as conforming to a military specification did not meet the requirements of the specification. Also the failure of a length of hose that had not been proof tested illustrates the importance of proof testing of refueiling hoses. As only one batch of Titan hose was tested, it is not possible to determine the problems found with this batch of hose are an anomaly or if they are indicative of a more general problem resulting from the manufacturing process.

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CRDA TM-2000-022

Defaillance du tuyau de ravitaillernent du pont d'envol du NCSM Preserver

John A.Hiltz, Vincent Roy et James R. Matthews

RESUME

Introduction

Un tuyau de ravitaillement sur le pont d'envol du NCSM Preserver s'est rompu a l' automne 1999 pendant une operation de recirculation du carburant. Comme ces tuyaux acheminent du carburant pour turbines aeronautiques 3-GP-24, leur rupture pose un probleme important de securite avec risque d'incendie. On a demande au CRDA de part1ciper a I' enquete sur cette defaillance. D'apres les marques, le tuyau etait fabrique par Titan et etait Conforme a la specification militaire MIL-H-6615E "Hose Assemblies, Rubber, Fuel and Water, With Re-attachable Couplings, Low Temperature· . Cette specification, qui prescrit des proprietes physiques, chimiques et mecaniques, a servi de point de depart a I' enquete

ResuJtats principaux

L'analyse chimique a revele que le poly(butadyene-acrylonitrile) du tube interne et le melange de poly(chloroprene) et de poly(butadyene-acrylonitryle) de l'enveloppe externe etaient conformes a la specification MIL-H-6615£. Toutefois, apres d'autres essais, il s'est avere que le tuyau n'etait pas conforme a la specification en question. Une bonne longueur de tuyau rompu et une longueur non utilisee de tuyau du meme lot n'ont pas reussi une epreuve depression exigeant de resister a 275 lb/po2 pendant 30 s. De plus, !'adherence d'une des couches de renfort en fibres sur la surface de caoutchouc etait inferieure a la valeur prescrite et les reponses mecaniques des renforts interne et externe differaient. Un essai de pression effectue sur une longueur de tuyau d'un autre fabricant a montre qu'il etait Conforme a la specification MIL-H-6615£. On en a conclu que la defaillance du tuyau Titan provenait du renfort de fibres. Une mauvaise adherence de la couche interne, des propnetes mecaniques differentes entre couche interne et externe sont des causes possibles. De plus, le tuyau Titan n'avait pas subi d'essai avant sa rmse en service sur le Preserver comme la specification MIL-H-6615E l' exige pour chaque lot.

Importance des resultats

La constatation la plus importante a ete qu'un lot etiquete Conforme a une specification militaire ne repondait pas aux exigences de cette specification. La defaillance d'une longueur de tuyau qui n'avait pas subi d'essai illustre l'importance des essais pour les tuyaux de ravitaillement. Comme un seul lot de tuyaux Titan a ete mis a l'essai, il est impossible de dire si le probleme constate est une anomalie ou s'il denote un phenomene plus general du a un procede de fabrication.

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Table of Contents

Abstract Executive Summary Table of Contents

Introduction

Hose Materials Titan Hose German Hose

Failed Titan Hose Physical Characteristics

Chemical Analysis Py-GC/MS Instrumentation and Experimental Conditions Failed Titan Hose New Titan Hose German Hose

Proof Tests Failed Titan Hose New Titan Hose German Hose

Mechanical Testing of Hose Materials Testing Machine Hose and Reinforcing Fibre Specimen Preparation Tensile Tests Results

Summary

Conclusions

References

List of Figures

Figures

Intact Hose Specimens Outer Cover and Inner Tube Reinforcing Fibres Rubber/Reinforcing Fibre Adhesion

v

Page

ii iii v

1

1 1 2

2 2

4 4 4 5 5 6

6 6 7 7

7 7 8 8 8 9 9 10

11

12

13

14

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Introduction

DREA Dockyard Laboratory was requested by the Mechanical Engineering Section,

FMF Cape Scott, to aid in the investigation of a failed refuelling hose (Nato Stock

Number 4720-21-856-9545, Hose Nonmetallic, Synthetic Rubber). Labelling on the hose

indicated that it was manufactured by Titan. The hose was part of the flight deck aviation

fuel (Nato Code F44) delivery system on HMCS Preserver. A schematic of the system is

shown in Figure 1. It was reported that the hose was used in a fuel recirculation step

prior to delivery of fuel to an aircraft.

In the course of the investigation of the failure, the undamaged length of the failed Titan

hose, an unused length of Titan hose from the same batch as the failed hose, and a length

of hose from a different manufacturer were proof tested at 275 psi. The failed and

unused lengths of Titan refuelling hose failed the proof pressure test. The hose from the

other manufacturer passed the proof pressure test.

This report summarizes the results of the investigation of the physical, chemical and

mechanical properties of the refuelling hoses.

Hose Materials

Titan Hose

The failed refueling hose was labelled MIL-H-6615Effype 1/2Q98/SP0770-98-

MYN62ffitan. Military Specification MIL-H-6615E "Hose Assemblies, Rubber, Fuel

and Water, With Reattachable Couplings, Low Temperature"[l] requires that hose

conforming to this specification be labeled MIL-H-6615E -Type (1or2 as applicable) -

date of manufacture (quarter and year)- and manufacturer's name or trademark. Type 1

hoses contain an electrical bond whereas Type 2 hoses do not. The label on the failed

hose indicates that it contains an electrical bond and was manufactured in the second

quarter of 1998 (2Q98) by Titan. SP0770-98-MYN62 most likely refers to a

batch/production number.

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Military Specification MIL-H-6615E requires that the hose consist of a compounded

inner tube, braided, loomed, or plied reinforcement, spirally wound electrical bonding

wires, and a compounded cover. The inner tube and outer cover of the hose must be

composed of an extruded high aromatic aviation fuel-resistant synthetic elastomer and

poly(chloroprene) rubber respectively. The inner tube and outer cover must be at least

1/16 inch thick. The spirally wound electrical bonding wires are required to make an

angle of not less than 45 degrees with the longitudinal axis of the hose and, for a braided

wire, have an area equivalent to 48 strands 36 B&S gauge.

There are a number of performance specifications for MIL-H-6615E hoses. One of these

is a proof pressure test at 275 psi for 30 seconds. It was reported by the Mechanical

Engineering Section FMF Cape Scott that the failed Titan hose had not been proof tested

prior to service on HMCS Preserver[2].

German Hose

The refueling hose from a different manufacturer was labeled "Made in Germany,

Aircraft Refueling Hose Low Temperature TVP, 450 psi test pressure, 300 psi design

working pressure, 6305630/2, 05/1999". This is referred to as the 'German' hose in this

report.

Failed Titan Hose

The failed section of hose is shown in Figure 2. The failure penetrated the hose, that is

both the inner tube and cover were split over a distance of approximately 6 inches and the

reinforcing fibres were broken. One end of the failure surface approached to within

approximately 2 inches of the coupling. Figure 3 shows an expanded view of the failure

surface on the exterior of the hose.

Physical Characteristics

Measurement of the hose indicated that the inside diameter was 2.0 inches and therefore

had a MIL-H-661 SE size code "C".

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A length of hose was dissected to determine if it met MIL-H-6615E requirements for

construction. The specification requires that inner tube be greater than 0.0626 (1116)

inches thick. Measurements of the inner tube of the failed hose indicated that it was

greater than 0.090 inches thick. However, the thickness varied from one area to another.

The reinforcement consisted of two plies of reinforcing fibres oriented at approximately

90 degrees to one another. Both plies of reinforcing fibres were oriented at greater than

45 degrees to the longitudinal axis of the hose. The fibres were not uniformly distributed

around the circumference of the hose and a thin rubber layer separated the reinforcing

plies.

The reinforcing fibres could be pulled away from the inner tube or outer cover easily.

The inner tube and outer cover after removal of the reinforcing plies are shown in Figure

4a. It can be seen that the plies crune away from the inner tube more cleanly than from

the outer cover. There was also a significant difference in the appearance of the inner

and outer plies of reinforcing fibres when they were separated from the inner tube and

outer cover of the hose respectively. The inner plies were string-like while the outer plies

were looser and did not appear to be twisted as much as the inner plies. Exrunples of the

inner and outer reinforcing plies are shown in Figure 4b.

17 .5 cm lengths of the inner and outer plies were weighed and the inner plies were

heavier than the outer plies (0.135 g versus 0.130 g). This may be due to the runount of

outer ply material that was lost when the plies were removed from the hose.

An electrical bonding wire (36 strands) was braided around one of the reinforcing fibers.

The bonding wire was located in the reinforcing layer toward the exterior of the hose.

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Chemical Analysis

Py-GC/MS

The outer rubber cover, inner rubber tube, and the reinforcing fibres of the hose samples

were analysed using pyrolysis gas chromatography/mass spectrometry (py-GC/MS).

This technique identifies polymeric materials on the basis of their pyrolytic (high

temperature, inert atmosphere) degradation products.

Instrumentation and Experimental Conditions

All pyrolyses were performed using a CDS Model 122 pyroprobe controller and a

platinum coil pyroprobe (Chemical Data Systems, Oxford, PA). The sample (0.1 mg to

0.2 mg) was centered with glass wool in a 25 mm quartz tube and heated with the ramp

off (maximum heating rate) to the final temperature (700 °C). The hold time at the final

temperature was 20 seconds.

GC/MS analysis was carried out on a Fisons Platform II quadrupole GC/MS with a

Fisons Model 8000 GC. The pyrolysis products were separated on a 30 m long X 0.25

mm inside diameter ARX-5 capillary column with a 0.25 µm thick stationary phase (5%

phenyl-95%dimethylpolysiloxane). The GC was operated in the constant pressure mode

(10 psi) using Helium as the carrier gas. The GC oven was programmed to hold at 40 °C

for 4 minutes, then increase to 300 °C at a rate of 10 °C/min, and finally held at 300 °C

for 10 minutes. The total run time was 40 minutes.

The quadrupole MS was operated in the full scan mode between 25 atomic mass units

(amu) and 500 amu. The scan rate was 1 scan per second. Data acquisition and

manipulation was performed on a MassLynx data system containing the NIST library of

mass spectra ( -65,000 entries).

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Failed Titan Hose

Pyrograms of the outer rubber cover, the exterior of the outer rubber cover, and the inner

rubber tube are shown in Figure 5. Comparison of the pyrograms indicates that the

rubbers giving rise to these chromatograms are similar. Mass spectral analysis of the

peaks indicates that the pyrolysis products include the dimer of butadiene,

ethenylcyclohexene, at 6.23 minutes in Figure Sa, and several peaks characteristic of the

pyrolytic degradation of poly(butadiene-acrylonitrile) rubber at 8.60 minutes, 10.10

minutes, 10.79 minutes, and 15.43 minutes. These compounds have molecular weights

of 93, 103, 107 and 160 respectively.

The pyrograms of the outer rubber cover (Figures Sa and Sb ) also contained 1-chloro-4-

( 1-chloroethen y I )cyclohexene ( -14.80 minutes). 1-chloro-4-( 1-

chloroethen yl )cyclohexene is the dimer of the monomeric unit of poly(chloroprene)

rubber and is the major pyrolytic degradation product of poly(chloroprene) rubber. No

evidence of poly( chloroprene) rubber was found in the sample from the inner tube.

The pyrogram of the reinforcing material is shown in Figure 6a. Analysis of the

pyrolysis degradation products indicated that the fibres were composed of poly( ethylene

terephthalate) or PET. A pyrogram of a standard sample of PET is shown in Figure 6b.

New Titan Hose

The analysis of the outer cover, inner tube and reinforcing fibres were repeated for

another length of Titan MIL-H-6615E hose taken from stores. The markings on this hose

indicated that it was from the same batch of hose as the failed refueling hose from HMCS

Preserver. The pyrograms of the outer cover, inner tube, and reinforcing fibre are shown

in Figures 7a through 9a respectively. For comparison the pyrograms of the

corresponding material from the hose failed in service are shown in the Figures 7b

through 9b. The similarity of the pyrograms of the outer cover, inner tube and

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reinforcing fibres from the two lengths of Titan hose indicate that the rubbers and

reinforcing fibres used in the two lengths of hose are the same.

German Hose

Pyrograms of the outer cover and inner tube of the 'German' hose are shown in Figure

10.

The major pyrolytic degradation product of the outer cover was 1-chloro-4-

( chloroethenyl)cyclohexene (14.75 minutes), which is the dimer of the monomeric unit of

poly(chloroprene). The monomer of poly(chloroprene), 2-chlorobutadiene (2.12

minutes), was also found in the degradation products. These degradation products are

characteristic of poly(chloroprene) rubber.

Mass spectral analysis of the pyrolytic degradation products of the inner tube indicated it

was poly(butadiene-acrylonitrile) rubber. Characteristic peaks were the dimer of

butadiene (6.23 minutes), and compounds with molecular weights 93 (8.60 minutes), 103

(10.07 minutes), 107 (10.75 minutes) and 160 (15.49 minutes).

The pyrogram of the reinforcing fibre is shown in Figure 11 a. Analysis of the pyrolytic

degradation products of the reinforcing fibres indicated that they were consistent with a

cellulose-based fibre similar to cotton. The pyrogram of a sample of cotton is shown in

Figure I lb for comparison. Levoglucosan (1,6-anhydro-beta-D-glucopyranose) (19.39

minutes in Figure 1 la), a major degradation product of cotton, is found in both

pyrograms.

Proof Tests (275psi)

Failed Titan Hose

The unfailed portion of the refuelling hose was proof tested at the Pipe Shop, Building D-

165, Formation Halifax. The unfailed portion of the refueling hose was 58 ft 2 in long at

0 psi and 58 ft 1 inch when subjected to a hydrostatic pressure of 10 psi. The hose failed

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catastophically just as the hydrostatic pressure reached 275 psi. Military specification

MIL-H-6615E required that the hose, when subjected to a hydrostatic pressure of 275 psi,

not leak or show imperfections for not less than 30 seconds.

The hose failed 7 ft 10 in from one coupling and 50 ft 3 in from the other coupling. The

failed hose is shown in Figure 12.

New Titan Hose

Following the failure of the 'good' section of failed refueling hose, another length (60

feet) of refueling hose was drawn from stores and tested. The markings on this leJ.lgth of

hose were identical to those on the hose that failed on HMCS Preserver. This indicates

that they were taken from the same batch (lot) of hose.

The test plan for this section of hose included cycling the hose pressure from 10 psi to

150 psi twice, then from 10 psi to 200 psi once, from 10 psi to 250 psi once, and finally

from 10 psi to 275 psi. The hose failed catastrophically at 240 psi during the

pressurization from 10 psi to 250 psi. The failure was located adjacent to the coupling at

one end of the hose. The failure initiation site appeared to be approximately 3 inches

from the coupling and the failure ran back to the coupling.

'German' Hose

A length of the 'German' hose was proof tested at 275 psi and passed.

Mechanical Testing of Hose Materials

Testing Machine

Tensile testing was done on an Instron model 8801 tensile testing machine using a grip

separation rate of 1 inch/minute. This Instron tensile testing machine has a stroke of 6

inches and a load limit of 22000 lbf. The adjustable hydraulic grips were set to the lowest

pressure setting to prevent crushing the rubber.

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Hose and Reinforcing Fibre Specimen Preparation

Rings (approximately 0.75 inches in width) were cut from each fuel hose in order to

make tensile specimens (see Figure 13). For each hose type, three tensile tests were

performed. One on the intact piece of hose (outer cover, reinforcing fibres and and inner

tube), one on the outer cover, and one on the inner tube.

Reinforcing fibre test specimens were taken from a length of hose. This required

separation of the inner tube and outer cover from the fibres.

Tensile Tests Results

Intact Hose Specimens

The plots of stress versus elongation for the intact tensile specimens from the Titan and

German refueling hoses are shown in Figure 14. It is apparent from the plots that the

Titan and German hoses are different. The Titan fuel hose did not break during the test

and both loading and unloading curves are found in the figure. The maximum stress at

230% elongation was approximately 300 psi. As the Titan tensile specimen did not

rupture during the test, 230% elongation is not the limit for the Titan tensile test

specimens. The maximum elongation (230%) of the specimens was limited by the stroke

of the Instron Model 8801 testing machine (6 inch maximum) and the initial sample

gauge length of 2.3 inches.

In contrast to this the German hose began to fail at 40% elongation and supported a

maximum stress of 1500 psi at that elongation. The failure of the German hose could be

followed during the tensile test. The failure initiated with the rupture of the reinforcing

fibres when the stress reached 1500 psi. As the fibers ruptured and separated, the load

supported by the specimen dropped rapidly. The outer cover could not sustain the load

and began to rip slowly. The load supported by the specimen continued to drop and was

transferred to the inner tube. Initially the inner tube was loaded over a short portion

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where the outer cover had ruptured. The tube then slowly separated from the cover. The

separation process can be seen as small variations in the load at elongations above 50%.

The inner tube failed at 225% elongation. It is not believed that this separation of the

cover from the tube would occur if the fuel hose were in use.

Outer Cover and Inner Tube

Plots of stress versus elongation for tensile specimens taken from the outer cover and

inner tube of the Titan hose, and the inner tube of the German hose are shown in Figure

15. The slopes of the stress versus strain plots indicate that the inner tube from the

German hose has a slightly larger modulus of elasticity than the inner tube of the failed

hose. The German inner tube reached a stress of 630 psi at 230% elongation while the

inner tube and outer cover of the failed hose reached stresses of 440 psi at 230%

elongation.

The tensile test result for the outer cover of the German hose is shown in Figure 16. This

was plotted separately because it was not possible to separate the outer layer of

reinforcing fibres from the outer cover. It can be seen in Figure 16 that the reinforcing

fibres had a significant effect on the performance of the sample, i.e., the maximum stress

increased to 1200 psi and the sample failed at 34% elongation.

Reinforcing Fibres

Two layers of reinforcing fibres were present in the Titan hose. Individual fibres from

the inner and outer layers of reinforcement are refered to as the inner and outer fibres.

Plots of load versus stroke for individual fibres from the Titan fuel hose are shown in

Figure 17. The initial slopes and therefore moduli of the inner and outer fibres are the

same. Also the slopes of the plots of Joad versus stroke for the inner and outer fibres as

they are unloaded are the same.

Although the inner and outer fibres have similar properties for strokes up to 0.1 inch, the

maximum load supported by the outer fibres is less than half the maximum load

supported by the inner fibres.

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The inner and outer fibres are shown in Figure 4. It can be seen that the outer fibres

sustained some damage in separating them from the hose. To determine if this was

responsible for the difference in the load/stroke response of the inner and outer fibres, the

inner fibres were manipulated in an attempt to reproduce the damage to the outer fibres.

Two things were tried, untwisting or unraveling the fibres and removing some of the fibre

to reduce its weight.

The load/stroke results for the unraveled inner fibre are shown in Figure 17. The effect

of unraveling the inner fibre was small but measurable. However, unraveling did not lead

to a load/stroke curve similar to that for the outer fibres. The inner fibres weighed

approximately 5% more than the same length of outer fibres. To reduce their weight, the

inner fibres were wrapped with tape and the tape removed. This reduced the weight per

unit length of the fibres by 5%. The load/stroke curve for this fibre is also shown in

Figure 17. This treatment had no affect on the peak load but did result in a change in the

slope of the load/stroke curve as it was unloaded.

As neither unraveling nor reducing the weight of the inner fibre by 5% resulted in a

load/stroke response similar to the outer fibre from the failed hose, this suggests one of

three things. These are; the inner and outer fibres were different, the outer fibres were

altered during manufacture of the hose, or the outer fibres were damaged during removal

from the hose.

Rubber/Reinforcing Fibre Adhesion

A plot of the load per lineal inch to separate the inner and outer reinforcing fibres from

the remainder of the hose is shown in Figure 18. Specifications for a MIL-H6615E

refueling hose require that the load required to separate the reinforcing fibres from the

rubber hose material be at least 12 pounds per lineal inch. Figure 18 indicates that the

outer fibres were bonded more strongly to the rubber cover than the inner fibres were to

the rubber inner tube. In fact the strength of the bond between the inner fibres and inner

tube is less than required by the military specification for new hose. The superior

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adhesion of the rubber to the outer fibres may have resulted in damage to the outer fibres

when the fibre tensile test specimens were prepared.

Summary

The thickness of the outer cover and inner tube of the Titan hose was greater than 1/16

inch. However, the thickness of the outer cover and inner tube varied along the hose.

Chemical analysis (py-GC/MS) indicated that the failed Titan hose and Titan hose from

stores were composed of a poly(butadiene-acrylonitrile)/poly(chloroprene) outer cover

and a poly(butadiene-acrylonitrile) inner tube. The military specification MIL-H-6615E

required that the outer over be poly(chloroprene) and the inner tube a fuel resistant

elastomer. Poly(butadiene-acrylonitrile) is a fuel resistant elastomer.

Py-GC/MS analysis of the German hose indicated that it was composed of a

poly(chloroprene) outer cover and a poly(butadiene-acrylonitrile) inner tube.

The Titan hose reinforcement was made from a poly(ethylene terephthalate) based fibre.

The German hose reinforcement was made from a cellulose based fibre similar to cotton.

The failed and unused Titan hoses failed the 275 psi proof test.

The German hose passed the 27 5 psi proof test.

The mechanical properties of the inner and outer reinforcing fibres of the Titan were

different. The peak load sustained by the outer reinforcing fibres was less than one half

that sustained by the inner reinforcing fibres. This could be due to damage resulting from

removing the fibres from the rest of the hose.

The adhesion between the inner rubber tube and reinforcing fibres of the Titan hose was

below that specified by MIL-H-6615E (peel strength at least 12 pounds per lineal inch).

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Conclusions

This report deals with only one batch of Titan hose (SP0770-98-MYN62) made in the

second quarter of 1998. The comments and conclusions are therefore confined to this

batch of Titan hose.

The refuelling hose failed because it could not hold the pressure it was subjected to

during fuel recirculation.

The failed Titan hose did not conform to military specification MIL-H-6615E. Testing of

the failed Titan hose and an unused length of hose from the same batch revealed that they

could not meet the 275 psi proof test requirement for MIL-H-6615E hoses. This

illustrates the importance of proof testing prior to installation of the flight deck refuelling

hoses on CF Ships.

The reinforcing fibres were not uniformly wound around the hose and the adhesion of the

inner layer of reinforcing fibres to the rubber portion of the hose was significantly less

than the adhesion of outer layer of reinforcing fibres to the rubber portion of the hose.

Testing indicates that the adhesion for the inner layer of reinforcing was less than

specified in MIL-H-66 l 5E. The mechanical responses of the inner and outer layers of

reinforcing fibres were also different. These factors may have been responsible for the

failure of the hose.

The ·German' hose, Aircraft Refueling Hose Low Temperature TVP, 450 psi test

pressure, 300 psi design working pressure, 6305630/2", 05/1999, was superior to the

Titan hose and is suitable for use as flight deck refuelling hose.

It is strongly recommended that any hose proposed for flight deck refuelling be proof

tested at 275 psi according to the appropriate procedure.

12

P514937.PDF [Page: 21 of 41]-

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References

1. Military Specification MIL-H-6615E "Hose Assemblies, Rubber, Fuel and Water,

With Reattachable Couplings, Low Temperature", 12 March 1984.

2. Discussions Dr. J. Hiltz, DREA/Lt. F. Allen, Mechanical Engineering Section, FMF

Cape Scott, 2 November 1999.

13

P514937.PDF [Page: 22 of 41]•

List of Figures

Figure 1 - Diagram of the flight deck aviation fuel delivery system HMCS Preserver. Figure 2 - Photograph of the failure in the refueling hose from HMCS Preserver. Note the proximity of the failure to hose coupling. Figure 3 - Close up view of failure shown in Figure 2. Figure 4 - Photographs of the outer cover and inner tube of failed refueling hose. Note the difference in the appearance of surfaces where the reinforcing fibres have been removed. Figure 5 - Pyrograms of a) outer rubber cover, b) the exterior of the outer rubber cover, and c) the inner rubber tube of the failed Titan MIL-H-6615E refueling hose. Figure 6 - Pyrograms of a) reinforcing fibre from failed Titan MIL-H-6615E refueling hose and b) standard sample of poly( ethyleneterephthalate ). Figure 7 - Pyrograms of the outer rubber cover from a) an unused length and b) the failed length of Titan MIL-H-6615E batch SP0770-98-MYN62 refueling hose. Figure 8 - Pyrograms of the inner rubber tube from a) an unused length and b) the failed length of Titan MIL-H-66 lSE batch SP0770-98-MYN62 refueling hose. Figure 9 - Pyrograms of the reinforcing fibre from a) an unused length and b) the failed length of Titan MIL-H-6615E batch SP0770-98-MYN62 refueling hose. Figure 10 - Pyrograms of the outer cover and inner tube of the 'German' hose. Figure 11 - Pyrograms of a) the reinforcing fibres from the 'German' hose and b) a sample of cotton. Figure 12 - Photograph of failed Titan hose after proof testing to 275 psi. Figure 13 - Diagram showing preparation of tensile test specimens from hose samples. Figure 14. Plots of stress versus elongation of the intact tensile specimens from the Titan and German refueling hoses. Figure 15. Plots of stress versus elongation for tensile specimens from the outer cover and inner tube of the Titan hose, and the inner tube of the German hose. Figure 16. Plot of stress versus elongation for tensile specimen from the outer cover of the German hose. This sample had the outer layer of reinforcing material attached. Figure 17. Plots of load versus stroke for fibres from the inner and outer layers of reinforcement from the Titan hose, an unraveled fibre from the inner layer, and a weight reduced inner layer fibre. Figure 18 - Plots of the load per lineal inch to separate the inner and outer reinforcing fibres from the remainder of the Titan hose.

14

T

P514937.PDF [Page: 23 of 41]

x

Flight Deck Deck House Connection

x

Upper Forward Separator

Deck House Connection

Supply

85-90 psi

I ~D ReliefValve

XI

; 1-r><i--'--......---...---__..__,,

Upper Forward Separator Recirculation

~ Failed Section of Hose Recirculation and Return

Figure l - Diagram of the flight deck aviation fuel delivery system HMCS Preserver.

P514937.PDF [Page: 24 of 41]

Figure 2 - Photograph of the failure in the refuelling hose from HMCS Preserver Note the proximity of the failure to hose coupling.

P514937.PDF [Page: 25 of 41]-

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-

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Figure 3 - Close up view of failure shown in Figure 2

P514937.PDF [Page: 26 of 41]I

. . 01.iu •

. ,~.,,...~-"" ~· . '

Figure 4 - a) Refuelling hose inner tube (left) and outer cover (right) after removal of reinforcing fibre plies. b) Reinforcing plies from outer cover (top) and inner tube (bottom)

P514937.P

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[Pag

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Figure 5 - Pyrograms of a) outer rubber cover, b) the exterior of the outer rubber cover, and c) the inner rubber tube of the failed Titan MIL-H-6615E refueling hose.

P514937.P

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Figure 6 - Pyrograms of a) reinforcing fibre from failed Titan MIL-H-6615E refueling hose and b) standard sample of poly( ethylene terephthalate ).

•

P514937.P

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Figure 7 Pyrograms of the outer rubber cover from a) an unused length and b) the failed length of Titan MIL-H-6615E batch SP0770-98-MYN62 refueling hose.

P514937.P

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Figure 8 - Pyrograms of the inner rubber tube from a) an unused length and b) the failed length of Titan MIL-H-6615E batch SP0770-98-MYN62 refueling hose.

P514937.P

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Figure 9 - Pyrograms of the reinforcing fibre from a) an unused length and b) the failed length of Titan MIL-H-6615E batch SP0770-98-MYN62 refueling hose.

P514937.P

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P514937.P

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P514937.PDF [Page: 34 of 41]

Figure 12 - Photograph of failed Titan hose after proof testing at 275 psi.

11

P514937.PDF [Page: 35 of 41]

0.75 in -~-... .... .. ._ __

~----------.~.---------------. f I I I

I

----•~ long axis of hose

l

L-----------•~.----------------

1 Ring cut from hose

0.75 in

t Ring opened to make tensile specimen

Figure 13 - Diagram showing preparation of tensile test specimens from hose samples.

P514937.PDF [Page: 36 of 41]

1600 ~--------------------------,

1400

1200

1000 ·0 S: rn 800 rn

German (Cover+ Tube)

f ;;;

600

400

200 Failed (Cover+ Tube)

0

0 50 100 150 200

Bongatlon{%}

Figure 14. Plots of stress versus elongation of the intact tensile specimens from the Titan and German refueling hoses.

700

600

500

..-. 400 ·u;

.s Ill Ill f 300 Ci)

200

100

0

0 50 100 150 200 250

Bongation(%)

Figure 15. Plots of stress versus elongation for tensile specimens from the outer cover and inner tube of the Titan hose, and the inner tube of the German hose.

: r

P514937.PDF [Page: 37 of 41]-

1400

1200

1000

-c;; 800 .e: fl) Ill 2:! <ii

600

400

200

0

0 10 20 30 40

8ongation(o/~

Figure 16. Plot of stress versus elongation for tensile specimen from the outer cover of the German hose. This sample had the outer layer of reinforcing material attached.

40

35

30

25 z .II:

:;- 20 «I 0 ..J

15

10

5

0

0 0 1

Unravelled Inner Fibers

0.2

Outer Fibers

0.3

Stroke (in)

Weight Reduced by 5"/o(lnner Fibers}

04 0.5

Figure 17. Plots of load versus stroke for fibres from the inner and outer layers of reinforcement from the Titan hose, an unraveled fibre from the inner layer, and a weight reduced inner layer fibre.

P514937.PDF [Page: 38 of 41]

25

c Outer :s g 20 Ill r l'CI

Q. c

15 Cll • ! m c 0 10 'iii Cll

J:. ,, Inner c:(

5

Figure 18 - Plots of the load per lineal inch to separate the inner and outer reinforcing fibres from the remainder of the Titan hose.

P514937.PDF [Page: 39 of 41]

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I

3.

4

5

7

8.

9a

UNCLASSIFIED SECURITY CLASSIFICATION OF FORM

(highest classdicanon of Title. Abstract. Keywords)

DOCUMENT CONTROL DATA (Security classlficatoon of trtle, body of abstract and indexing annotation must be antered when the overall document Is ctasslf1ed)

ORIGINATOR (the name and address of the orgamzatton prepanng the document 2. SECURITY CLASSIFICATION Orgamzattons for whom the document was prepared. e g Estabhshment sponsonng a (overall secunty classtficaooo of the document contractor's report, or taskmg agency, are entered m seen on 8 ) mcludmg special warrung terms 1f apphcable)

Defence Research Establishment Atlantic UNCLASSIFIED PO Box 1012 Dartmouth, Nova Scotia, Canada B2Y 3Z7 TITLE (lhe complete document title as md.Jcated on the title page Its class1ficanon should be md.Jcated by the appropnate abbreviauon (S,C,R or U) m parentheses after the ntle)

Flight Deck Refuelling Hose Failure HMCS Preserver

AUTHORS (Last name. first name, middle ml!lal lfnuhtary, show rank, e g Doe, MaJ John E)

John A. Hiltz, Vincent Roy, and James R. Matthews

DATE OF PUBLICATION (month and year of publtcat1on of 6a NO OFPAGES (total 6b NO OFREFS (total cited document) contammg mfonnanon Include mdocument)

Annexes, Appendices, etc}

January 2000 30 (approx.) 2 DESCRIPTIVE NOTES (the category of the document. e g techrucal report, techmcal note or memorandum If appropnate, enter the type of report, e g mtenm, progress, summary, annual or final Give the mclus1ve dates when a specific reporung penod is covered)

TECHNICAL MEMORANDUM

SPONSORING ACTIVITY (the name of the department project office or laboratory sponsonng the research and development Include address)

Defence Research Establishment Atlantic

PROJECT OR GRANT NO (if appropna1e, the applicable research 9b CONTRACT NO. (If appropnate, the apphcable number under and development project or grant number under which the document was winch the document was wntten) wntten Please specify whether project or grant)

1gh12

10a ORIGINATOR'S DOCUMENT NUMBER (the official document 10b OTHER DOCUMENT NOs (Any other numbers winch may be number by which the document ts 1den11fied by the ongmatmg acuvuy assigned tins document either by the ongmator or by the sponsor ) l111s number musl be umque ro this document )

OREA TM 2000-022 11 DOCUMENT AVAILABILITY (any limitations on further dissemination of the document, other than those imposed

by security classification) ( X ) Unlimited distribution ( ) Defence departments and defence contractors; further distribution only as approved ( ) Defence departments and Canadian defence contractors; further distribution only as approved ( ) Government departments and agencies; further distribution only as approved ( ) Defence departments; further distribution only as approved { ) Other (please specify):

12 DOCUMENT ANNOUNCEMENT (any bnutation to the bibhograplnc announcement of dus document Tius wdl normally correspond to the Document Avallab1h1y (I I) However, where funher dlstnbutlon (beyond the audience specified m (I I) 1s possible, a wuler announcement audience may be selected)

Unlimited

UNCLASSIFIED SECURITY CLASSIFICATION OF FORM

DCD03 2t06/87-M/DREA mod 17 Dec 1997

P514937.PDF [Page: 40 of 41]•

UNCLASSIFIED SECURITY CLASSIFICATION OF FORM

(highest class1fica11on of Tnle. Abstract, Keywords)

13. ABSTRACT (a bnef and factual summary of the document It may also appear elsewhere m the body of the document itself It 1s highly desirable that the abstract of class1f1ed documents be unclassified. Each paragraph of the abstract shall begin with an 1nd1cation of the secunty classlf1cat1on of the information m the paragraph (unless the document itself 1s unclassifted) represented as (S). {C), (R), or (U) It 1s not necessary to mclude here abstracts m both o!f1c1al languages unless the text 1s bilingual)

he results of an investigation of a flight deck refuelling hose on HMCS Preserver that failed uring a fuel recirculation step are reported. Markings on the hose indicated that it was anufactured by Titan and conformed to Military Specification MIL-H-6615E "Hose ssemblies, Rubber, Fuel and Water, With Reattachable Couplings, Low Temperature".

-H-6615E specifies physical, chemical and mechanical properties for hose and these ere used as a basis for the investigation. Chemical analysis indicated that the inner tube an uter cover of the hose were as specified. However, a good length of the failed hose and an nused length of hose from the same batch failed a proof pressure test that required they ithstand pressurization to 275 psi for 30 seconds. The adhesion of one of the two layers of

einforcing fibres to the rubber portion of the hose was also less than that specified. The echanical responses of fibres from the inner and outer layers of reinforcement were also

ifferent. As part of the failure investigation, the same analyses were made on a length of efuelling hose from a different manufacturer. This material met the requirements for MIL­-6615E hoses.

twas concluded that the Titan hose failure was related to the fibre reinforcement. Poor dhesion of the inner fibre reinforcing layer and differences in the mechanical properties of he fibres from the inner and outer reinforcing layers are possible causes. As only one batch f Titan hose was tested, it was not possible to determine if this is confined to this batch of ose or whether it is indicative of a more general problem resulting from the manufacturing

14. KEYWORDS, DESCRIPTORS or IDENTIFIERS (technically meaningful terms or short phrases that charactenze a document and could be helpful in cataloguing the document They should be selected so that no secunty class1f1cat1on 1s required Identifiers. such as equipment model des1gnat1on, trade name, military proiect code name. geographic location may also be included If possible keywords should be selected from a pub!Jshed thesaurus e g Thesaurus of Engmeenng and Sc1ent1f1c Terms (TEST) and that thesaurus-1dent1fled If 11 not possible to select indexing terms which are Unclass1f1ed, the class1f1calion of each should be indicated as with the title)

Refuelling Hose Failure NA TO F44 aviation turbine fuel 3-GP-24 Chemical analysis Mechanical testing Proof Pressure testing

UNCLASSIFIED

DCD03 2/06187-MI DREA mod 17 Dec 1997

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