Table 2.

PDP restrictions and protection proficiency for X60-Steel in pickling solution (HCl) with different surfactant doses at 50 °C.

Inhibitors Code	Cinh./ mol L−1	icor/ µAcm−2 ±SD	Ecor/ mV (Ag/AgCl) ±SD	βa/ mV dec −1	−βc/ mV dec −1	θ	ZPDP/%
Blank	0.0	325.7 ± 24.2	−640	95.2	170.2	-	-
FSG6-2	5 × 10−6	164.31 ± 14.5	−651	100.8	166.8	0.495	49.55
	1.5 × 10−5	138.71 ± 10.1	−660	97.4	178.8	0.574	57.41
	3.0 × 10−5	87.09 ± 7.6	−658	98.5	181.4	0.732	73.26
	6.0 × 10−5	70.51 ± 5.9	−635	99.6	160.1	0.783	78.35
	1.0 × 10−4	46.60 ± 4.2	−648	106.4	152.3	0.856	85.69
	2.0 × 10−4	21.59 ± 2.3	−636	103.1	174.7	0.933	93.37
FSG6-4	5 × 10−6	153.86 ± 13.7	−645	99.7	180.3	0.527	52.76
	1.5 × 10−5	127.38 ± 11.3	−652	96.3	174.7	0.608	60.89
	3.0 × 10−5	67.77 ± 5.8	−638	90.7	169.1	0.791	79.19
	6.0 × 10−5	47.19 ± 4.9	−657	92.9	170.2	0.855	85.51
	1.0 × 10−4	28.75 ± 2.4	−639	98.8	180.3	0.911	91.17
	2.0 × 10−4	10.61 ± 1.5	−633	97.4	174.7	0.967	96.74
FSG6-6	5 × 10−6	141.94 ± 13.6	−642	98.5	162.4	0.564	56.42
	1.5 × 10−5	110.86 ± 9.8	−652	95.2	165.7	0.659	65.96
	3.0 × 10−5	54.97 ± 4.7	−647	96.3	170.2	0.831	83.12
	6.0 × 10−5	36.93 ± 3.1	−627	92.9	182.5	0.886	88.66
	1.0 × 10−4	17.81 ± 1.2	−630	100.8	175.8	0.945	94.53
	2.0 × 10−4	5.31 ± 1.0	−618	97.6	172.4	0.983	98.37