Environment stress cracking

A.S. Maxwell, NPL Environment Stress Cracking Database, National Physical Laboratory, 1998. 

Turnbull A, Maxwell AS, Pillai S (2000) Comparative assessment of slow strain rate, 4-pt bend and constant load test methods for measuring environment stress cracking of polymers. Polym Test 19(2) 117—129... 

Maxwell AS, Turnbull A (2004) Influence of small fluctuating loads on environment stress cracking of polymers. Polym Test 23(4) 419-422... 

The molecular mass of a polymer incr ses during crosslinking and this is directly interrelated with the change of properties polymer connected with the sample deformability. The crosslinking leads to an increase of viscosity of the polymer melt, increase of the tensile strength [154], improvement of creep properties [155, 15Q, increase of the resistance against environment stress cracking [157], etc. 

This chapter presents an overview of properties and performance of polymer blends, focusing on these aspects that are outside the main domain of the other chapters in this handbook. Such properties as mechanical, chemical, and solvent effects and thermal, flame retardancy, electrical, and optical properties are discussed. Further, the developments in sound transmission, certain special test methods in aroma barrier, permeability test for hquids, and environment stress cracking are included in the second edition of this handbook. In addition, the data is updated and upgraded. And, finally, the relevant and useful websites for additional information are also provided towards the end of this chapter. 

This method is being accepted throughout Europe as the standard method to test PE pipe grade materials that exhibit very high environment stress crack resistance (ESCR) values. The FNCT test has been preferred in Europe, as it leads to shorter failure times, due to its particular specimen design and to the presence of a surface-active environment. 

A patent on reactor-blended thermoplastic olefinic elastomer, R-TPO, was disclosed. Thus, PE was polymerized in the presence of an active catalyst and an already polymerized olefinic copolymer (e.g., ethylene-co-1-butene) or the sequence was reversed. The blend had superior resistance to environment stress cracking, and the blown film showed few fish eyes... 

Screening the High-Environment Stress-Crack Resistance (ESCR) of Polyethylene... 

Environment stress cracking or F50 time p 1693] Does not stress crack... 

Resistance to Chemical Environments and Solubility. As a rule, amorphous plastics are susceptible, to various degrees, to cracking by certain chemical environments when the plastic material is placed under stress. The phenomenon is referred to as environmental stress cracking (ESC) and the resistance of the polymer to failure by this mode is known as environmental stress cracking resistance (ESCR). The tendency of a polymer to undergo ESC depends on several factors, the most important of which are appHed stress, temperature, and the concentration of the aggressive species. 

Titanium does not stress-crack in environments that cause stress-cracking in other metal alloys, eg, boiling 42% MgCl2, NaOH, sulfides, etc. Some of the aluminum-rich titanium alloys are susceptible to hot-salt stress-cracking. However, this is a laboratory observation and has not been confirmed in service. Titanium stress-cracks in methanol containing acid chlorides or sulfates, red Aiming nitric acid, nitrogen tetroxide, and trichloroethylene. 

In concert with the stress environment (stress corrosion cracking, corrosion fatigue)... 

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

In recent years several new Ni-Cr-Fe-Mo and Ni-Cr-Fe-Mo-Cu have been introduced with improved resistance to sulphide stress cracking in sour oil and gas environments. ... 

While ideally structures should be designed and fabricated so that environment-sensitive cracking is avoided, in practice it is sometimes necessary to live with the problem. This implies an ability to detect and measure the size of cracks before they reach the critical size that may result in catastrophic failure. Such inspection has important implications for plant design, which should be such as to allow inspection at relevant locations. The latter are regions of high residual stress (welded, bolted or riveted joints) and regions of geometrical discontinuity (notches, crevices, etc.) where stress or environment concentration may occur. 

In both aqueous and organic environments the crack velocity is related to the instantaneous stress intensity factor, as shown in Fig. 8.53. Three regions may be observed I, II and III. Regions I and III are not always observed and the specific relationship observed depends upon the alloy composition and heat treatment, the environmental composition and the experimental conditions. ... 

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